Transcript: The tree of life suggests that the first organisms on Earth were thermophiles, organisms that accustomed to and thrived in conditions of high temperature. The environments may have been hot springs or deep sea ocean vents. They came from two of the three branches of the tree of life, bacteria and archaea. They were prokaryotes or cells without nuclei. It’s possible that eukaryotic organisms also coexisted with the prokaryotes. They would not have left fossils, and we may not know when eukaryotes first evolved. The first organisms gained their energy from chemical reactions with hydrogen, sulfur, and iron compounds. These chemistry elements were abundant in the early Earth. They also evolved rapidly. The DNA had many copying errors. So there was rapid experimentation, and the natural selection operating on these different forms of chemistry would have proceeded very effectively.