History of the Earth
Life in the Archean was limited to simple single-celled organisms (lacking nuclei), called prokaryotes. In addition to the domain Bacteria, microfossils of the domain Archaea have also been identified. There are no known eukaryote fossils.p306, 323 No fossil evidence yet exists for viruses. Fossilized microbes from terrestrial microbial mats show that life was already established on land 3.22 billion years ago.