Because there always needs to be something that starts it off. Eg: If there was no grass, there would be no animals.
I believe the answer is D, as we can reproduce and we have to be the same biological species to do that
Answer:
Cyanobacteria were photosynthetic and slowly changed the earth's atmosphere from CO2 rich to O2 rich. Photosynthetic cyanobacteria evolved by 3.5 billion years ago and greatly modified earth's atmosphere.
Atmosphere? I am not really sure what you are asking.
