Earliest known life forms

The earliest known life forms on Earth may be as old as 4.1 billion years (or Ga) according to biologically fractionated graphite inside a single zircon grain in the Jack Hills range of Australia. The earliest evidence of life found in a stratigraphic unit, not just a single mineral grain, is the 3.7 Ga metasedimentary rocks containing graphite from the Isua Supracrustal Belt in Greenland. The earliest, directly known life on Earth are stromatolite fossils which have been found in 3.480-billion-year-old geyserite uncovered in the Dresser Formation of the Pilbara Craton of Western Australia.

From Wikipedia, under CC BY-SA. More on occurri.