## Visionlearning Glossary

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AAAS   American Association for the Advancement of Science, pronounced "Triple-A ess".

Used in the following modules: Scientific Communication: The How and Why of Scientific Meetings

Absolute zero   The theoretical lowest temperature possible at which all molecular motion ceases. Absolute zero, 0 K or -273.15°C, has never been reached.

Used in the following modules: Matter: States of Matter, Temperature

Abstract   In science, an abstract is a brief statement of essential information contained within a document or presentation. An abstract is not an introduction, rather it concentrates the most pertinent information to facilitate understanding of the main points of the document. Most scientific journal articles include an abstract at the beginning of the article which is uploaded to literature databases to facilitate information searches; and scientists also submit abstracts that summarize what they will present at a scientific meeting. More information.

acceleration   The change in an object’s velocity over time, measured in distance per unit time per unit time (for example meters per second per second or m/s2). Acceleration (a) is calculated by dividing the change (symbolized by Δ, the Greek letter delta) in velocity (v) by the change in time (t):

a = Δv/ Δt.

This can also be written as:

a = v2–v1/ t2–t1, where v1 and t1 denote the starting velocity and time and v2 and t2 denote the ending velocity and time.

To illustrate, imagine a car speeding up (accelerating) from a stand still (0 meters/second) to a speed of 15 meters/seconds over the course of 5 seconds. The car’s total increase in velocity is 15 meters/second. During each of the 5 seconds that the car is accelerating, its velocity increases by 3 meters/second until it reaches its top speed. (After one second the car is traveling at a velocity of 3 meters/second; after 2 seconds, it’s traveling at a velocity of 6 meters/second, and so on). Therefore, the car’s rate of acceleration is 3 meters per second per second or 3 m/s2. Using the equation above:

a = v2–v1/ t2–t1
a = 15–0 / 5–0
a = 15/5
a = 3 m/s2

(noun)

Used in the following modules: Gravity, The Hydrologic Cycle

Accuracy   In science, the term accuracy describes how well a measurement approximates the theoretically correct value of that measurement, for example, how close an arrow strikes to the center of a target. Accuracy provides a measure of the systematic error associated with a value. Compare to precision. See the module Uncertainty.

Acid   Generally, a substance that reacts with bases to form a salt, several different definitions of acids have been proposed by different scientists (listed in parentheses). 1) (Arrhenius) a compound that releases hydrogen ions (H+) in solution; 2) (Brønsted-Lowry) a compound capable of donating hydrogen ions, 3) (Lewis) a compound that can accept a pair of electrons from a base.

Acid Rain   Rain with a pH less than 5.

Used in the following modules: The Nitrogen Cycle

Used in the following modules: Research Methods: Comparison

Activation Energy   The energy required to initiate a chemical reaction or process, abbreviated Ea. For example, a cigarette lighter requires activation energy (provided in the form of a spark) to initiate the reaction of fuel with oxygen.

Used in the following modules: Chemical Equations, Chemical Reactions

Adams, John Couch   Welsh astronomer, born near Launceston, Cornwall (1819-1892). He successfully predicted the existence of a then-unknown planet (Neptune) based on perturbations in Uranus’ orbit. He also studied the Leonid meteor shower, successfully predicting its occurrence and proving its association with Tempel’s Comet. For further information, see John Couch Adams.

Used in the following modules: Gravity

Adsorb   To adhere in an extremely thin layer of molecules (as of gases, solutes, or liquids) to the surfaces of solid bodies or liquids with which a substance is in contact.

Aesthenosphere   The semi-molten layer of the earth which starts at ~70-200 km depth and ends at 660 km depth. The aesthenosphere is part of the mantle, and is composed primarily of the rock peridotite. The aesthenosphere can flow very slowly, allowing rigid pieces of the lithosphere to move around on top of it.

Used in the following modules: Earth Structure

Agassiz, Louis   (1807-1873) A geologist and paleontologist, born and educated in Europe, but regarded as one of the founding fathers of American science. While in Switzerland and France, Agassiz studied comparative anatomy under Georges Cuvier in 1832, focusing on fossil and modern fish. In 1836, he began to study glacial landforms and became a strong proponent of the theory of glacial ice ages. In 1848, Agassiz accepted a position at Harvard University and moved to the United States, where he helped found the National Academy of Sciences, the American Association for the Advancement of Science, and served as a regent of the Smithsonian Institution. For more information, see this biography of Louis Agassiz.

Used in the following modules: Scientific Communication: The How and Why of Scientific Meetings

Age of Exploration   (15th-early 17th century) also referred to as the Age of Discovery, this was a period in history during which Europeans explored and mapped the world, establishing primary contacts with Africa, the Americas, Asia and Oceania. In particular, Portuguese and Spanish explorers made ocean voyages in search of alternative trade routes to the Indies, the source of gold, silver and spices.

Used in the following modules: Taxonomy I

Agricola, Georgius   (aka Georg Pawer/Bauer) German geologist and medical doctor, born in Glauchau, Saxony (1494-1555). Agricola wrote several influential geological manuscripts, including De Natura Fossilium (1546), De Ortu et Causis Subterraneorum (1546) and De Re Metallica (published posthumously in 1556). The later is his most influential work, being a compendium of everything then known about mining, including (but not limited to) equipment, methods of surveying for and extracting minerals, mine administration, and the occupational diseases of miners. For further information, see
Georgius Agricola.

Used in the following modules: Minerals I

Used in the following modules: Scientific Communication: The How and Why of Scientific Meetings, Scientific Institutions and Societies

Alchemy   A medieval chemical philosophy concerned principally with the transformation of base metals into gold, and the discovery of an elixir of life.

Alcohol   An organic compound containing a hydroxyl group. Common examples include methanol (CH3OH) and ethanol (CH3CH2OH).

Used in the following modules: Organic Chemistry, Temperature

Alexander the Great   Alexander III (356–323 BC) was a Greek king of Macedon. He created one of the largest empires in ancient history and was reputed to be undefeated in battle. He is still considered one of the most successful military commanders in history, and is remembered for his tactical ability. His conquests spread Greek culture into the East; certain aspects of the resulting Hellenistic culture lasted in the Byzantine Empire until the mid 15th century.

Alhazen   The Latinized name for the Muslim scientist Abū ‘Alī al-Hasan ibn al-Hasan ibn al-Haytham who was born in Basra, Mesopotamia (Iraq) (965-1039 CE). Alhazen made significant contributions in the fields of astronomy, mathematics, medicine, and most significantly, optics. His work in optics irrefutably proved that vision is a function of external light rays entering the human eye; and his rigorous and quantitative approach formed the basis of the modern experimental method in science. For further information see Alhazen

Alkanes   A group of hydrocarbons with the general formula CnH(2n+2). Alkanes contain no carbon-carbon multiple bonds; common examples include methane and propane.

Used in the following modules: Organic Chemistry

Alkenes   A group of hydrocarbons with the general formula CnH(2n). Alkenes contain at least one carbon-carbon double bond; common examples include ethylene.

Used in the following modules: Organic Chemistry

Alkyne   A group of hydrocarbons with the general formula CnH(2n-2). Alkynes contain at least one carbon-carbon triple bond; common examples include ethyne also known as acetylene.

Used in the following modules: Organic Chemistry

allele   A variation of a genetic element, usually resulting in a distinct trait.

(noun)

Used in the following modules: Genetics I, Ideas in Science: Theories, Hypotheses, and Laws

Alpha particle   A type of particle that is ejected from radioactive nuclei. Alpha particles consist of two protons and two neutrons and thus are equivalent to helium nuclei.

Used in the following modules: Atomic Theory I, Nuclear Chemistry

Alternative hypothesis   In statistical testing, an alternative hypothesis (H1) is a statement describing the possibility that an observed result or effect is genuine. The alternative hypothesis is always compared to a null hypothesis (H0), and H1 is not accepted until statistical testing shows that it should be accepted in favor of H0. For example, in an evaluation of data regarding the pain relieving properties of a new drug, the alternative hypothesis would state that the new drug has an effect on pain relief compared to a control. Accepting H1 does not indicate that the observed result or effect is large or important, simply that it is favored in terms of probability of the outcome.

Used in the following modules: The Case of the Ivory-billed Woodpecker

Alveolar   Pertaining to an alveolus.

Used in the following modules: Absorption, Distribution and Storage of Chemicals

Alveolus   A small sac-like structure in the body, especially common in the lung. A lung alveolus has extremely thin walls that aid in the exchange of gases including O2 and CO2.

American Association for the Advancement of Science   A professional society established in 1848 that serves scientists in all disciplines. The mission of AAAS is to "advance science, engineering, and innovation throughout the world for the benefit of all people." AAAS hosts an annual meeting, publishes the journal Science, and has numerous programs that promote science education and the interactions between science and policy. More information about AAAS can be found on their website.

American Chemical Society   A professional society for chemists established in 1876. The mission of ACS is “to advance the broader chemistry enterprise and its practitioners for the benefit of Earth and its people.” In addition to publishing journals and holding meetings, ACS provides competitive funding for research through its Petroleum Research Fund. More information about ACS can be found on their website.

Used in the following modules: Scientific Communication: The How and Why of Scientific Meetings, Scientific Ethics, Scientific Institutions and Societies

American Geophysical Union   A professional society established in 1919, originally as part of the National Academy of Sciences, but now an independent organization. The mission of AGU is “to promote discovery in Earth and space science for the benefit of humanity”; the primary means of achieving that mission is through hosting two annual meetings and publishing numerous journals. More information about AGU can be found on their website.

Used in the following modules: Scientific Communication: The How and Why of Scientific Meetings, Scientific Institutions and Societies

Amino Acid   Biochemical molecules that contain at least one amine group (-NH2) and at least one carboxylic acid group (-COOH) and conform to the general formula NH2-R-COOH, where R is an organic molecule. Amino acids are essential basic building blocks of proteins.

Used in the following modules: DNA I, Fats and Proteins

Ampére, Andre   French mathematician born in Poleymieux, Lyon (1775-1836). Ampére researched metaphysics, physics, and chemistry, but he focused on mathematics, which he taught at the Ecole Polytechnique in Paris. His key contributions to science include his work on partial differential equations, the discovery of fluorine, and studies on the wave theory of light. His most important work was the Memoir on the Mathematical Theory of Electrodynamic Phenomena, Uniquely Deduced from Experience, in which he described a mathematical derivation for the electrodynamic force law. The Amp (a measurement of electrical current) is named in his honor. For further information see Andre Ampére.

Amphibious   Having the ability to live both on land and in water.

Used in the following modules: Adaptation

andean margin   A convergent plate boundary, where oceanic crust is being subducted beneath continental crust. Named after the Andes Mountains in South America, which are the classic example of a continent-ocean convergence.

Used in the following modules: Plate Tectonics II

Andesite   An extrusive igneous rock of intermediate composition, often gray in color. The main minerals present in andesite are plagioclase and hornblende. The word “andesite” comes from the Andes Mountains in South America, where this rock type is common. Around the world, andesitic magma erupts out of volcanoes along convergent boundaries, and its intrusive equivalent is diorite.

Used in the following modules: Minerals III, The Rock Cycle

Ångstrom   A unit of length equivalent to 10-10 meters. 1Å = 0.0000000001 m.

Anion   An ion that migrates to the anode in an electrical cell; a negatively charged ion.

Used in the following modules: Minerals II, Minerals III

Anode   A positively charged terminal in an electrical cell.

Anomaly   A deviation from the normal or expected, sometimes expressed with respect to an average value. Anomalies are described in many kinds of data, and are features of datasets that require explanation.

Anther   Male part of a flowering plant that holds pollen.

Used in the following modules: Genetics I, Scientists and the Scientific Community

Antibody   a protein that is produced by the immune system in response to infection by an antigen. Different antigens provoke the production of different antibodies. Antibodies attach themselves to antigens, destroying them or surrounding them so that they cannot attack the body.

Antigen   a substance that stimulates the production of an antibody by the immune system. Antigens include toxins, bacteria, foreign blood cells, and cells of transplanted organs.

Used in the following modules: Cells

apex predator   (Also known as top-level predator or alpha predator) A carnivorous species at the top of the food chain in a particular ecosystem with no natural predators other than humans. Examples include large cats (lions, jaguars, tigers, etc.), sharks, wolves, bears, anaconda snakes, and others. Removing these top predators can have ripple effects throughout an ecosystem.

(noun)

Used in the following modules: Tracking Endangered Jaguars with Sergio Avila

aquatic   Related to, located in, or living in or on a body of water. Not terrestrial. Aquatic includes both freshwater and saltwater (marine) environments.

Used in the following modules: The Nitrogen Cycle

Aquifer   A porous and permeable body of rock or sediment through which groundwater flows.

Used in the following modules: The Hydrologic Cycle

Archimedes   Greek mathematician, born in Syracuse, Sicily (287-212 BCE). Little is known about Archimedes’ life, but he is best known for devising the water displacement method of measuring the volume of an irregularly-shaped object (which he possibly conceived of while getting into his bathtub). He is also credited with developing the foundations of integral calculus and mathematical physics. For further information see Archimedes.

Used in the following modules: Density

Aristotle   A Greek philosopher born in Stagira (384-322 BCE). He joined Plato’s Academy in Athens (then being run by Eudoxus) at the age of 17. After attending the academy, he taught there for 20 years before founding his own school, the Lyceum. He is remembered primarily for his works on deductive logic and the use of philosophical reasoning to address questions about the natural world. For further information see Aristotle.

Used in the following modules: Charles Darwin I, Charles Darwin III, Light I, Matter, Research Methods: The Practice of Science, Taxonomy I, The Nature of Scientific Knowledge

Arrhenius, Svante   Swedish physical chemist born in Vik (1859-1927). Arrhenius is most famous for what is now known as the Arrhenius equation, which relates the rate of chemical reactions to temperature and activation energy. Arrhenius was awarded the Royal Society’s Davy medal and the Faraday medal of the Chemical Society in 1914, and the Nobel Prize for Chemistry in 1903 based on his early work on the conductivity of electrolytes in solution. For further information see Svante Arrhenius.

