Define the cellmembrane and cell

Cellmembrane=the semipermeable membrane surrounding the cytoplasm of a cell.

Cell=the smallest structural and functional unit of an organism, typically microscopic and consisting of cytoplasm and a nucleus enclosed in a membrane. Microscopic organisms typically consist of a single cell, which is either eukaryotic or prokaryotic.

3.5 billion years ago, the earth atmosphere was dominated by carbon dioxide. The photosynthetic organisms took up the gas and used it in respiration. They produced oxygen as an end product which after being saturated in rocks became free air in the atmosphere. This event enabled aerobic life on earth.