Temperature: 45–70 °C
Atmospheric oxygen: 0%

Archean Eon – the second huge eon in the Earth history, which covers times from the formation of the first tectonic plates 4.0 billion years ago until the Great Oxidation Event 2.5 billion years ago.
At the beginning of this eon, Earth’s temperature was 2-3 times higher than the today. The causes of this phenomenon were: high concentration of greenhouse gases (tens of times higher than today) and heat from the formation and growth of the planet core.
At that time Sun had about 70–75% of the present luminosity. By the end of this eon, Earth’s tectonics were similar to the present, and there were vast oceans of liquid water.