For what reasons is it believed that oxygen was not present when life formed from earth

Explanation:

Why (for what reasons) is it believed that oxygen was not present when life formed on Earth? The life forms were anaerobic, and did not make oxygen. There is a lack of oxidized iron in rocks that are a few billion years old. Eventually oxygen from the oceans moved into the atmosphere, and iron could be oxidized.

is it believed that oxygen was not present when life formed on Earth? The life forms were anaerobic, and did not make oxygen. There is a lack of oxidized iron in rocks that are a few billion years old. Eventually oxygen from the oceans moved into the atmosphere, and iron could be oxidized.