AP BIOLOGY

Detailed explanation-1: -Oxygen was absent in early earth atmosphere.

Detailed explanation-2: -"Oxygen” was absent in the atmosphere in free form at the time of origin of life. Was this answer helpful?

Detailed explanation-3: -The oxygen did not build up in the atmosphere for a long time, since it was absorbed by rocks that could be easily oxidized (rusted). To this day, most of the oxygen produced over time is locked up in the ancient “banded rock” and “red bed” rock formations found in ancient sedimentary rock.

Detailed explanation-4: -What’s missing? The early atmosphere had almost no oxygen. Gases from Earth’s interior came through volcanoes and into the atmosphere.

Detailed explanation-5: -Scientists broadly agree that Earth’s early atmosphere and oceans were all but devoid of oxygen gas. But there are signs that there was some oxygen around. Geochemists, for example, have found mineral deposits dated to about 3 billion years ago that they argue could only have formed in the presence of oxygen.