The Mesoarchaikum is a geological era. It is within the geological eon of the Archean, the third of four ages ( Mesoarchaikum = "middle Archean " ) dar. It starts before about 3,200 million years ago with the end of Paläoarchaikums and ends in front of about 2,800 million years ago with the beginning of Neoarchaikums. The stromatolites discoveries in Mkhonjwa Highlands northeast of Barberton in South Africa and the Steep Rock Lake, NW Ontario in Canada, where fossils of cyanobacteria were found to originate from the period before 3200 and before 2800 million years. The Pongolavereisung took place in front of about 2,900 million years ago.

See also: Geologic time scale