http://www.shmoop.com/cell-respiration/evolution.html http://eesc.columbia.edu/courses/ees/climate/lectures/earth.html What were the first organisms on Earth and how did they get energy to live? What was the early Earth like and what gases were in the atmosphere? Where did the first oxygen come from? What organisms were responsible for the first oxygen on Earth? What organisms followed after Oxygen was available? How did eukaryotes form?