12.1 Early Microbial Life on Earth 12.1.1 Conditions on Early Earth: hot and Anoxic 12.1.2 Evidence for Life on early Earth: Stromatolites 叠层石 12.2 Origin of Cellular life 12.3 Primitive Life: Early Metabolism 12.4 Eukaryotes and Organelles: Endosymbiosis 内共生