Hi.. its known for us that life originated on earth through a series of process for millions of years.. now if we go a bit brief into that, heard that bacteria called cyanobacteria produced oxygen billion of years ago, and from then on, species orignated on earth through the process of terraforming.. if that was true, did earth not have oxygen in its atmosphere before the origination of life.. can we discuss how life originated exactly on our planet, and about terraforming .. though we get some notes regarding these, but it will be easy to understand if wise people say..