Atmospheric levels of oxygen gas approached modern levels approximately ______ years ago.
A)5 billion
B)500 million
C)50 million
D)5 million
E)500 thousand

Question

Quizplus · Accepted Answer

Atmospheric levels of oxygen gas approached modern levels approximately 500 million years ago during the late Proterozoic and early Paleozoic eras, following the Great Oxidation Event and subsequent biological and geological processes.

Atmospheric Levels of Oxygen Gas Approached Modern Levels Approximately ______