Used in the following modules: Acids and Bases

artery   a blood vessel that conveys oxygenated blood away from the heart to other parts of the body.

Used in the following modules: Research Methods: Comparison

Atom   The smallest unit of an element that retains the chemical properties of the element. Atoms can exist alone or in combinations with other atoms forming molecules.

Atomic mass   The average mass of an atom of an element, usually expressed in atomic mass units. The term is often used interchangeably with atomic weight.

Used in the following modules: Atomic Theory I, Atomic Theory II, Classic Experiment: Meselson and Stahl, Density, Nuclear Chemistry

Atomic mass unit   One atomic mass unit (amu or u) is defined as 1/12 the mass of the standard carbon-12 isotope, or 1.66 × 10-27 kg.

Atomic number   The number of protons in an atomic nucleus.

Used in the following modules: Atomic Theory II, Nuclear Chemistry, The Periodic Table of Elements

atomic unit   Compare with Bohr radius and hartree. A system of non-SI units used in quantum chemistry to simplify calculations and mathematical expressions. The definitions of atomic units include physical constants (like the speed of light, the rest mass of the electron, and other quantities that never change), so that all constants drop out of expressions when atomic units are used.

atomic weight   As listed on the periodic table, the atomic weight is a weighted average of the masses of stable isotopes of an element that occur in nature. Given in grams, the atomic weight is the weight of one mole of atoms of an element. Atomic weight is often used interchangeably with atomic mass.

Used in the following modules: Matter, Nuclear Chemistry, The Mole, The Periodic Table of Elements

Attenuation   The behavior of waves as they radiate out from a source. As distance from the source increases, intensity of the waves decreases. Attenuation occurs because the same amount of energy is being spread out over a larger area.

Used in the following modules: Earth Structure

Avery, Oswald   (October 21, 1877 – 2 February 1955) A Canadian-born American physician and medical researcher, considered one of the founders of immunochemistry, a branch of chemistry that deals with the immune system. Avery was part of the team, along with Maclyn McCarty and Colin MacLeod, which discovered that DNA is the genetic basis of life. Later, Avery served as president of the American Association of Immunologists, the American Association of Pathologists and Bacteriologists, and the Society of American Bacteriologists, and received numerous honors and recognitions for his medical research.

Used in the following modules: DNA I

Used in the following modules: The Mole

Bacon, Francis   English statesman and philosopher born in London (1561-1626). In 1620, Bacon published the Novum Organum, in which he argued for a method of scientific inquiry based on inductive reasoning in which the only way to discover the truth was to gather evidence from the real world. He is often referred to as the catalyst for the Scientific Revolution. In 1618, Bacon was appointed Lord Chancellor, and in 1621, he was made viscount St. Albans. For further information see Francis Bacon

Used in the following modules: Research Methods: The Practice of Science, Scientific Institutions and Societies

Bacteriophage   any of a group of viruses that infect and reproduce in specific bacteria, usually causing their disintegration or dissolution. After the bacterium is destroyed, the bacteriophage is released and can invade surrounding bacteria.

Used in the following modules: DNA I

Basalt   A dark, fine-grained igneous rock formed by cooling of iron- and magnesium-rich lava above the surface of the earth. Basalt is the main component of the oceanic crust of the earth.

Used in the following modules: Earth Structure, Minerals I, The Rock Cycle

Base   Generally, a substance that reacts with acids to form a salt, several different definitions of bases have been proposed by different scientists (listed in parentheses). 1) (Arrhenius) a compound that releases hydroxide ions (OH-) in solution; 2) (Brønsted-Lowry) a molecule or ion that accepts hydrogen ions from solution; 3) (Lewis) a molecule or ion that donates an electron pair to an acid.

Used in the following modules: Acids and Bases, Creativity in Science, DNA I, DNA II, Earth Structure, Scientific Communication: Utilizing the Scientific Literature

Bateson, William   (August 8, 1861 – February 8, 1926) A British geneticist who was the first person to use the term genetics to describe the study of biological inheritance and heredity. In addition, he was largely responsible for popularizing the ideas of Gregor Mendel following their rediscovery in 1900 by Hugo de Vries, Erich Tschermak von Seysenegg and Carl Correns. Bateson’s most famous work, Materials for the study of variation, was published in 1894. In it, he cataloged physical variations in animal specimens, such as bees with legs instead of antenna, and humans with polydactylism (extra fingers) or extra ribs.

BCE   An abbreviation for Before the Common Era, which is a designation for the period of time prior to year 1 of the Gregorian calendar. BCE is an alternative to the abbreviation BC, and the numbering of years is identical to the Before Christ system. Compare with CE.

Becquerel, Henri   French physicist, born in Paris (1852-1908). Becquerel’s most famous work is his study of uranium salts, which he discovered produced rays that caused gas to ionize. This type of radiation was termed Becquerel radiation. In 1903 he was awarded half a Nobel Prize for his discovery of radiation; the other half was awarded to Pierre and Marie Curie for their work on Becquerel radiation. For further information see Henri Becquerel.

Used in the following modules: Nuclear Chemistry

Bernoulli, Daniel   Swiss medical doctor and mathematician born in Groningen (1700-1782). His work Hydrodynamica contains the first correct analysis of the dynamics of water flowing through a hole, based on the principle of the conservation of energy. He was a prolific researcher and won the Grand Prize of the Paris Academy 4 times, for topics in astronomy and nautical topics. For further information see Daniel Bernoulli.

Used in the following modules: Matter

Berzelius, Jöns Jakob   Swedish chemist and medical doctor born in Väversunda, Ostergötland (1779-1848). While studying for his medical degree, Berzelius experimented with the use of electric shock to treat patients with various diseases. He is most famous for a series of experiments that proved that elements in inorganic compounds are bound together in definite proportions. In studying compounds, he discovered cerium, selenium, and thorium. With his experimental results, he was able to determine the atomic weights of nearly all elements then known. For more information, see Jöns Jakob Berzelius.

Used in the following modules: Minerals III

Big Bang   A theory proposed by Georges Lemaitre (originally known as the “hypothesis of the primeval atom”) describing the origin of the universe. It was based on the idea that if the space between galaxy clusters is continuing to increase, then there had to be a time when these same bodies were closer together. The term “Big Bang” was coined by Fred Hoyle in 1949 to describe an event 13.7 million years ago involving the rapid expansion of matter and energy from a single hot, dense point. This expansion and cooling provided a foundation for the creation of the Universe.

Used in the following modules: Plate Tectonics I

binary stars   a term coined by Sir William Herschel in 1802 to describe a pair of stars that revolve around a common mass and are unaffected by the mass of other stars, creating their own system.

(noun)

Used in the following modules: The Nature of Scientific Knowledge

binomial   A formal two word name given to each species, based on the combination of a genus name and a species name.

Used in the following modules: Taxonomy II: Nomenclature

biodiversity   The variety and abundance of life and its ecological context, including the different kinds of organisms, the numbers of species, the variations in their genes, and the complexity of their ecological conditions.

Used in the following modules: Charles Darwin III, Taxonomy I, Taxonomy II: Nomenclature, Tracking Endangered Jaguars with Sergio Avila

Biogeochemical   of or relating to the partitioning and cycling of chemical elements and compounds between the living and nonliving parts of an ecosystem

Used in the following modules: Earth's Atmosphere, Studying Climate Change with Kevin Arrigo, The Carbon Cycle, The Nitrogen Cycle

Biomass   The combined mass of living or once-living organisms in a given area.

Used in the following modules: The Nitrogen Cycle

biome   A large, distinct biological community characterized by vegetation and wildlife adapted to particular environmental conditions, such as climate and soil type. Examples include desert, grassland, and tundra.

(noun)

Used in the following modules: Tracking Endangered Jaguars with Sergio Avila

bioregion   (Also known as ecoregion) A large area of land or water defined by its natural features, rather than political boundaries like state lines or international borders. A bioregion is an area with similar ecosystems and natural resources, sharing features like soil types, currents, climate, geological features, vegetation, and wildlife.

For example, the Commission for Environmental Cooperation of North America lists 181 terrestrial ecoregions and 86 marine ecoregions. These include areas like the Ozark Highlands and the Sonoran Desert on land and the Puget Sound Estuarine Area and Central Hudson Bay in the water. Classification systems vary, and not all scientists agree on the exact number or boundaries of Earth’s bioregions. But the concept is useful for managing wildlife and natural resources on a large scale.

(noun)

Used in the following modules: Tracking Endangered Jaguars with Sergio Avila

Biosphere   All of the living organisms on Earth.

Bjerknes, Vilhelm   Norwegian mathematician, physicist and meteorologist born in Christiana, Norway (now Oslo) (1862-1951). Bjerknes proposed the concept of numerical weather prediction, developed by later scientists as a means of weather forecasting through the use of mathematical modeling. Bjerknes also made fundamental contributions to our understanding of air masses, fronts, and circulation in the atmosphere. He received many honors during his life, and posthumously was honored by a stamp with his image. For further information see Vilhelm Bjerknes

Used in the following modules: Ideas in Science: Scientific Controversy, Research Methods: Modeling

Blueprint   a detailed outline or plan of action. The word technically refers to a process of photographic printing, used chiefly in copying architectural and mechanical drawings, which produces a white line on a blue background.

Used in the following modules: Charles Darwin III, DNA I, DNA II, Tracking Endangered Jaguars with Sergio Avila

Blueshift   Occurs when the observed light from an object appears to be of a shorter wavelength (bluer) than what is actually emitted. Blueshift is caused by the Doppler Effect, when a source of light moves toward an observer. See also redshift.

Bohr, Niels   Danish physicist born in Copenhagen (1885-1962). Bohr’s research was mainly theoretical in nature, including an investigation into the absorption of alpha rays and the structure of atoms. He combined Rutherford’s atomic model with concepts from the Quantum Theory, developing the model of the atom that is still used today. He was awarded the Nobel Prize in Physics in 1922 for his work on atomic structure. For further information, see Niels Bohr.

Used in the following modules: Atomic Theory II

Bose, Satyendra Nath   Indian Bengali mathematician born in Calcutta (1894-1974). Bose developed an interest in physics and mathematics in high school. He later worked on quantum theory, particularly Planck’s law of black body radiation. His 1924 paper Planck’s Law and the Hypothesis of Light Quanta was strongly endorsed by Einstein, and helped to form the foundation for Bose-Einstein statistics and the theory of Bose-Einstein condensates. The boson, a sub-atomic particle with integer spin, is named in his honor. For more information see Satyendra Nath Bose.

Used in the following modules: Matter: States of Matter

Boyle, Robert   English chemist and theologian, born at Lismore Castle, Munster, Ireland (1627-1691). Boyle published on a broad array of topics, including chemistry, physics, medicine, and theology. He is best known for Boyle’s Law, from which the ideal gas law is derived. In 1661, Boyle published The Sceptical Schymist or Chymico-Physical Doubts and paradoxes, which is considered a conerstone in the field of modern chemistry. Boyle was also one of the founding members of the Royal Society of London. For further information see Robert Boyle

Used in the following modules: Acids and Bases, Matter, Scientific Institutions and Societies, Waves and Wave Motion

Brahe, Tycho   Danish astronomer, born in Knutstorp Castle (1546-1601). He is famous for his geocentric theory of the solar system, as well as for his meticulous astronomical observations concerning the positions of planets. He made his observations over 20 years, from the island of Hven. He later was appointed Imperial Mathematician to the Holy Roman Emperor, Rudolph II, in Prague. For further information see Tycho Brahe.

Used in the following modules: Gravity

breeding population   A group of animals of a particular species that is large enough and close enough together to successfully produce offspring. Larger breeding populations tend to have higher genetic diversity, which can help a species withstand natural or human-driven changes in the environment. Species that have large geographic ranges may have multiple breeding populations in different locations that do not interbreed with one another. A small breeding population may also be assembled in captivity, such as at a zoo, in order to help boost the population of a species that is threatened in the wild.

(noun)

Used in the following modules: Tracking Endangered Jaguars with Sergio Avila

Brønsted, Johannes   Danish physical chemist born in Varde (1879-1947). In 1906, Brønsted published his first paper on electron affinity. In 1923, he suggested the protonic theory of acid-base reactions, and later became an authority on catalysis by acids and bases. The Brønsted catalysis equation is named for him. He also developed the theory of proton donors during ionization. For further information see Johannes Brønsted.

Used in the following modules: Acids and Bases

Buffer   A substance that when added to solution compensates for any change in hydrogen ion concentration following the addition of an acid or a base, and thus maintains a relatively constant pH. Buffers can react with and neutralize small amounts of either acids or bases.

buoyant force   The upward pressure exerted on an object by a fluid in which the object rests.

Used in the following modules: Density

Bush, Vannevar   American scientist and statesman, born in Everett, Massachusetts (1890-1974). Bush did seminal work in analog computing, and founded the American Appliance Company, later renamed Raytheon. In 1939 he was appointed chairman of the National Advisory Committee for Aeronautics and began advocating for the establishment of a federal agency to coordinate scientific research, especially as related to military and defense needs. The effort would eventually lead to the creation of the National Science Foundation in 1950. For further information see: Vannevar Bush.

Used in the following modules: Scientific Communication: Utilizing the Scientific Literature, Scientific Institutions and Societies

Calcareous   Containing calcium.

Calibrate   To determine or check the accuracy of an instrument used for quantitative measurements, or to make corrections in or to adjust an aspect of a system.

Carbonic Acid   The weak acid formed when CO2 dissolves in water.

Used in the following modules: Acids and Bases, The Carbon Cycle

Carnot Cycle   A theoretical formulation of the most efficient thermodynamic cycle capable of converting thermal energy into work, and work into thermal energy. A defining characteristic of the Carnot cycle is that it does not consider a change in entropy, and thus cannot exist in real practice. Like the Third Law of Thermodynamics, the Carnot Cycle serves as a reference point in measuring efficiency and entropy in heat engines.

