At the time of the First Great Oxidation Event, the oxygen concentration in Earth's atmosphere increased:
A) from 15 to 21 percent.
B) due to oxygen production by zooplankton.
C) from trace amounts to appreciable quantities.
D) due to accelerated weathering caused by lichens.

Question

Quizplus · Accepted Answer

The First Great Oxidation Event refers to a time (around 2.4 billion years ago) when the concentration of oxygen in Earth's atmosphere increased from trace quantities to appreciable quantities. This was due to the evolution of photosynthetic organisms (such as cyanobacteria) that produced oxygen as a waste product during photosynthesis. The oxygen reacted with iron in Earth's crust and ocean, leading to the deposition of banded iron formations.

At the Time of the First Great Oxidation Event, the Oxygen