The Mesoarchean atmosphere contained high levels of atmospheric methane and carbon dioxide, which could be an explanation for the high temperatures during this era.
Like the gas giants (Jupiter and Saturn), Neptune’s atmosphere is composed primarily of hydrogen and helium, along with traces of hydrocarbons and possibly nitrogen, but contains a higher proportion of ices such as water, ammonia and methane.
Earth in the early Hadean had a very thick carbon dioxide- and methane-rich prebiotic atmosphere, but eventually oceans made of liquid water were formed.