Atmosphere of Earth years ago. About 3.4 billion years ago, nitrogen formed the major part of the then stable "second atmosphere". The influence of life has to be taken into account rather soon in the history of the atmosphere, because hints of early life-forms appear as early as 3.5 billion years ago. How Earth at that time maintained a climate warm enough for liquid water and life, if the early Sun put out 30% lower solar radiance than today, is a puzzle known as the "faint young Sun paradox". The geological record however shows a continuous relatively warm surface during the complete early
Atmosphere of Venus to have had a Venus-like atmosphere, with roughly 100 bar of CO and a surface temperature of 230 °C, and possibly even sulfuric acid clouds, until about 4.0 billion years ago, by which time plate tectonics were in full force and together with the early water oceans, removed the CO and sulfur from the atmosphere. Early Venus would thus most likely have had water oceans like the Earth, but any plate tectonics would have ended when Venus lost its oceans. Its surface is estimated to be about 500 million years old, so it would not be expected to show evidence