The age of microbes
Geochemical evidence, in the form of traces of organic carbon in rocks, suggests that life existed nearly 3.9 billion years ago. From 3.9 to about 1.2 billion years ago, life was confined to microbes, or single-celled organisms. During this time, the microbes prospered, gradually altering their surroundings. The conditions they created made the environment hospitable for the emergence of more complex life-forms, beginning about 1.2 billion years ago.
Keywords: Life (Biology), Life--Origin, Microorganisms, Micropaleontology