Used in the following modules: The Nature of Scientific Knowledge

Carnot, Sadi   Physicist and military engineer, born in Paris, France (1796-1832). Carnot authored Reflections on the Motive Power of Fire in 1824, which provided the first account of the theoretical workings of heat engines. Carnot’s descriptions of energy transfer within heat engines provided the foundation for the Second Law of Thermodynamics. See Carnot Cycle.

Used in the following modules: The Nature of Scientific Knowledge

Carpel   (also called Pistil) Female part of a flowering plant consisting of ovary with ovules and stigma/stamen structures to receive pollen.

Used in the following modules: Genetics I

Cartesian Plane   The Cartesian plane, named after the mathematician Rene Descartes, is a plane with a rectangular coordinate system that associates each point in the plane with a unique pair of numbers in an ordered pair of the form (x,y). The x value is the horizontal coordinate and the y value is the vertical coordinate.

Used in the following modules: Wave Mathematics

Cathode   A negatively charged terminal in an electrical cell.

Used in the following modules: Atomic Theory I, The Process of Science

Cathode ray   A negatively charged beam of particles (electrons) that are emitted from the negative terminal in a vacuum tube.

Used in the following modules: The Process of Science

Cation   An ion that migrates to the cathode in an electrical cell; a positively charged ion.

Used in the following modules: Minerals III

Cavendish, Henry   English chemist and physicist born in Nice, France (1731-1810). Cavendish’s most important work was isolating hydrogen and describing its properties. He also researched electrical capacitance and used a torsion balance (now named for him) to measure the gravitational constant (G), which allowed him to calculate the mass of the Earth. For further information, see Henry Cavendish.

Used in the following modules: Gravity

CE   An abbreviation for Common Era, which is a designation for the period of time beginning with year 1 of the Gregorian calendar. CE is an alternative to the abbreviation AD, and the numbering of years is identical to the Anno Domini system. Compare with BCE.

Celsius, Anders   Swedish astronomer born in Uppsala (1701-1744). In 1742, Celsius invented the centigrade temperature scale, using the freezing and boiling points of water as his reference temperatures. Interestingly, he defined the freezing point as 100° and the boiling point as 0°. The scale was reversed to its present form after his death. Celsius also was the first to suggest that the aurora has a magnetic cause. For further information see Temperature

CFC   chlorofluorocarbon

Used in the following modules: Research Methods: The Practice of Science

Chadwick, James   English physicist born in Bollington, Cheshire (1891-1974). Chadwick worked with Ernest Rutherford on the disintegration of atoms by bombarding them with alpha particles. He was awarded the Nobel Prize in physics in 1935 for his discovery of the neutron. For further information, see James Chadwick.

Used in the following modules: Atomic Theory I

Chambers, Robert   (10 July 1802 – 17 March 1871) was a Scottish author, journal editor and publisher who was highly influential in mid-19th century scientific circles. His most famous book is Vestiges of the Natural History of Creation, published anonymously in 1844, in which he argues for transmutation, an evolutionary view of life similar to that proposed by Jean-Baptiste Lamarck, an unpopular view with both the scientific community and society in general. Charles Darwin credited Chambers with preparing people to accept the theory of evolution by natural selection.

Used in the following modules: Charles Darwin III

Chapman, Sydney   British-American geophysicist and mathematician born in Eccles, Lancashire (1888-1970). In 1939, Chapman co-authored the classic work The Mathematical Theory of Non-Uniform Gases. The following year, he co-authored the two-volume work Geomagnetism. His most famous work in mathematics was his research in stochastic processes, for which he developed (independently of Andrey Kolmogorov) the Chapman-Kolmogorov equations. For further information see Sydney Chapman.

Used in the following modules: Earth's Atmosphere

Chargaff, Erwin   (also known as Edwin Chargaff) Austrian-Jewish biochemist born in Czernowitz, Ukraine (then part of Austria-Hungary) in 1905. Chargaff immigrated to the United States in 1935 and died in New York City in 2002. He is best known for discovering two rules about DNA chemistry that significantly advanced the field of molecular biology. Chargaff’s First Rule is that the number of adenine base units in DNA is equal to that of thymine, and the number of cytosine base units is equal to that of guanine (A = T, C = G). This was an important clue for James Watson and Frances Crick as they worked on solving the molecular structure of DNA. The Second Rule is that the composition of DNA, in terms of the relative amount of A, T, G, and C bases, varies from species to species. This was significant evidence for Oswald Avery’s hypothesis that DNA carries hereditary information. For a more comprehensive biography, see Erwin Chargaff.

Used in the following modules: Creativity in Science, DNA II

Chase, Martha   (1927 – August 8, 2003), also known as Martha C. Epstein, an American geneticist and member of the team whose experiments showed that DNA, and not protein, comprises genetic material. Chase received her PhD from the University of Southern California in 1964, but her scientific career ended shortly thereafter due to illness, and she suffered from debilitating short-term memory loss until her death in 2003.

Used in the following modules: DNA I

Chemical bond   A link between atoms. See ionic bond and covalent bond.

Used in the following modules: Chemical Bonding, Chemical Equations, Chemical Reactions

Chemical reaction   A process in which atoms and molecules recombine by forming or breaking chemical bonds. Chemical reactions form new products that have different chemical properties than the initial reacting material.

Chlorofluorocarbons   Compounds consisting of carbon, chlorine, fluorine, and sometimes hydrogen once used widely as aerosol propellants and refrigerants. The realization that chlorofluorocarbons cause depletion of the stratospheric ozone layer led to a sharp decrease in their use mandated by the Montreal Protocol in 1989.

Used in the following modules: Research Methods: The Practice of Science

Chromosome   The organized genetic structure of DNA with associated proteins that contains the hereditary information necessary for reproduction, protein manufacture, and other functions.

Used in the following modules: Creativity in Science, DNA I, From Stable Chromosomes to Jumping Genes, Genetics I

circulatory system   the system of organs and tissues that circulates blood through an organism, including the heart, blood, arteries, and veins.

Used in the following modules: Adaptation

citizen scientist   A person (usually a volunteer or student) who is not a professional scientist but contributes to scientific research. Some citizen scientists assist researchers in analyzing large data sets. Others help by reporting things like rainfall or bird species observed in their backyards. Successful projects, such as those run by the Cornell Lab of Ornithology and the National Weather Service, often rely on volunteers in many locations making repeated observations over time. This can allow citizen science projects to achieve results that a single scientist or small team of researchers could not.

See how citizen scientists have contributed to scientific knowledge through projects at the Cornell Lab of Ornithology and the National Weather Service. Visit the National Science Foundation to learn more about citizen science or explore Scientific American’s list of citizen science projects that need volunteers.

(noun)

Used in the following modules: Tracking Endangered Jaguars with Sergio Avila

classification   In biology, the arranging of groups of organisms into sets or divisions on the basis of their evolutionary relationships.

Used in the following modules: Authoring Modules II, Ideas in Science: Theories, Hypotheses, and Laws, Minerals II, Plate Tectonics II, Taxonomy I

Clausius, Rudolf   (aka Rudolph Gottlieb) Physicist and mathematician, born in Koszalin, Poland (1822-1888). Clausius authored On the Moving Force of Heat and the Laws of Heat which may be Deduced Therefrom in 1850. This text explored the mechanical theory of heat and the contradictions between the Carnot Cycle and the conservation of energy. In 1865, Clausius provided the first description of, and mathematical formula for entropy.

Used in the following modules: The Nature of Scientific Knowledge

Combustion   Commonly referred to as burning, a chemical reaction between a fuel (for example wood) and an oxidizing agent (for example oxygen) that produces heat (and usually, light).

Used in the following modules: Organic Chemistry

Compound   A material formed by the chemical combination of elements in defined proportions. Compounds can be chemically decomposed into simpler substances.

Conchoidal fracture   A type of breakage that produces a smooth, curved surface. Conchoidal fracture occurs when a substance has uniform strength in all directions and no pre-existing planes of atomic weakness. This generally occurs in two types of substances: minerals like quartz whose atomic structure consists of equally strong bonds in all directions, and volcanic glass, called obsidian, which has no definitive crystal structure.

Confirmation Bias   The tendency to search for or interpret new information in a way that confirms one's preconceptions and avoid information and interpretations that contradict prior beliefs.

Conic Section   A curve formed by the intersection of a cone with a plane. This often results in a circle, ellipse or parabola. For more on conic sections, visit Mathworld's Conic Sections lesson.

Used in the following modules: Gravity

conservation   Careful use of natural resources to minimize waste or damage to the natural world and to maintain natural resources for long-term human use. Historically, conservation has been contrasted with preservation—a strategy of setting aside resources and wild areas for protection from human impacts. In common usage, though, conservation has come to mean any activity that protects or restores the natural environment.

(noun)

Used in the following modules: Energy, Research Methods: Modeling, The Hydrologic Cycle, Tracking Endangered Jaguars with Sergio Avila

conservation biology   An interdisciplinary branch of science focused on understanding and maintaining Earth's biodiversity and the natural processes that create and sustain it. Conservation biologists study the impacts that humans have on biological diversity (variety) from the genetic level to the whole ecosystem level. They also develop practical ways to protect and restore that diversity.

While it has roots in the older field of ecology, conservation biology is a young scientific discipline. It emerged as its own recognized field of study in the 1980s, though wildlife managers in Australia and Europe had been using the term and practicing some of its tenets (principles) for several decades.

Biologist and founder of the Society for Conservation Biology Michael Soulé wrote one of the first formal explanations of the field in his 1985 paper "What is conservation biology?" Soulé and other early supporters called it a "crisis discipline" because it arose in response to concern over extinction and global loss of biodiversity.

At its core, conservation biology is an applied science with certain goals and values built into it. Like all scientists, conservation biologists seek knowledge about the natural world. But they also suggest ways to apply that knowledge to a real-world problem: biodiversity loss.

Modern conservation biologists draw on wide-ranging disciplines like genetics, physiology, forestry, social science, and many others. They employ a number of tools and approaches in their efforts to study and protect biodiversity. Some of the most common are nature reserves designed to protect species and their habitats and captive breeding programs to help boost wild populations.

Conservation biologists fill many roles, including academic researchers, government wildlife managers and land use planners, breeders at zoos and aquaria, and scientists and advocates working for non-profit groups.

To learn more about the profession and its history, download Soulé's classic paper "What is conservation biology?" and visit the Society for Conservation Biology. To learn about global efforts to conserve biodiversity, explore the United Nations Convention on Biological Diversity.

(noun)

Used in the following modules: Tracking Endangered Jaguars with Sergio Avila

Continental crust   The uppermost layer of the earth that forms the continents. Unlike oceanic crust, continental crust is created and destroyed very slowly, so there is some continental crust on the earth as old as 4 billion years. Continental crust ranges from 10-70 km thick and is composed primarily of granite.

Used in the following modules: Earth Structure, Plate Tectonics II

continental drift   The theory proposed in 1915 by Alfred Wegener, a German geophysicist and meteorologist. The theory stated that the continents had once been joined into one “supercontinent,” called Pangaea. About 200 million years ago, Pangaea broke apart and the continents drifted to their present positions. Wegener based his theory on the similarity of fossils and rock types on the east coast of South America and the west coast of Africa. The theory was widely ridiculed at the time because Wegener had not proposed a driving force for such drift.

Used in the following modules: Plate Tectonics I, Plate Tectonics II

Control   In science, a control is a system for which the expected change or outcome is well known and is measured or observed for the purpose of comparing it to a treatment group in scientific research. The control is used as a standard to compare or quantify change in the treatment. For more information, see: Research Methods: Experimentation

convection   The movement or circulation of a fluid due to variations in its density as a result of the transfer of heat within the fluid.

Used in the following modules: Earth Structure, Plate Tectonics II, The Rock Cycle

convergent boundary   A plate boundary where two plates are moving towards each other.

Cope, Edward Drinker   American paleontologist, born near Philadelphia, Pennsylvania (1840-1897). Cope was a prolific writer and very successful fossil-hunter, publishing over 1200 papers during his career. He developed Cope’s law, stating that mammalian species become larger over time. Cope was especially interested in the natural history of reptiles and amphibians, publishing Bactrachian of North America and The Crocodilians and Snails of North America. Copeia, the leading scientific journal in the field of herpetology is named in his honor. For further information see Edward Drinker Cope.

Used in the following modules: Taxonomy II: Nomenclature

Copernicus, Nicolaus   (Mikolaj Kopernik or Nicolaus Koppernigk) Polish astronomer born in Torun in the Royal Prussia region of the Kingdom of Poland (now Poland) (1473-1543). Copernicus was the first European scientist to provide scientific evidence for a heliocentric view of the solar system. In 1543, Copernicus published De revolutionibus orbium coelestium, often considered the origin of the Scientific Revolution. For further information see Nicolaus Copernicus

Used in the following modules: Gravity, Research Methods: The Practice of Science

Core   The innermost layer of the earth, which starts at ~2900 km depth. The core is composed mainly of iron and consists of a molten outer core and a solid inner core.

Correlation   Correlation, as measured by the correlation coefficient, provides a measure of the strength and direction of a linear relationship between two random variables. While there are many measures of correlation, among the best known is the Pearson product-moment correlation, which ranges from -1 to 1. A correlation coefficient close to -1 indicates a strong negative correlation; a correlation coefficient close to 0 indicates little correlation; and a correlation coefficient close to 1 indicates a strong positive correlation.

Used in the following modules: Data: Statistics, Research Methods: The Practice of Science, Scientists and the Scientific Community, The Hydrologic Cycle

Correns, Carl   (September 10, 1864 - February 14, 1933) German botanist and geneticist. He is remembered for his independent discovery of the principles of heredity and for his rediscovery of Gregor Mendel's earlier work on that subject. Correns also discovered cytoplasmic inheritance, that is, the influence of extra-chromosomal factors on phenotype. Unfortunately, most of Correns’ work was unpublished and was destroyed when the Allies bombed Berlin in 1945.

