Help please,, it’s the second part to my previous question

Another factor can be photosynthesis.

Explanation:

During photosynthesis, plants would give off some oxygen as a waste product. The carbon dioxide would then move from the air into the leaves of the plants through tiny openings in the plant's leaves. Oxygen moves out of the plant's leaf through the same openings.

i think the miocene epoch spans the time from 23 million to 12 million years ago.