When did oxygen begin to accumulate in the atmosphere?
A)as soon as Earth was formed
B)about 2 billion years ago
C)about 200 million years ago
D)as soon as the early bombardment ended
E)as soon as life appeared

Question

Quizplus · Accepted Answer

Oxygen began to accumulate in the atmosphere approximately 2 billion years ago due to the process of photosynthesis by cyanobacteria. Before this, the atmosphere was mostly composed of nitrogen, carbon dioxide, and methane.

When Did Oxygen Begin to Accumulate in the Atmosphere