Used in the following modules: Genetics II

Cortes, Hernando   (1485 – December 2, 1547) was a Spanish conquistador. In the early 16th century, he led the expedition that caused the fall of the Aztec Empire, bringing much of mainland Mexico under the rule of the King of Castile. Cortes used the very effective strategy of making allies with some of the native tribes, and using these allies to attack other native tribes. The King of Castile awarded Cortes the title of Marqués del Valle de Oaxaca for his success in overthrowing the Aztec Empire.

Cosmic Microwave Background Radiation   (CMBR) a faint thermal radiation that exists in all of space. Theorized to be residual energy resulting from the Big Bang, this energy fills the Universe almost uniformly.

Used in the following modules: The Nature of Scientific Knowledge

Coulomb   A metric unit of electrical charge equal to the charge on 6.24 × 1018 electrons.

Covalent Bond   A very strong chemical bond formed by the sharing of a pair of electrons. Multiple covalent bonds can be formed when multiple pairs of electrons are shared between atoms. Covalent bonds are generally characterized in two types, polar and non-polar covalent bonds. Compare to ionic bond, hydrogen bond.

Used in the following modules: Chemical Bonding

Covalent molecule   A molecule held together by covalent bonds, that is, pairs of electrons shared between atoms. Covalent molecules are true chemical molecules whose interaction with other molecules is influenced by whether a polar molecule or non-polar molecule is formed.

Used in the following modules: Chemical Bonding, Water

Crick, Francis   English molecular biologist, physicist, and neuroscientist, most noted for being one of the co-discoverers of the structure of the DNA molecule in 1953. He later contributed to the successful deciphering of the genetic code of DNA. For further information see Francis Crick

Used in the following modules: Creativity in Science, DNA II, DNA III

critical habitat   In the context of the U.S. Endangered Species Act, the geographic area that is essential to conserving a threatened or endangered species. The U.S. Fish and Wildlife Service designates critical habitat in order to protect areas where an endangered species is found and areas with key physical and biological characteristics that will be needed as the species recovers.

(noun)

Used in the following modules: Tracking Endangered Jaguars with Sergio Avila

crust   The uppermost 5-70 km of the earth. There are two types of crust: continental and oceanic. Continental crust ranges from 10-70 km thick and has a composition approximating that of granite. Oceanic crust, on the other hand, is approximately 5 km thick and has a composition similar to basalt, making it significantly denser than continental crust.

Used in the following modules: Earth Structure, Ideas in Science: Theories, Hypotheses, and Laws, Minerals I, Minerals II, Minerals III, Plate Tectonics I, Plate Tectonics II, The Rock Cycle

Crystal   A solid of defined shape that is bound by plane surfaces (facets) that intersect at characteristic angles. The shape of a crystal is defined by the bonding and/or interaction between atoms, ions, or molecules that make up the solid. The substances, planar angles and defects in a crystal affect the electrical and optical properties (including color) of the crystal.

Crystallization   The process through which crystals form, resulting in the change from a liquid or vapor to a solid. Crystallization can happen in two basic ways:
1. By lowering the temperature of a melted material like magma or water, atoms and ions start to aggregate into crystals, forming solid rock or ice. This can also happen from a vapor, as is the case with the formation of snowflakes, but it is much less common.
2. By evaporating water from a solution, the saturation point of the water is reached and a solid begins to precipitate out as crystals (for example, salt flats in the desert have been precipitated out of lakes that dried up).

Curie, Marie   French-Polish physicist and chemist born in Warsaw (1867-1934). Curie was the Head of the Physics Laboratory at the Sorbonne. Working with her husband, Pierre Curie, and inspired by Becquerel’s discovery of radiation, Curie isolated and named the element polonium. She also developed techniques for isolating radium from radioactive residues in order to study its properties. Curie was awarded, with Pierre, half a Nobel Prize in Physics in 1903, for their study of Becquerel radiation. After her husband’s death in 1906, she succeeded him as Professor of General Physics, and was the first woman to hold the post. In 1911 she was awarded a Nobel Prize in Chemistry for her work in radioactivity. For more information see Marie Curie.

Used in the following modules: Nuclear Chemistry

Curie, Pierre   The French physicist born in Paris, France (1859 – 1906 CE). Pioneer in the fields of crystallography, magnetism, and piezoelectricity, he shared the 1903 Nobel Prize in Physics with his wife Marie Curie and with Henri Becquerel for research on the “radiation phenomena.” For further information see: Pierre Curie

Cytoplasm   A clear, water-based gel that contains enzymes, salts and organic molecules. In eukaryotic cells, cytoplasm surrounds the nucleus and organelles. The role of cytoplasm within the cell is to move materials around and to dissolve cellular waste. It is the primary site for chemical activity in the cell.

Used in the following modules: Cells

Dalton, John   English physicist, chemist and meteorologist born in Eaglesfield, Cumberland (1766-1844). Dalton published Experimental Essays on the Constitution of Mixed Gases; on the Force of Steam or Vapour from water and other liquids in different temperatures, both in a Torricellian vacuum and in air; on Evaporation; and on the Expansion of Gasses by Heat, in which he details his theory of partial pressures in gas mixtures. He is most famous for his investigation of relative atomic weights, and for founding atomic theory. For further information see John Dalton.

Used in the following modules: Atomic Theory I, Earth's Atmosphere, Matter, Research Methods: Modeling

Dana, James Dwight   American geologist, mineralogist, and naturalist, born in Utica, New York (1813-1895). Dana published A System of Mineralogy in 1837, which remains a standard in the field. He served as geologist and mineralogist on the U.S. Antarctic and South Seas expedition in 1838-1842. On returning to the states, he published Zoophytes (1846), Geology (1849), and Crustacea (1852-55). He served as coeditor of the American Journal of Science. His other publications include Manual of Geology (1862), Manual of Mineralogy (1843), Corals and Coral Islands (1872), and Characteristics of Volcanoes (1890). For more information see James Dwight Dana.

Used in the following modules: Minerals II

Darwin, Charles   English naturalist and geologist born in Shrewsbury, Shropshire (1809-1882). While serving as naturalist aboard HMS Beagle, Darwin developed his theory of evolution through natural selection based on his detailed observations of species, most famously, the variety of finches. He published his theory in 1859 in his book On the Origin of Species. His other works include The Descent of Man, and Selection in Relation to Sex and The Expression of the Emotions in Man and Animals. For further information, see Darwin Online.

data   (plural form of datum) A collection of pieces of information, generally taking the form of numbers, text, bits, or facts, that are related either by the method in which they are collected or the manner in which they are stored. For more information, see: Data: Analysis and Interpretation

daughter   A material that is derived from the breakdown or division of another. For example, a product of the radioactive decay of an element; or a cell or cells that are derived from the division of a parent cell.

Used in the following modules: Charles Darwin II, Classic Experiment: Meselson and Stahl, Data: Uncertainty, Error, and Confidence, Nuclear Chemistry

Daughter product   In nuclear physics, the decay product of radioactivity.

Used in the following modules: Data: Uncertainty, Error, and Confidence

de Vries, Hugo   Dutch botanist and geneticist, born in Haarlem, Holland (1848-1935). He is known for “rediscovering” Gregor Mendel’s 1850s laws of heredity in the 1890s. Based in part on that rediscovery, he suggested the concept of genes, and developing a theory of evolution based on mutations. For further information, see Hugo de Vries.

Used in the following modules: Genetics II

Decompose   To break up into constituent parts by or as if by a chemical process, to rot.

Used in the following modules: Research Methods: The Practice of Science

Delta   Deltas form where rivers reach lakes, seas, or the ocean, and deposit their remaining sediment in a broad, flat plain as the river slows and eventually stops. The name comes from the Greek letter delta, shaped like a triangle, as these features are often triangular with one point at the river mouth.

Used in the following modules: Research Methods: Modeling, The Rock Cycle

Democritus   Greek natural philosopher born in Thrace (ca. 460-370 BCE). With his teacher, Leucippus, Democritus developed the atomist concept of the cosmos, which held that the world is composed of invisible, minute particles suspended in a void. For further information, see Democritus.

Used in the following modules: Light I, Matter

Denitrification   The loss or removal of nitrogen or nitrogen compounds; specifically: reduction of nitrates or nitrites commonly by bacteria (as in soil) that usually results in the escape of nitrogen into the air.

Used in the following modules: The Nitrogen Cycle

density   A measure of the compactness of a substance given by the mass per unit volume (d = m/v). Common units of density include g/ml, g/cm3, and kg/L. A measure of lead is not heavier than an equivalent measure of styrofoam, it is denser.

Deoxyribonucleic acid   A double-stranded, helical polymer of the sugar deoxyribose, phosphate, and one of four nucleotide bases (Adenine, Cytosine, Guanine, and Thymine). The molecule is the primary carrier of genetic information in all cells.

Used in the following modules: Creativity in Science

Dependent Variable   In science, a dependent variable refers to a condition or parameter that may change as a result of an experimental treatment on an independent variable. The change in the dependent variable is then observed or measured toward understanding the underlying processes involved in the change. For more information, see: Research Methods: Experimentation

Used in the following modules: Research Methods: Experimentation

Descartes, Rene   French mathematician and philosopher born in Indre-et-Loire, France (1596-1650). Descartes invented analytical geometry and developed what is now called the Cartesian coordinate system, which describes geometry in term of algebra. He was an influential philosopher as well, famously stating, “Cogito ergo sum” (I think therefore I am). For further information see Rene Descartes.

Used in the following modules: Light I, Wave Mathematics

Deuterated   The isotopic labeling of a compound that contains hydrogen through the substitution of deuterium for some or all of the hydrogen in the molecule.

Used in the following modules: Scientific Ethics

Deuterium   A stable isotope of hydrogen (written 2H) that contains one neutron in its nucleus and has a natural abundance of 0.015%.

Used in the following modules: Atomic Theory II, Scientific Ethics

Diatomic   A molecule that contains two atoms. All of the non-inert gases occur as diatomic molecules: H2, O2, N2, F2, and Cl2.

Used in the following modules: Chemical Equations

Differential equation   An equation relating a variable that changes over time (referred to as a function), to its rate of change (referred to as its derivative). Many fundamental relationships in the natural world are described by differential equations, for example Newton’s Second Law relates the force on a particle to the rate of change of that particle’s linear momentum: F = d (mv) / dt. In this equation, the force on a particle (F) is equal to the rate of change over time (expressed by the derivative designation d / dt) of the particle’s momentum (which is a product of the particle’s mass [m] and velocity [v]).

Used in the following modules: Research Methods: Modeling

Diffract   To undergo the process of diffraction.

Used in the following modules: Creativity in Science, Light I

Diffraction   The bending or spreading of waves when they meet an obstruction.

Used in the following modules: Creativity in Science, DNA II, Light I, Minerals I, Minerals III, Research Methods: Description

Diffusion   The movement of atoms or molecules from one part of a medium to another caused by their random thermal motion. The result of diffusion is a tendency for particles to move from an area of higher concentration to an area of lower concentration.

Used in the following modules: Absorption, Distribution and Storage of Chemicals

Diorite   An intrusive igneous rock of intermediate composition, often called “salt-and-pepper” rock because of its speckled black and white appearance. The main minerals present are plagioclase and hornblende. Around the world, diorite forms below volcanoes along convergent boundaries, and its extrusive equivalent is andesite.

Used in the following modules: The Rock Cycle

Dipole   An asymmetrical distribution of electrical charge across an object. Polar molecules contain a dipole.

Used in the following modules: Chemical Bonding, Water

Dipole-dipole interaction   An interaction between two or more molecular dipoles resulting from the attraction between oppositely charged ends of the molecules.

Dissociate   The breaking apart of a molecule, especially in the presence of heat or a polar solvent. For example, the ionic compound sodium chloride dissociates in water by separating into positively charged sodium ions and negatively charged chlorine atoms.

divergent boundary   A plate boundary where two plates are moving away from each other.

DNA   Deoxyribonucleic Acid. A double-stranded nucleic acid containing the sugar 2-deoxy-D-ribose. A constituent of cellular nuclear material responsible for encoding genetic information in most organisms. Specifically, a template for the synthesis of proteins and enzymes in most organisms.

DNA Helicase   An enzyme which pulls two strands of DNA apart by unwinding the DNA double helix.

Used in the following modules: DNA III

DNA Ligase   An enzyme that can covalently link two double-stranded piece of DNA together by forming a phosphodiester bond between them.

Used in the following modules: DNA III

DNA Polymerase   An enzyme that is capable of synthesizing DNA molecules through the polymerization of nucleotides.

Used in the following modules: DNA III

Doppler Effect   describes the change in a wave’s frequency experienced by an observer moving in relation to the wave’s source. In the case that the wave source and observer are moving toward one another, the frequency of the observed waves increases and wavelength decreases. With sound, this would result in an increase in pitch. Conversely, for a wave source and observer moving away from one another, the wave frequency decreases and wavelength increases. With sound, this would result in a decrease in pitch. The Doppler Effect can be experienced with any wave form, including light (see redshift and blueshift).

Used in the following modules: The Nature of Scientific Knowledge

Doppler, Christian   (aka Johann Christian Doppler) Mathematician and physicist, born in Salzburg, Austria (1803-1853). Author of On the Coloured Light of the Binary Stars and Some Other Stars of the Heavens (1842), which introduced the principles behind the Doppler Effect and attempted to explain the apparent shift in wavelength of light emitted by a moving star.

Used in the following modules: The Nature of Scientific Knowledge

Earthquake   1. The sudden motion or slip along a fault. 2. The ground shaking that results from the release of seismic energy either by (1) or by other means, such as the movement of magma beneath the surface of the earth.

Eclogite   A metamorphic rock that forms from mafic rocks (like basalt and gabbro) under extremely high pressure. The main minerals present are garnet and a green pyroxene, giving the rock a characteristic, mottled red and green appearance. The most common environment where ecolgites form is deep in subduction zones, where subducted oceanic crust is put under very high pressures.

