<P> Further evidence for early life is found in 3.47 - billon - year - old baryte, in the Warrawoona Group of Western Australia . This mineral shows sulfur fractionation of as much as 21.1%, which is evidence of sulfate - reducing bacteria that metabolize sulfur - 32 more readily than sulfur - 34 . </P> <P> Evidence of life in the Late Hadean is more controversial . In 2015, biogenic carbon has been detected in zircons dated to 4.1 billion years ago, but this evidence is preliminary and needs validation . </P> <P> Earth was very hostile to life before 4.2--4.3 Ga and the conclusion is that before the Archean Eon, life as we know it would have been challenged by these environmental conditions . While life could have arisen before the Archean, the conditions necessary to sustain life could not have occurred until the Archean Eon . </P> <P> Life in the Archean was limited to simple single - celled organisms (lacking nuclei), called Prokaryota . In addition to the domain Bacteria, microfossils of the domain Archaea have also been identified . There are no known eukaryotic fossils from the earliest Archean, though they might have evolved during the Archean without leaving any . No fossil evidence has been discovered for ultramicroscopic intracellular replicators such as viruses . </P>

Eighty percent of earth's continental area had formed by the end of the