Take two breaths. One came from the ocean.
More specifically, it came from microscopic plant-like organisms known at phytoplankton, which produce half of Earth’s oxygen as they drift around the ocean (and other water bodies). Together with land plants, these tiny, floating organisms help maintain the balance of gases that make up Earth’s modern atmosphere and make life as we know it possible.
But it wasn’t always this way. Earth’s atmosphere, which now contains roughly 21 percent oxygen gas, has gone through dramatic changes over the last 4.6 billion years. Earth’s first, or primordial, atmosphere was very similar to the composition of the sun–lots of hydrogen and noble gases, but no oxygen. Luckily for us, the pull of gravity and the chaos of rocky masses colliding in our early solar system stripped Earth of its primordial atmosphere.
Earth’s modern atmosphere, which is unique for its high concentration of oxygen, developed later. Understanding the story of the atmosphere, from the first draft to its modern form, has been a rich area of research for chemists, physicists, geologists and biologists. Although the picture has become clearer, there are still many unanswered questions about what caused oxygen level to rise quickly about 2 billion years ago during the “Great Oxidation Event” and what brought them up even further to modern concentrations about 600 million years ago.
We know some of the factors that contributed: the development of oceans as water precipitated, the rise of photosynthetic organisms (including phytoplankton’s early relatives), volcanic eruptions, and collisions by comets and other celestial bodies. But scientists are still working out how all these pieces fit together. And, even as our understanding of the past is coming into focus, researchers are tackling new questions about how human activities are shaping our atmosphere and Earth’s climate now and in the future.
For more about how scientists pieced together the mystery of Earth’s primordial atmosphere, visit our module The History of Earth’s Atmosphere I: The Origin of the Modern Atmosphere.
For a window into how Earth’s modern, life-supporting atmosphere developed, read our module The History of Earth’s Atmosphere II: The Rise of Atmospheric Oxygen.
For more about phytoplankton check out NASA Earth Observatory’s resource What are Phytoplankton?
Written by Christine Hoekenga
Christine is a freelance writer, editor, and content strategist, specializing in science and nature. She holds an Bachelor's degree in Environmental Science and Media Studies and a Master's of Science Writing. She has been working in science communication and education for nearly a decade as a journalist, an organizer for conservation groups, and a museum educator. Before joining the Visionlearning team, she served as the New Media and Online Community Manager for the Webby award-winning Smithsonian Ocean Portal. Christine is assisting Visionlearning with developing new modules and glossary terms, managing the blog, and outreach through social media.