History of the Earth
The earliest evidence for life on Earth is graphite of biogenic origin found in 3.7 billion–year-old metasedimentary rocks discovered in Western Greenland. Fossils of cyanobacterial mats (stromatolites) are found throughout the Archean—becoming especially common late in the eon—while a few other probable bacterial fossils are known from chert beds.p307 In addition to bacteria, microfossils of the extremophilic archaea have also been identified.