Evidence of Archean life: Stromatolites and microfossils

Fossil evidence of the existence of life during the Archean Eon of Earth history (>2500 Ma) is summarized. Data are outlined for 48 Archean deposits reported to contain biogenic stromatolites and for 14 such units that contain a total of 40 morphotypes of described microfossils. Among the oldest of these putatively microfossiliferous units is a brecciated chert of the ∼3465 Ma Apex Basalt of Western Australia. The paleoenvironment, carbonaceous composition, mode of preservation, and morphology of the Apex microbe-like filaments, backed by new evidence of their cellular structure provided by two- and three-dimensional Raman imagery, support their biogenic interpretation. Such data, together with the presence of stromatolites, microfossils, and carbon isotopic evidence of biological activity in similarly aged deposits, indicate that the antiquity of life on Earth extends to at least ∼3500 Ma.