History of Earth's Atmosphere II: The Rise of Atmospheric Oxygen

What chemical is the source of the oxygen produced in photosynthesis?

• a.Air
• b.Carbon dioxide
• c.Water
• d.Iron oxide

When William Schopf first discovered microfossils, he was able to show that ______ is/are older than 600 million years.

• a.land plants
• b.photosynthetic microorganisms
• c.oxygen gas
• d.banded iron formations

Banded Iron Formations (BIFs) provide evidence that the early Earth lacked oxygen because

• a.they cannot form in the presence of abundant oxygen gas.
• b.they formed as sedimentary rocks in the oceans.
• c.they formed continuously for 1 billion years.
• d.they cannot form without the help of biological organisms.

In addition to Banded Iron Formations (BIFs), which line of evidence helped establish the timing of the Great Oxidation Event?

• a.Life on Earth arose between 3.8 and 3.5 billion years ago.
• b.Land plants evolved about 450 million years ago.
• c.Mars lost its atmosphere more than 4 billion years ago.
• d.Iron-rich “redbeds” began forming on land 2 billion years ago.

Uraninite forms a solid in the presence of oxygen.

• a.true
• b.false

The definition of mass independent fractionation (MIF) is when a reaction occurs and the abundances of different isotopes

• a.follow an expected pattern with more light isotopes and fewer heavy isotopes.
• b.follow an expected pattern with relatively more heavy isotopes than expected.
• c.do not follow an expected pattern. Rather, the pattern cannot be predicted from their mass.
• d.are equal.

Given a sulfur sample with the following relative abundances of sulfur isotopes (shown as δ^3XS), which of the following is NOT an example of mass independent fractionation?

• a.δ³⁴S > δ³³S > δ³²S > δ³⁶S
• b.δ³⁶S > δ³³S > δ³⁴S >δ³²S
• c.δ³²S> δ³³S> δ³⁴S> δ³⁶S
• d.δ³²S > δ³⁶S > δ³³S > δ³⁴S