The last universal common ancestor is the hypothesized latest common ancestral population of single-celled organisms from which all subsequent life forms descend under the three-domain system of Bacte
Three ways to infer genes present in LUCA: universal presence, presence in both the Bacterial and Archaean domains, and presence in two phyla in both domains. The first yields as stated only about 30 genes; the second, some 11,000 with lateral gene transfer (LGT) very likely; the third, 355 genes probably in LUCA, since they were found in at least two phyla in both domains, making LGT an unlikely explanation.
Earliest known life forms
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The earliest known life forms on Earth may be as old as 4.1 billion years according to biologically fractionated graphite inside a single zircon grain in the Jack Hills range of Australia. The earlies
Last universal common ancestor
…as the diversity of extant viruses and their hosts—remains a subject of investigation. With no discovered fossil evidence of LUCA, it may precede the earliest known life forms. However, the detailed biochemical similarity of all current life makes its existence widely accepted by biologists. Its characteristics can be inferred…
Evidence of possibly the oldest forms of life on Earth has been found in hydrothermal vent precipitates.
Zircons in metaconglomerates from the Jack Hills in Australia show carbon isotopic evidence for early life.
Stromatolite fossil showing convex-up structures.
Archaea (prokaryotic microbes) were first found in extreme environments, such as hydrothermal vents.