For decades, scientists believed that the atmosphere of early Earth was highly reduced, meaning that oxygen was greatly limited. Such oxygen-poor conditions would have resulted in an atmosphere filled with noxious methane, carbon monoxide, hydrogen sulfide, and ammonia. As the Earth cooled down, most of the water vapour condensed and formed the oceans.
To date, there remain widely held theories and studies of how life on Earth may have been built out of this deadly atmosphere cocktail.