Used in the following modules: The Rock Cycle

Ecosystem   The complex of a community of organisms and its environment, functioning as a unit.

Used in the following modules: Scientific Communication: The How and Why of Scientific Meetings, Studying Climate Change with Kevin Arrigo, The Nitrogen Cycle

Einstein, Albert   Theoretical physicist, born in Württemberg, Germany (1879-1955) who became an American citizen in 1940. While working as a patent clerk in Zurich, he developed theories on the photoelectric effect and relativity, for which he won a Nobel Prize in physics in 1921. He was also associated with the Manhattan Project, which resulted in the development of the atomic bomb. In 1999, Time magazine named Einstein “Person of the Century.” For further information see Albert Einstein

El Niño-Southern Oscillation   A 2-7 year climatic cycle in the Tropical Pacific. In El Niño years, the trade winds die down, leading to a build-up of unusually warm water in the eastern Pacific Ocean, which results in increased rainfall in the southern United States and Peru and drought in Southeast Asia and Australia. For more information, visit the El Niño Theme Page at the National Oceanic and Atmospheric Association (NOAA).

Used in the following modules: Ideas in Science: Scientific Controversy

Electrical charge   A fundamental property used to explain attraction and repulsion between certain particles. Two types of charge exist: negative charge, which is generally conveyed as an excess of electrons; and positive charge, which is generally conveyed as a lack of electrons and excess of protons. The interaction of opposite charges produces an attractive electrical force, and the interaction of like charges produces a repulsive electrical force.

Used in the following modules: Atomic Theory I, Atomic Theory II, Chemical Bonding, Chemical Reactions, Water

Electrical force   A fundamental force produced by the interaction of electrical charges. Sometimes called the ‘electromagnetic’ force, electrical force is several billion times stronger than gravitational force.

Used in the following modules: Light II

Electrolyte   A substance that dissociates into 2 or more oppositely charged ions in water. Electrolytic solutions conduct electricity because the charged ions can carry electrons in water.

Electromagnetic Radiation   A series of waves that are propagated by simultaneous, periodic variations of electrical and magnetic fields. Examples of electromagnetic radiation include radio waves, light, X-rays, gamma rays and others.

Used in the following modules: Light II

electron   A sub-atomic particle with a negative charge of 1.60 × 10-19 coulombs and a mass of 9.11 × 10-31 kg. Electrons are generally found around the nucleus of an atom, but may be gained or lost during ion formation. Compare to the proton.

Electron shell   The orbitals around the nucleus of an atom where electrons reside. Also called electron orbitals and energy levels.

Used in the following modules: Atomic Theory II, Chemical Bonding, Chemical Reactions, Teaching Effectively with Multimedia, The Periodic Table of Elements

Electronegativity   A relative measure of the affinity (or attraction) that atoms of an element have for electrons. The higher the electronegativity of an atom, the stronger will be its affinity for electrons. The type of bond formed between two atoms (ionic or covalent) can be predicted by the difference in electronegativities of the two bonding atoms.

Element   One of less than 118 pure chemical substances. An element is a substance composed of atoms with identical atomic number.

Empedocles   Greek philosopher born in Acragas (490-430 BCE). He is credited (by Aristotle) with inventing rhetoric, and by the philosopher Galen with founding the science of medicine. Empedocles is remembered for his belief that all matter was composed of four elements: earth, air, fire and water. He also proved experimentally that air was a substance, rather than empty space, and deduced that light travels at a finite velocity. For more information see Empedocles.

Used in the following modules: Matter, Research Methods: Experimentation, Research Methods: The Practice of Science

endangered species list   (Shorthand for the United States' "Federal List of Endangered and Threatened Wildlife and Plants") An official list of species that are at risk of going extinct. The U.S. Fish and Wildlife Service and the National Oceanic and Atmospheric Administration maintain the list and develop plans to help listed species recover by protecting them and their habitat.

Species fall in different categories depending on the urgency of their situation. A species that is officially endangered is on the brink of extinction. A threatened species is likely to be on the brink of extinction in the near future. A candidate species is one that has been studied and is being considered for listing.

Other countries and international bodies have similar designations. CITES (the Convention on International Trade in Endangered Species of Wild Fauna and Flora) has been signed by 175 countries to date. This cooperative agreement regulates trade of endangered plants and animals (and products made from them) in an effort to protect those species globally.

Find out which species are on the endangered species list or protected by CITES.

(noun)

Used in the following modules: Tracking Endangered Jaguars with Sergio Avila

endemic   Natural or native to a particular location or region (usually referring to a species of plant or animal). For example, the Christmas Island red crab is endemic to Christmas Island and the Cocos Islands in the Indian Ocean.

Endocytosis   The uptake by a cell of material from its environment by a process in which the cell surrounds the material and engulfs it with a vesicle formed by its plasma membrane.

Used in the following modules: Absorption, Distribution and Storage of Chemicals

Endothermic   A process or reaction that absorbs heat. For example, ice melting is an example of an endothermic process because it absorbs heat from its surroundings.

Used in the following modules: Chemical Reactions

energy   An abstract property defined as the capacity to do work. The basic forms of energy include chemical, electrical, mechanical, nuclear and radiant (light).

ENIAC   Short for Electronic Numerical Integrator and Computer; the first general-purpose electronic computer. It was the first high-speed, digital computer capable of being reprogrammed to solve a broad range of computing problems.

Used in the following modules: Research Methods: Modeling

ENSO   El Niño-Southern Oscillation, also called "El Niño".

Entropy   depending on context, refers to either: 1) the measure of unusable energy within a closed system during energy conversion, or 2) the measure of disorder or randomness in a system.

Used in the following modules: Energy, The Nature of Scientific Knowledge

Environmental Protection Agency   An independent federal agency of the United States government established to coordinate programs to reduce pollution and protect the environment.

Used in the following modules: The Nitrogen Cycle

Enzyme   Molecules produced by living organisms that help catalyze biochemical reactions. Enzymes are predominantly protein or protein-based molecules and are highly specific in their mechanism of action as well as the reactants that they work upon (called substrates).

Used in the following modules: Carbohydrates, DNA I, DNA III, Fats and Proteins

Used in the following modules: Scientists and the Scientific Community

Epidemiology   The scientific study of epidemics and epidemic diseases, especially the patterns, causes, and control of diseases in human populations.

Used in the following modules: Data: Statistics, Research Methods: Comparison

Epistemology   (from the Greek episteme, ‘knowledge’, and logos, ‘theory’) the study of the nature of knowledge; a branch of philosophy investigating the origin, nature, methods, and limits of human knowledge.

Erosion   The action or process of eroding: wearing away by the action of water, wind, glacial ice, etc.

Used in the following modules: Ideas in Science: Theories, Hypotheses, and Laws, The Rock Cycle

Eugenics   A social philosophy that advocates for the control of heritable characteristics in humans through various forms of intervention including selective breeding, sterilization, and others.

eukaryote   a single- or multi-cellular organism whose cells contain a distinct nucleus that encloses the organism’s genetic material.

Evolution   change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and genetic drift.

Excited State   An energy state for an atom in which electrons exist above the minimum or ground state configuration. In general, excited states are unstable and will quickly relax back to ground state through the emission of a quantum of energy.

Exothermic   A process or reaction that releases heat. For example, wood burning in the presence of oxygen is an example of an exothermic reaction.

Used in the following modules: Chemical Reactions

extensive property   A property of matter that is dependent on the amount of material present. Common extensive properties include mass, volume, length and charge.

extinction   The complete and permanent loss of all individuals of a species of organism.

(noun)

Used in the following modules: Charles Darwin III, Ideas in Science: Theories, Hypotheses, and Laws, Scientific Communication: Utilizing the Scientific Literature

extrapolate   (Mathematics) Using trends or patterns identified within a data set to estimate the value of variables outside the range of the original data.

(General Science) To make an estimate, form a hypothesis, or draw a conclusion about an unknown situation by applying trends seen or evidence discovered in a similar situation. For example, if scientists document that a certain species' population has declined in one area because of a rise in temperature, they may be able to extrapolate (or make a prediction) about how the species will respond to a rise in temperature in another location.

(verb)

Used in the following modules: Tracking Endangered Jaguars with Sergio Avila

extrusion   A process by which viscous magma is emitted from below the surface of the earth to cool on the surface.

Used in the following modules: Plate Tectonics I

Fahrenheit, Daniel Gabriel   German physicist born in Danzig, Poland (1686-1736). Fahrenheit invented the alcohol thermometer in 1709, and the mercury thermometer in 1714. He also developed the temperature scale now known as Fahrenheit, which defines freezing as 32°F, boiling as 212°F, and body temperature as 98.6°F. For more information see Daniel Gabriel Fahrenheit.

Used in the following modules: Data: Analysis and Interpretation, Temperature

Faraday, Michael   British chemist and physicist born in London (1791-1867). In 1831, Faraday discovered electromagnetic induction, the principle by which electric transformers and generators function. The farad, a unit of electrical capacitance, is named in his honor. For further information, see Michael Faraday.

Used in the following modules: Light II

Fermat, Pierre   A French lawyer and mathematician, born in Beaumont-de-Lomagne (1602-1665 CE). Fermat had a very successful career in the criminal court, but retained a deep interest in mathematics. He made contributions toward the development of calculus and analytical geometry; and along with Blaise Pascal he laid the foundations of probability theory which led to development of statistical methods. For further information see Pierre de Fermat; also see our module Data: Statistics.

Used in the following modules: Wave Mathematics

Feynman, Richard   American physicist, born in Queens, New York (1918-1988). Feynman is best known for his work on quantum mechanics, quantum electrodynamics, and particle theory. In 1965, he was the joint recipient of the Nobel Prize in physics (with Julian Schwinger and Shin-Ichiro Tomonaga) for his work on quantum electrodynamics. Feynman also worked on the Manhattan Project, and participated on the panel that investigated the Space Shuttle Challenger disaster. In addition, he published several popular semi-autobiographical books. For further information see Richard Feynman.

Filial   In science, filial is commonly used to designate the sequence of generations following the parental generation. For example, the first filial generation (abbreviated as F1) would be the direct offspring of a parental generation, the second filial generation (F2) would be the offspring of the first filial generation.

Used in the following modules: Genetics I

First Law of Thermodynamics   One of three Laws of Thermodynamics, or laws relating to heat power. The First Law explores the conservation of energy. Specifically, this law explains that energy cannot be created or destroyed, only transformed from one form to another. It also states that the energy within a closed system is fixed – it cannot increase or decrease. The First Law is often expressed as an equation: ∆U = Q - W, or the change in internal energy (∆U) equals the heat added to the system (Q) minus the work done by the system (W). See also the Second Law of Thermodynamcis and the Third Law of Thermodynamics.

Used in the following modules: Energy

Fisher, Ronald   English statistician, geneticist and evolutionary biologist born in London (1890-1962). He is considered the father of modern statistics. In 1919, Fisher began working at the Rothamsted Experimental Station. Six years later, he published Statistical Methods for Research Workers, drawing on his experience in creating statistically valid experiments. In 1935, Fisher published The Design of Experiments. Both works are still considered standards in the field of statistics. Fisher also contributed extensively to understanding population genetics, and was a staunch promoter of eugenics. For further information see Ronald Fisher.

Used in the following modules: Research Methods: Comparison, Research Methods: The Practice of Science

Fixity of Species   An idea popular among 16th and 17th century European zoologists and botanists that reflected Western religion and the story of creation as laid out in the Bible. A key feature of the argument for "fixity" was the notion that the structure of each species was based on a model, ideal form and never changed. With the publication of Darwin’s and other scientists’ work on evolution, the idea is no longer considered by scientists. For more information, see our module Charles Darwin I.

Used in the following modules: Charles Darwin I, Ideas in Science: Theories, Hypotheses, and Laws, Scientists and the Scientific Community

Floodplain   The relatively flat land adjacent to a river channel that is underwater when the river floods. The floodplain is the site of deposition of sediments carried down the river and are often occupied by farms, due to the proximity of irrigation water, fertile soils, and flat topography.

Used in the following modules: The Rock Cycle

folk taxonomy   The names given to organisms and phenomena on the basis of cultural tradition as opposed to scientific study.

Used in the following modules: Taxonomy I

force   An influence (a “push or pull”) that changes the motion of a moving object (e.g. slows it down, speeds it up, changes its direction) or produces motion in a stationary object. The strength of a force is calculated by multiplying the mass of the object by its acceleration. In the metric (or SI) system, force is measured in newtons.

Franklin, Benjamin   American inventor, scientist, and politician, born in Boston (1706-1790). Franklin was a prolific scientist and humanitarian. In Philadelphia, he founded America’s first subscription library, the city hospital, and the American Philosophical Society. He was also an inventor, designing a heat-efficient stove, swim fins, and bifocals. His experiments with electricity and lightening brought him global recognition. In the political scene, he was elected to the continental congress, signed the Declaration of Independence, and—one of his last acts before dying—wrote an antislavery treatise. For further information see Benjamin Franklin.

Franklin, Rosalind   English biophysicist and x-ray crystallographer born in London (1920-1958). Franklin discovered that DNA crystallizes into two forms, and, working with Maurice Wilkins, used x-ray crystallography to determine the molecular structure of one of these forms. Her work was instrumental in allowing James Watson and Francis Crick to determine the complete structure of DNA. Her results were shared with them without her knowledge, and her contributions were not acknowledged. When Watson, Crick and Wilkins won a Nobel Prize for their work on the structure of DNA in 1962, Franklin was again overlooked, because the Nobel Prize cannot be awarded posthumously. For further information see Rosalind Franklin

Used in the following modules: Creativity in Science, DNA II

Frequency   The rate at which a vibration occurs that constitutes a wave, either in a material or in an electromagnetic field, usually measured in hertz (Hz).

