We don’t know all the evidence would be so tiny and so long ago we have no direct evidence. The most viable theory is that amino acids and proteins could have formed on the early Earth, in the primordial soup it was possible for these building blocks of life to form creating the primordial soup from which life could have spawned. https://youtu.be/Kq3Os00pPJM
What we do know is that an early from of live called Cyanobacteria formed Stromatolites and in the process turned a Carbon Dioxide rich atmosphere into one made from predominately Nitrogen and Oxygen. https://youtu.be/ile60Q3zsMU
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