What is a "reducing atmosphere"

In Biology, we were discussing the early environment at the beginning of time. My teacher mentioned the "reducing atmosphere" but I don't know what that is.

For the origin of life, it means there were reduced gasses, such as ammonia (NH3) and methane (CH4), in the atomsphere. So carbon, for example, existed in its most reduced form (CH4) not in an oxidized form (CO) or a fully oxidized form (CO2).

Miller's experiment modeled a highly reduced atmosphere, but a highly reduced atmosphere is now doubted for the prebiotic earth.

A reducing atmosphere, also known as a reduction atmosphere, is an atmospheric condition in which oxidation is prevented by removal of oxygen and other oxidising gases or vapours.


Kinda irrelevent to your lesson?...