Gabbro   A dark-colored intrusive igneous rock that consists mostly of the minerals plagioclase, pyroxene, and olivine. Gabbro has a similar composition to basalt, which is extrusive. Both gabbro and basalt are mafic rocks, composed of minerals high in iron and magnesium.

Used in the following modules: The Rock Cycle

Galileo Galilei   The Italian physicist, mathematician, and astronomer born in Pisa in the Grand Duchy of Tuscany (1564-1642 CE). Among other things, Galileo studied the acceleration of objects and discovered the four largest moons of the planet Jupiter. His work significantly advanced the use of quantitative experimentation in science, and he made noteworthy contributions in the development of technology: he invented the refracting telescope, perfected the compound microscope, and improved compass design. Galileo was famously jailed during the Inquisition for his support of Copernicus’s heliocentric view of the cosmos. For further information see Galileo Galilei

Used in the following modules: Gravity, Research Methods: The Practice of Science, Scientific Institutions and Societies, Temperature, Waves and Wave Motion

Gamete   A reproductive cell having half the number of chromosomes (a haploid) of a mature cell, e.g. a sperm or egg cell.

Used in the following modules: Genetics I

Used in the following modules: Research Methods: Modeling

Gene   Material (usually DNA) that is inherited from a parent and which encodes for a cellular component important for some cellular function.

General Circulation Model   Also referred to as General Climate Models; a class of computer models used for weather forecasting, and understanding or projecting climate change. GCM's designed for applications on the scale of decades to centuries were originally created by Syukuro Manabe and Kirk Bryan at the Geophysical Fluid Dynamics Laboratory in Princeton, New Jersey. For more information, see: Research Methods: Modeling

Used in the following modules: Research Methods: Modeling

Genotype   the genetic makeup of an organism or group of organisms; the genetic description of an individual. Genotype may refer to a single gene, a set of genes, or the entire genetic makeup of an individual.

Used in the following modules: Genetics I, Genetics II

genus   A taxonomic category one rank or step above Species in the Linnaean system, and which may include one or many species in it.

Used in the following modules: Adaptation, Charles Darwin III, From Stable Chromosomes to Jumping Genes, Taxonomy II: Nomenclature, The Nitrogen Cycle

Geocentric   Having or representing the Earth as the center, as in the heliocentric concept of the universe. Compare to heliocentric.

Used in the following modules: Research Methods: The Practice of Science

geographic information system   (GIS) A set of computer-based tools used to collect, store, analyze, and map data that has a location-based or spatial component, such as latitude and longitude. The term GIS usually includes computer software and hardware, data collectors, and the data itself.

These systems allow researchers and decision makers to compile information from many different sources. By gathering and mapping a wide variety of data, we can see new trends and relationships. Satellite images, records of soil type or vegetation cover, census data, locations of roads and schools, and many other types of data can be compiled in a GIS.

For more detailed information about GIS and its many uses, visit the U.S. Geological Survey.

(noun)

Used in the following modules: Tracking Endangered Jaguars with Sergio Avila

Geological Society of America   A professional society established in 1888 focused on geosciences. The mission of the Geological Society of America is “to be a leader in advancing the geosciences, enhancing the professional growth of its members, and promoting the geosciences in the service to humankind and stewardship of the Earth.” GSA hosts an annual meeting and several section meetings every year and publishes several journals. More information about GSA can be found at their website.

Used in the following modules: Research Methods: Description, Scientific Communication: The How and Why of Scientific Meetings

Geosphere   The solid portion of Earth, including the crust and mantle.

Used in the following modules: Studying Climate Change with Kevin Arrigo, The Carbon Cycle, The Nitrogen Cycle

Gilbert, Grove Karl   American geologist born in Rochester, New York (1843-1918). Gilbert participated in the Wheeler geologic survey of the American West. His field studies resulted in the publication on The Geology of the Henry Mountains, which established his preeminence as a geologist. In 1879, he was appointed the Senior Geologist at the newly created U.S. Geological Survey. In addition to his study of the Henry Mountains, Gilbert investigated the Pleistocene Lake Bonneville. He is considered a major founder of the field of geomorphology, having investigated and published on erosion, river incision and sedimentation. For further information see Grove Karl Gilbert.

Used in the following modules: Research Methods: Description, Research Methods: The Practice of Science

Glacial period   Any of those parts of geologic time from Precambrian onward when a much larger portion of the earth was covered by glaciers than at present.

Used in the following modules: The Carbon Cycle

Global Positioning System   (GPS) A system of satellites maintained by the U.S. government that provides people with highly accurate information about their location on the Earth (within about three meters) and how to navigate from place to place. Users obtain the information (called coordinates) using GPS receivers, such as handheld devices, navigation systems in cars, and programs like Google Maps.

For more detailed information about the system and its parts, visit the U.S. government’s GPS information center. For more information about other countries' global navigation satellite systems, such as Russia’s GLONASS and Europe’s forthcoming Galileo, visit the GPS international cooperation page.

(noun)

Used in the following modules: Plate Tectonics I

glossary terms   Terms highlighted in red in the main lesson text are hyperlinked to a pop-up glossary to provide easy access to definitions.

Used in the following modules: Authoring Modules I, Visionlearning, Visionlearning Teaching Modules

Goodall, Jane   English primatologist and anthropologist, born in London (1934-). Goodall is famous for her ground-breaking 45-year study of chimpanzee family and social interactions in the Gombe Stream National Park, Tanzania. She founded the Jane Goodall Institute and remains a leader in global effort to protect chimpanzees. Goodall revolutionized the field of primatology by discovering tool-making among wild chimpanzee populations, and remains the only human ever accepted into chimpanzee society. Interestingly, Goodall suffers from prosopagnosia, a neurological condition that makes it difficult for her to recognize human faces. For further information, see Jane Goodall.

Gordon, Neil   (1886-1949) An American chemist and science educator. Gordon is most famous for his dedication to communicating science. He founded and was the first editor of the Journal of Chemical Education, published by the American Chemical Society, and established the Gordon Research Conferences, a venue to bring scientists together to discuss research on the frontiers of knowledge.

Used in the following modules: Scientific Communication: The How and Why of Scientific Meetings

Gould, Stephen Jay   American paleontologist born in New York City, New York (1941-2002). With Niles Eldridge, he co-created and championed the concept of evolution via punctuated equilibrium, and wrote many popular books about evolution, paleontology, and the history of science. For further information see Stephen Jay Gould.

Used in the following modules: Ideas in Science: Theories, Hypotheses, and Laws

Granite   A light-colored, coarse-grained igneous rock formed by cooling of silica-rich magma below the surface of the earth. Granite is considered to be the average composition of the continental crust of the earth.

Used in the following modules: Earth Structure, Minerals I, Minerals II, Minerals III, Scientific Communication: Utilizing the Scientific Literature

Greenhouse effect   The greenhouse effect is created by gases like carbon dioxide in the earth's atmosphere. Carbon dioxide and other greenhouse gases allow radiation from the sun to pass through the atmosphere; the earth then absorbs this radiation and emits heat. That heat is absorbed by the
greenhouse gases, resulting in atmospheric warming.

Used in the following modules: Earth's Atmosphere

Greenhouse gas   A greenhouse gas is a component of the atmosphere that absorbs heat radiated by the earth and subsequently warms the atmosphere, creating what is commonly known as the greenhouse effect. Common greenhouse gases include carbon dioxide (CO2), methane (CH4), water vapor, amd sulfate (SO4).

Used in the following modules: Data: Analysis and Interpretation, Research Methods: Comparison, The Nitrogen Cycle

Griffith, Frederick   (c. 1879 - 1941) A British microbiologist whose research focused on the epidemiology and pathology of bacterial infectious diseases. In 1928, Griffith published his most famous paper, which contained the first widely accepted demonstrations of bacteria changing form and function. His experiments showed the bacteria Streptococcus pneumoniae transforming from one strain to another. His findings encouraged other researchers to try to identify the mechanism by which this change could occur; eventually this research led to the discovery of DNA.

Used in the following modules: DNA I

Ground State   The lowest energy state for an atom or molecule. When an atom is in its ground state, its electrons fill the lowest energy levels before they begin to occupy higher orbitals.

Used in the following modules: Atomic Theory II, Teaching Effectively with Multimedia

ground truth   [Verb] To gather data onsite in order calibrate a model or determine whether information captured remotely (such as imagery or measurements taken by satellite) is being accurately interpreted. This often involves going to a location "on-the-ground" or in the field to compare actual characteristics, such as vegetation cover or temperature readings, with characteristics predicted by a model or interpreted from an image. This technique is commonly used with aerial and satellite imagery, remote sensing, meteorology models, and GIS.

[Noun] Data collected at a study site, as opposed to information collected remotely or predicted by a model.

Groundwater   Water that fills pore space in rocks and sediments and forms a subsurface aquifer. Groundwater is distinct from soil moisture, which does not completely fill pore spaces and is immediately beneath the surface.

Used in the following modules: Research Methods: Modeling, The Hydrologic Cycle, The Nitrogen Cycle, The Rock Cycle

Gutenberg, Beno   German geophysicist, born in Darmstadt (1889-1960). Gutenberg is best known for precisely determining the depth to the core of the Earth and describing its elastic properties. He also described the differences in structure of oceanic and continental crust, discovered a low-velocity zone within the mantle, created a magnitude scale for earthquakes, and studied the distribution of temperature in the Earth. For further information, see Beno Gutenberg.

Used in the following modules: Earth Structure

Haber, Fritz   German chemist born in Breslau (1868-1934). Haber began his career in chemistry with investigations on the decomposition and combustion of hydrocarbons. In 1898, he published his textbook Electrochemistry, and followed this with increasing investigations of electrochemical phenomena. Among these experiments, he researched the electrolysis of solid salts, and energy loss by steam engines. In 1918, Haber was awarded a Nobel Prize in Chemistry for his research on nitrogen fixation from the air, a key component in the development of nitrogen fertilizers. For further information see Fritz Haber.

Used in the following modules: The Nitrogen Cycle

habitat   The place or type of environment where a wild plant, animal, or other organism naturally lives or grows.

(noun)

Half-life   The time required for half of the original amount of a substance to undergo a process. For example, the time required for half of the atoms of a radioactive substance to undergo decay; or the time required for half of a ingested substance to be excreted from the body.

Used in the following modules: Nuclear Chemistry

Halley, Edmund   English astronomer born in Derbyshire (1656-1742). He observed transits of Mars and Venus to determine the distance from the Earth to the Sun, and accurately predicted the return of a comet, now named after him. For further information see Edmund Halley.

Used in the following modules: Gravity, Scientific Communication: Utilizing the Scientific Literature

Hau, Lene   Danish physicist born in Vejle (1959-). Her most famous work consisted of experiments in slowing down light. In 1999, she and several colleagues succeeded in slowing light to 17 m/s, and in 2001, they managed to very briefly stop a light beam. In 2007, she and her research team transformed light into matter and back into light using Bose-Einstein condensates. For further information, see Lene Hau.

Used in the following modules: Research Methods: Experimentation

Hawking, Stephen   British cosmologist and theoretical physicist, born in Oxford (1942-). His most important contributions to science have been his study of quantum gravity and black holes. He also authored the extremely popular A Brief History of Time, which spent 237 weeks on the British Sunday Times best-sellers list. Hawking suffers from amyotrophic lateral sclerosis, a degenerative motor neural disease, which was diagnosed during his graduate studies. He is confined to a wheelchair and speaks through a voice-box. As part of an ongoing effort to popularize science and space-travel, Hawking went on a sub-orbital flight, during which he became the first quadriplegic to experience antigravity.
For further information see Stephen Hawking

Used in the following modules: Scientific Communication: Peer Review, Scientific Institutions and Societies

Heat   A measure of the total internal energy of a substance that can be increased or decreased when objects with different temperatures are placed into contact. Heat is a process, not a property of a material.

Heliocentric   Having or representing the sun as a center, as in the heliocentric concept of the universe. Compare to geocentric.

Used in the following modules: Research Methods: The Practice of Science

Heraclitus   A Greek philosopher from Ephesus (535-475 BCE). His philosophy consisted of a belief that everything is in a constant state of flux, and that opposites are not only necessary in life, because they provide balance, but are also, in fact, identical. For further information see Heraclitus.

Used in the following modules: Energy

Herschel, John   Scottish astronomer born in Slough (1792-1871). Herschel studied double star systems, made a comprehensive map of the celestial Southern hemisphere, and was a pioneer and strong proponent of the use of photography in astronomy, now a staple of astronomical research. His book Outlines of Astronomy was a standard textbook for decades after its publication, and the modern New General Catalog (the best-known catalogue of deep sky objects in amateur astronomy) is derived largely from his General Catalogue of Nebulae and Clusters. For more information, see John Herschel.

Used in the following modules: Data: Using Graphs and Visual Data

Herschel, William   English astronomer and composer born in Hanover, Germany (1738-1822). Hershcel worked closely with his sister, Caroline. Their most important contribution was the discovery, in 1781, of the planet Uranus. They also discovered two moons of Uranus in 1787, and two of Saturn’s moons. William Herschel’s work on double stars showed that gravity acts outside of the solar system. He also studied sunspots and their connection to weather. For further information see William Herschel.

Hershey, Alfred   (December 4, 1908 – May 22, 1997) An American bacteriologist and geneticist. His most famous contribution to science was the Hershey-Chase blender experiment, which he and Martha Chase performed, the results of which supported the idea that genetic material is made up of DNA, not protein. In 1962, Hershey was awarded the Nobel Prize in Physiology or Medecine (shared with two other researchers) for work on the genetic structure and replication of viruses.

Used in the following modules: DNA I

Hess, Harry   American marine geologist born in New York, New York (1906-1969). Hess was key scientist in the establishment of the theory of plate tectonics in the early 1960’s. From observations he made of the sea floor while serving in the U.S. Navy during World War II, he developed the idea of sea-floor spreading, which he published in 1962 in the paper “History of Ocean Basins.” For more information see Harry Hess.

