Cyanobacteria was the bacteria that mass produced oxygen and filled the earth with oxygen. Where did this DNA come from considering that all previous life was poisonous to oxygen?
Before there was O2 requiring life, there were microbes that used other molecules such as sulphur. We really don't know how life originally evolved on this planet. Our best guess, is that this was a gradual process with more complex systems being more successful than simpler ones leading to the evolution of cellular life.
Answered By: Dr. Thomas Merritt