Before life evolved on Earth, the atmosphere
A) had much higher concentrations of oxygen.
B) had much lower concentrations of carbon dioxide.
C) was more or less the same as it is now.
D) had much lower concentrations of oxygen.
E) had much lower concentrations of hydrogen.

Question

Quizplus · Accepted Answer

Before life evolved on Earth, the atmosphere had much lower concentrations of oxygen than it does now. Oxygen first started accumulating in the atmosphere due to photosynthetic organisms, which appeared later in Earth's history.

Before Life Evolved on Earth, the Atmosphere