Used in the following modules: Plate Tectonics I, Plate Tectonics II

Heterogeneous mixture   A mixture of two or more substances that can be easily separated by common physical means (i.e. settling, filtration, etc.). A mixture in which the components can be visibly distinguished. For example, oil and water. Compare to homogeneous mixture.

heterozygous   having two different alleles for a given gene.

Used in the following modules: Genetics I, Genetics II

Hipparchus   Greek astronomer, mathematician and geographer born in Nicaea (ca. 190-120 BCE). Hipparchus made the oldest surviving quantitative and accurate models for the motion of the Sun and Moon. He also developed a method for accurately predicting solar eclipses and compiled the first comprehensive star catalogue of the western celestial hemisphere. For further information, see Hipparchus.

Used in the following modules: Research Methods: Description, Wave Mathematics

Homeothermic   Of, or pertaining to, the maintenance of a uniform temperature regardless of the temperature of the surroundings. In biology, synonymous with warm-blooded.

Used in the following modules: Adaptation

Homogeneous mixture   A mixture of two or more substances that cannot be easily separated by common physical means (i.e. settling, filtration, etc.). A mixture with no visible separation between its components. For example, salt and water. Compare to heterogeneous mixture.

homozygous   having two identical alleles for a given gene.

Used in the following modules: Genetics I

Hooke, Robert   An English physicist, born on the Isle of Wight (1635-1703). Hooke’s studies were extremely diverse, encompassing biology, geology, physics, chemistry, and astronomy. He was also an accomplished inventor: he designed the universal joint, the iris diaphragm, and a prototype of a respirator, and the balance spring. In 1662, he became the first Curator of Experiments for the Royal Society of London. Hooke discovered the theory for combustion and devised an equation for elasticity, which is now known as Hooke’s Law. He also made important contributions in biology by describing and naming cells, which he observed with a compound microscope that he designed. For further information see Robert Hooke.

Used in the following modules: Cells, Gravity, Light I, Research Methods: Experimentation, Scientific Institutions and Societies

horticulture   the science and art of cultivating plants.

Used in the following modules: Genetics II

hot spot   A fixed plume of hot magma which rises through the mantle and creates volcanoes on the earth’s surface. The Hawaiian Island chain is an example of a hot spot. Because the plumes are fixed, the hot spots record past plate motions.

Hubble Constant   (H0) a numerical value of the expansion factor of the universe. In 1929, Hubble identified this value as 500 km/sec/Mpc (kilometers per second per megaparsec). Today, this value has been refined (as a result of extensive research) to range from 45-90 km/sec/Mpc.

Used in the following modules: The Nature of Scientific Knowledge

Hubble, Edwin Powell   Astronomer, born in Missouri, United States (1889-1953). Author of The Observational Approach to Cosmology and The Realm of the Nebulae (1935). Hubble was the first individual to demonstrate the existence of galaxies outside of our own. He also used Vesto Slipher’s redshift data to show that the degree of redshift increases with distance, thus providing evidence that the universe is expanding. He discovered the asteroid 1373 Cincinnati.

Hudson, Henry   (1560?-1611?) An English sea explorer and navigator in the early 17th century. While searching for the Northwest Passage to India, he explored and mapped the region around what is now New York City, and named Hudson Bay and Hudson River after himself. Hudson made four voyages in search of alternate routes to India, in 1607, 1608, 1609, and 1610. On his last voyage, his ship became trapped in ice in James Bay in the fall of 1610, and had to winter over. Hudson wanted to continuing exploring when the spring thaw freed the boat, but his crew mutinied. Hudson, his son, and six others were cast adrift in a small, open boat, never to be heard from again.

Used in the following modules: Taxonomy I

Human Genome Project   The U.S. Human Genome Project was a major scientific effort funded by the National Institutes of Health and the U.S. Department of Energy. It began in 1990 with the scientific goals of identifying all of the genes in the human genome (approximately 25,000 total) and sequencing all 3 billion base pairs. Other major components of the project involved devising appropriate data storage and analysis tools for the information, and addressing the legal and ethical implications of the scientific work. The project, expected to last fifteen years, was completed in 2003, two years ahead of schedule. For more information, see the Human Genome Project website.

Used in the following modules: Creativity in Science, Data: Analysis and Interpretation

Hurricane   Also called tropical cyclone; “hurricane” is the name used more commonly for tropical cyclones in the northern Atlantic Ocean basin and the eastern Pacific Ocean basin (“typhoon” is used commonly in the western Pacific). An intense, cyclonic storm that forms over warm, tropical ocean waters and then moves west and northeast. To reach hurricane status, sustained wind speeds must reach 73 mph, but they may reach up to 230 mph near the center of the storm.

Used in the following modules: Ideas in Science: Scientific Controversy, Scientific Institutions and Societies, The Process of Science

Hutton, James   Scottish geologist, chemist and naturalist born in Edinburgh (1726-1797). Hutton is considered to be the father of modern geology. From his geologic observations, Hutton became convinced that the Earth was older than the bible suggested. He also belonged to the uniformitarian school of thought, which held that changes to the Earth’s surface did not happen in sudden catastrophes, but rather occurred slowly, by processes that were continuously in effect. In 1795, he published his ideas in The Theory of the Earth, which was later popularized by John Playfair. For further information see James Hutton.

Used in the following modules: Ideas in Science: Theories, Hypotheses, and Laws, The Rock Cycle

Huxley, Thomas Henry   English biologist born in Ealing, Middlesex (1825-1895). While serving in the Navy as an assistant surgeon, Huxley collected and studied marine invertebrates. He was so fierce a proponent of Darwin’s theory of evolution by natural selection that he earned the nickname “Darwin’s Bulldog”. Huxley’s most famous work is Evidence on Man’s Place in Nature, published in 1863, which is the first attempt to apply the concept of evolution to the human race. For further information see Thomas Henry Huxley.

Used in the following modules: Charles Darwin I, Research Methods: Comparison

Huygens, Christian   Dutch mathematician born in The Hague, (1629-1695). Huygens ground and polished his own telescope lenses, and in 1655, he detected the first moon of Saturn using one of them. He also proposed the theory that Saturn has rings. Huygens worked on a variety of other mathematical, scientific, and engineering problems, including the development of accurate pendulum clocks and gravitational theory. In 1678, he published his “Theory of Light” in which he argued that light is a wave, not a particle. For further information see Christian Huygens.

Used in the following modules: Light I

hybrid   the offspring of two plants or animals of different breeds, varieties, species, or genera. Hybrid often refers to plants or animals produced through selective breeding for specific genetic characteristics, such as plants that are bred to be drought resistant, or sheep that are bred to produce softer wool.

Used in the following modules: Genetics I, Genetics II, Research Methods: Comparison

Hydrocarbon   An organic compound that contains only hydrogen and carbon.

Used in the following modules: Organic Chemistry

Hydrogen bond   A strong dipole-dipole attraction between two or more molecules, at least one of which has a hydrogen atom bonded to an electron-withdrawing atom. More specifically, a weak bond formed between a hydrogen atom on one molecule which has developed a partial positive charge because of its bonding to an electronegative atom (commonly N, O, or F) and an electronegative atom on another molecule.

Used in the following modules: Carbohydrates, Classic Experiment: Meselson and Stahl, DNA II, DNA III, Matter: States of Matter, Minerals II, Water

Hydrophilic   Literally meaning water loving, a substance that readily associates with water. Often polar molecules or some ionic molecules that easily dissolve in or form solutions with water. Compare to hydrophobic.

Hydrophobic   Literally meaning water fearing, a substance that has little affinity for water. Generally, non-polar molecules that do not dissolve in or form solutions with water. Compare to hydrophilic.

Used in the following modules: Fats and Proteins

Hydroxyl   An -OH group within a molecule.

Used in the following modules: Organic Chemistry

Hypothesis   From the Greek word hypothesis meaning assumption or the basis of an argument, a hypothesis is a proposal intended to explain certain observations or phenomenon. In science, hypotheses represent the basis of scientific research, which is pursued to objectively determine whether or not a hypothesis is correct. For more information, see: Ideas in Science: Theories, Hypotheses, and Laws

Igneous   Formed from the cooling and crystallization of a magma. Igneous rocks can be extrusive, meaning that they cooled on or very near the earth’s surface, or intrusive, meaning that they cooled below the earth’s surface.

Used in the following modules: Minerals III, Research Methods: Description, The Rock Cycle

Independent Variable   In science, an independent variable is a condition or parameter that is consciously manipulated in some way in the course of scientific research with the goal of observing the outcome of this manipulation on a second variable, referred to as a dependent variable. For more information, see: Research Methods: Experimentation

Used in the following modules: Research Methods: Experimentation

Inert   Deficient in active properties; especially: lacking a usual or anticipated chemical or biological action.

Used in the following modules: Chemical Reactions, Research Methods: The Practice of Science, The Nitrogen Cycle

intensive property   A property of matter that is independent of the amount of material present. Common intensive properties include boiling point, color, density, melting point, and solubility.

Used in the following modules: Density

interdisciplinary   Relating to or drawn from more than one branch of science or knowledge. For example, an interdisciplinary research team studying climate change might have an environmental scientist, a computer programmer, a chemist, and an economist.

Used in the following modules: Authoring Modules I, Data: Analysis and Interpretation, The Carbon Cycle, Visionlearning, Visionlearning Teaching Modules

Interglacial period   Any of those parts of geologic time from Precambrian onward when a similar or lesser portion of the earth was covered by glaciers than at present.

Used in the following modules: The Carbon Cycle

Intergovernmental Panel on Climate Change   A scientific body created to evaluate the risk of human-caused climate change. The panel was established in 1988 by two organizations of the United Nations, the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP).

Used in the following modules: Data: Analysis and Interpretation, Data: Using Graphs and Visual Data, Research Methods: Comparison, The Carbon Cycle

Interstitial   Pertaining to or located between the small spaces and gaps between tissues in an organism.

Invertebrate   an organism without a backbone. Invertebrates account for 95-99% of all animal species on Earth and include organisms like worms, insects, and mollusks.

Used in the following modules: Adaptation, Ideas in Science: Theories, Hypotheses, and Laws, Studying Climate Change with Kevin Arrigo

ion   An atom or molecule that has acquired an electrical charge by either gaining or losing electrons. A cation is an ion that has lost electrons and acquired a positive charge. An anion is an ion that has gained electrons and acquired a negative charge.

Ionic bond   A chemical bond characterized by electrostatic attraction between ions of opposite charge. The formation of an ionic bond involves a complete transfer of electrons between atoms, and can be predicted when one bonding atom has a much higher electronegativity than the other. Compare to covalent bond, hydrogen bond.

Used in the following modules: Chemical Bonding

Ionic compound   A chemical compound held together by ionic bonds, that is, electrostatic attraction between positive and negative ions. Ionic compounds generally form ordered structures in which each cation is surrounded by several anions and vice versa. Thus ionic compounds commonly form complex lattices rather than true molecules.

Used in the following modules: Chemical Bonding, Water

Used in the following modules: Data: Analysis and Interpretation

Isomers   Molecules with identical molecular formulas but differing in the sequence of bonding or arrangement in space of their atoms, i.e. their structural formulas.

Used in the following modules: Organic Chemistry

Isotope   Atoms of the same element with different numbers of neutrons in their atomic nucleus. Isotopes have the same chemical properties and atomic number but different atomic masses. Isotopes can differ greatly in nuclear stability.

Iteration   One step in an iterative process. Iteration refers to a single component of a process in which multiple, repeating steps are used to determine a solution.

Used in the following modules: Data: Uncertainty, Error, and Confidence

Iterative   Repetitive in a cyclical fashion. An iterative process or method in science is one in which a sequence of steps is repeated in order to solve a problem, and each repetition of the steps brings one closer and closer to the solution. For more information, see: Data: Uncertainty, Error, and Confidence

Used in the following modules: Research Methods: Description, Research Methods: Modeling, Scientific Communication: Utilizing the Scientific Literature

Joliot-Curie, Frederic   The French physicist born in Paris, France (1900 – 1958 CE). Shared the 1935 Nobel Prize in Chemistry with his wife Irène Joliot-Curie for their discovery of artificial radioactivity. For further information see: Frederic Joliot-Curie

Joliot-Curie, Irene   The French scientist born in Paris, France (1897 – 1956 CE). Daughter of Marie Curie and Pierre Curie, Irène shared the 1935 Nobel Prize in Chemistry with her husband Frédéric Joliot-Curie for their discovery of artificial radioactivity. For further information see: Irene Joliot-Curie

joule   A metric (or SI) unit measuring energy or work and named for the British scientist James Prescott Joule. One joule (J) represents the amount of work that can be done by a force of one newton (N) acting over a distance of one meter (m):

J = 1 N·m  or  J = 1 kg·m2/s2.

(noun)

Used in the following modules: Energy

Joule, James Prescott   English physicist born in Salford (1818-1889). In 1840, Joule published a paper detailing what is now called Joule’s Law, which describes the relationship between the current through a resistor and the heat lost from the system. He continued his studies on heat and its relationship to mechanical work, concluding that heat is a form of energy. He developed the theory of conservation of energy, and, subsequently, the first law of thermodynamics. The joule, an SI unit of energy, is named after him. For further information see James Prescott Joule.

Used in the following modules: Energy

Keeling, Charles   American marine geochemist born in Scranton, Pennsylvania (1928-2005). Keeling researched the greenhouse effect and subsequent changes in the earth’s atmosphere. Keeling helped establish a station on Mauna Loa in 1958 where monthly atmospheric CO2 measurements have been taken ever since. His dedication to producing a long-term record was critical to showing that atmospheric carbon dioxide levels have been increasing over time. His work resulted in a greater awareness of the human impact on global climate. For further information see Charles David Keeling.

