What is the process that doesn’t require oxygen

Photosynthesis!

Plants breath carbon dioxide and let's out oxygen.

(I don't really know, but I think it's photosynthesis)

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

an active site is a region that is present on an enzyme where the reactants or the substrate molecules we can say bind and experience a chemical reaction. the substrate is basically a reactant whose concentration is changing and that is converting into a product after binding at the active site of an enzyme