Used in the following modules: Research Methods: Comparison, Research Methods: Description, The Carbon Cycle

Kelvin, William   Scottish physician and mathematician born in Belfast, Ireland (1824-1907). In 1867, Kelvin published Treatise on Natural Philosophy (later republished as Principles of Mechanics and Dynamics), which established the role of energy in the theory of mechanics. Kelvin also championed the idea that the entropy of the universe constantly increases, and will eventually reach a state of uniform temperature and maximum entropy, where no further work is possible: this uniform temperature will be absolute zero, or 0° Kelvin (-273°C). For more information, see William Kelvin.

Used in the following modules: Temperature

Kepler, Johannes   German mathematician and astronomer born in Weil der Stadt, Württemburg (now part of Stuttgart, Germany) (1571-1630). Kepler is best known for outlining his laws of planetary motion, which defined the paths of the planets as orbits that could be mathematically represented as an ellipse. He was a champion if the Copernican model of the universe, publishing the Mysterium Cosmographicum in defense of it. For further information, see Johannes Kepler

Used in the following modules: Gravity, Research Methods: The Practice of Science

Kinetic Energy   The energy an object possesses by virtue of its motion.An object of mass m moving at velocity v has a kinetic energy of ½m·v2.

Used in the following modules: Energy

Knight, Thomas Andrew   (1759–1838) An English horticulturalist and botanist. He conducted extensive breeding experiments with strawberries, cabbages, peas, and various kinds of fruit, with the goal of improving food plants by selectively breeding for better qualities. He also studied inheritance in peas and came to many of the same conclusions as Gregor Mendel, but did not formulate a theory to explain his observations. Knight served as president of the London Horticultural Society from 1811 to 1838. He is remembered for his devotion to improving the quality of food plants, and inspired generations of horticulturists to bend their efforts in that direction.

Used in the following modules: Genetics II

Lamarck, Jean Baptiste   French zoologist and botanist, born in Bazentine le Petit (1744-1829). While working as a professor of invertebrate natural history at the Musée National d'Histoire Naturelle, Lamarck developed his theory of evolution, which stated that organisms could change in response to changes in their environment and could pass these changes on to their offspring, a theory later proven largely incorrect. For further information see Jean Baptiste Lamarck.

Used in the following modules: Adaptation

Used in the following modules: Scientific Institutions and Societies

Laplace, Pierre-Simon   French mathematician and astronomer born in Normandy, France (1749-1827). Laplace made significant contributions in mathematics and error quantification and is credited with founding the field of mathematical astronomy. In addition, he predicted the existence of black holes and the concept of gravitational collapse. For more information, see Pierre-Simon Laplace.

Used in the following modules: Data: Uncertainty, Error, and Confidence

Lattice   A characteristic pattern formed by the spatial distribution of repeating units.

Used in the following modules: Water

Lavoisier, Antoine   French chemist, born in Paris (1743-1794). He is famous for proving that air is composed of several gases - he thought 2. He also experimentally established the Law of Conservation of Mass, devised the system of chemical nomenclature that is currently in use, and authored the first modern chemistry textbook, Traité Élémenaire de Chimie (Elementary Treatise of Chemistry). For further information see Antoine Lavoisier.

Used in the following modules: Matter

Lawes, John Bennet   English gentleman farmer, born at the Rothamsted Manor House in Hertfordshire (1814-1900). He investigated the effects of various fertilizers on crops. Rothamsted Station is still now the oldest functioning agricultural research station in the world, and some experiments (termed Rothamstead Classical Experiments) have been running since it was founded. For further information, see John Bennet Lawes.

Used in the following modules: Data: Statistics

Le Verrier, Urbain   French astronomer, born in Saint-Lô, (1811-1877). He worked primarily on celestial mechanics and, like John Couch Adams, predicted the existence of Neptune based on perturbations in the orbit of Uranus. He also—incorrectly—predicted the existence of a planet inside the orbit of Mercury, which he named Vulcan, based on perturbations in Mercury’s orbit. For further information, see Urbain Le Verrier.

Used in the following modules: Gravity

Leaching   Dissolving out by the action of a percolating liquid.

Leclerc, Georges   French mathematician, naturalist and biologist, born in Montbard, Côte-d’Or (1707-1788). In 1727, Leclerc discovered the binomial theorem. In the 1730’s, he published Mémoire sur le jeu de franc-carreau (Thesis on the game of franc-carreau), which combined differential and integral calculus with probability theory. His most famous works are in natural history, where his ideas influenced the thinking of Lamarck and Darwin. His great work, Histoire naturelle, générale et particulière (General and specific natural history) consists of 36 volumes, published in 1749-1778, plus 8 more volumes published after his death. For more information, see Adaptation

Lehmann, Inge   Danish physicist born in Osterbro by the Lakes (1888-1993). In 1925, Lehmann became interested in seismology while working as assistant to Professor N.E. Norlund. Three years later, she was appointed chief of the seismological department at the Royal Geodetic Institute. Because Denmark is seismically stable, Lehmann focused her research on small earthquakes and explosions and the microseismic wave motions generated by Arctic and North Sea storms. From refractions of seismic waves, she discovered the Earth’s inner core 1936. In 1971, Lehmann was awarded the Bowie Medal by the American Geophysical Union for her contributions to the fields of seismology and earth science. For more information, see Inge Lehmann.

Used in the following modules: Earth Structure

Lenticular   Shaped like a lens, of or related to a lens; often referring to clouds, galaxies, rock bodies, or small features within rocks.

Used in the following modules: Research Methods: Description

Leukocytes   nearly colorless cells of the immune system that circulate mainly in the blood and lymph. Leukocytes participate in the immune system’s reactions to invading microorganisms or foreign particles.

Levene, Phoebus   (25 February 1869 – 6 September 1940) A Russian-American biochemist who studied the structure and function of nucleic acids, differentiated DNA and RNA (the two types of nucleic acid), and discovered that DNA consists of adenine, guanine, thymine, cytosine, deoxyribose, and a phosphate group. Levene is remembered for his “tetranucleotide hypothesis,” which he formulated around 1910, and which stated that DNA was composed of equal amounts of adenine, guanine, cytosine and thymine. Levene thought that DNA was too simple a molecule to carry genetic information, and favored the hypothesis that genetic material was stored instead in protein. Despite his misconceptions, his work contributed greatly to the eventual discovery of the importance of DNA.

Used in the following modules: DNA II

Lewis, Gilbert Newton   American chemist born in Weymouth, Massachusetts (1875-1946). Lewis’s early work, carried out as a faculty member at MIT, involved the determination of electrode potentials of elements, conductivity and thermodynamics. Most of his later work focused on thermodynamics and chemical equilibrium, electron-pair bonding of atoms and molecules, isotopes, and light-matter interactions. During his 34-year tenure at UC Berkeley, Lewis was renowned as a remarkable teacher and advisor. In 1923 he published Valence and the Structure of Atoms and Molecules, still considered a classic work and a vital contribution to modern bonding theory. For more information see Gilbert Newton Lewis.

Used in the following modules: Chemical Bonding

light   A form of electromagnetic radiation. Visible light is that associated with stimulating the organs of sight, which for normal human vision ranges in wavelength from 3900 to 7700 ångstroms.

limestone   A sedimentary rock composed mainly of calcite (CaCO3). Limestone forms through chemical precipitation in warm, shallow seas, and often contains marine fossils.

Used in the following modules: Plate Tectonics I, The Carbon Cycle

Limiting reactant   A reactant that limits the amount of product produced in a chemical reaction.

Line Spectra   An emission spectrum of light that contains very sharply defined lines. Line spectra are given off when matter is heated or excited in some way and each line corresponds to a wavelength of light given off during an electron transition from an excited state to the ground state.

Used in the following modules: Atomic Theory II, Data: Using Graphs and Visual Data

Lineage   in organisms, lineage is the line of descent from an ancestor.

Used in the following modules: Charles Darwin III

Linear   consisting of, or using, lines; in a line.

linnaean hierarchy   The seven major categories of biological classification based on Linnaeus’ system: Kingdom, Phylum, Class, Order, Family, Genus, and Species.

Linnaeus, Carolus   (also Carl Linnaeus or Karl von Linné) Swedish physician, naturalist and taxonomist born in Stenbrohult (1707-1778). Inspired by the work of John Ray, Linnaeus developed a system for classifying organisms, a modified version of which is still in use. In 1735, he published the first edition of Systema Naturae, which detailed his classification system. He was also the physician to the Royal Family of Sweden. For more information see Carolus Linnaeus.

Used in the following modules: Ideas in Science: Theories, Hypotheses, and Laws, Taxonomy I, Taxonomy II: Nomenclature

Lipids   A diverse group of organic molecules that contain long hydrocarbon chains or rings and are hydrophobic. Examples are fats, oils, waxes, and steroids.

Used in the following modules: DNA I, DNA III, Fats and Proteins

Lithosphere   The rigid upper layer of the earth consisting of the crust and the upper mantle. The earth’s tectonic plates are composed of pieces of the lithosphere. The lithosphere ranges in thickness from 10-12 km underneath the oceans to 70-200 km at the continents.

Used in the following modules: Earth Structure, Plate Tectonics II

Los Alamos National Laboratory   One of seventeen national laboratories overseen by the U.S. Department of Energy. LANL is located in Los Alamos, New Mexico, and was established in 1943 as a center for the design and development of the atomic bomb. Today, the focus of research at LANL is national security and nuclear deterrence. For more information, see the LANL website.

Used in the following modules: Scientific Institutions and Societies

Loschmidt, Johann Josef   Austrian chemist and physicist, born in Pocerny (now part of the Czech Republic) (1821-1895). He worked in thermodynamics, optics and electrodynamics. One of his many contributions to science was the accurate calculation of the average size of the gas molecules that make up air. For further information see Johann Josef Loschmidt.

Used in the following modules: The Mole

Lovelock, James   British chemist, born in Letchworth Garden City (1919-). He developed the Gaia Hypothesis, which proposes that the biosphere and all physical components of the Earth are coupled together in a complexly interacting system. The hypothesis is frequently paraphrased as describing the Earth as a single living organism. Lovelock was also an inventor: his most famous invention is the electron capture detector, which provided valuable information on the distribution of halogen-bearing chemicals and CFCs in the atmosphere. For further information see James Lovelock.

Used in the following modules: Research Methods: The Practice of Science

Lunar eclipse   A celestial event occurring when the Moon passes through some portion of the Earth's shadow. This only occurs when the Sun, Earth, and Moon are aligned so that the Earth is between the Sun and the Moon.

Used in the following modules: Research Methods: Description, Scientific Communication: Utilizing the Scientific Literature, The Nature of Scientific Knowledge

Lyell, Charles   A British geologist born in Scotland (1797-1875 CE). His most important work was The Principles of Geology: An Attempt to Explain the Former Changes of the Earth's Surface by Reference to Causes Now in Operation. Lyell championed the theory of uniformitarianism, which states that the same processes we see on earth today were active throughout the past and shaped the earth as we know it, including slow processes like sedimentation. This opposed the leading view at that time, catastrophism, which states that changes to the earth’s surface occur in sudden, discrete events. He also wrote Elements of Geology, which is still considered a seminal work on stratigraphy and paleontology. His third major, though now lesser known, work was The Antiquity of Man, in which he supports Darwin’s theories regarding the origins of species. The Lyell Medal is now awarded yearly by the Council of the Geological Society to a significant contemporary geologist. For further information see Charles Lyell; also see our module The Rock Cycle.

Used in the following modules: Charles Darwin II

MacLeod, Colin   (January 28, 1909 — February 11, 1972) A Canadian-American geneticist. He received his M.D. from McGill University in 1932, at the age of 23. Working with Oswald Avery and Maclyn McCarty, MacLeod showed that changes in the form or function of bacteria are caused by changes in DNA. The Avery-McCarty-MacLeod experiment was vital in the discovery that genetic material is contained in DNA, not in protein. Later in life, MacLeod became involved in health issues related to the Second World War, such as the microbial diseases typhus fever, malaria, and pneumonia, which posed serious threats to military personnel.

Used in the following modules: DNA I

Magellan, Ferdinand   (Portuguese: Fernão de Magalhães, c. 1480 – April 27, 1521) A Portuguese explorer who became a Spanish national so that he could search for a westward route to the Spice Islands (modern Indonesia) for King Charles of Spain. Magellan's expedition of 1519–1522 was the first to sail from the Atlantic Ocean to the Pacific Ocean, and the first to cross the Pacific. The expedition completed a circumnavigation of the globe, but Magellan was killed in battle in the Philippines. Magellan named the Pacific Ocean (from Latin, meaning the peaceful ocean), which he reached via what he named the Straits of Magellan. He also named the Magellanic penguin; he was the first European to describe it. He is remembered as one of the great explorers, and the Magellanic clouds, nearby dwarf galaxies visible from the southern hemisphere are named after him.

magma   Molten rock below the surface of the earth.

Used in the following modules: Ideas in Science: Scientific Controversy, Minerals I, Minerals II, Plate Tectonics I, Plate Tectonics II, Research Methods: Description, The Rock Cycle

Malthus, Thomas Robert   English ordained minister and economist born in Dorking, Surrey (1766-1834). In 1798 he published his Essay on Population, suggesting that a given population will always exceed its food supply, and it would therefore be counterproductive to provide starving populations with food. Instead, he argued, social equality must be achieved through other means, such as universal suffrage and state-funded education for the poor. For further information see Thomas Robert Malthus.

Used in the following modules: Charles Darwin II

Manhattan Project   A United States project initiated in August 1942 that was responsible for developing atomic technology, and specifically an atomic bomb, during World War II.

mantle   The middle portion of the interior of the earth, starting below the crust at 5-70 km below the earth’s surface and continuing to a depth of 2900 km. The mantle is composed mainly of the rock peridotite.

Used in the following modules: Earth Structure, Ideas in Science: Scientific Controversy, Minerals I, Minerals III, Plate Tectonics II

Mass   a fundamental property of matter which is a numerical measure of the inertia of an object or the amount of matter that an object contains. The mass of an object is different from its weight as mass is independent of the gravitational field exerted on an object.