As yet, there is no scientific agreement as to the age of life on Earth. Estimates (based on geological evidence) currently vary by about 200 million years. That's to say between 3.85 billion years ago (Ga), or 3.65 Ga.
To date, the oldest undisputed fossils appear in rocks from 3.2 Ga, but recent carbon dating techniques applied to rocks from Akilia Island, in Greenland, which checked the ratios of carbon isotopes, found suggestions of life at 3.85 Ga.
Further reading Astrobiology Magazine (NASA), 2006
Although the earliest reasonable estimates for the 'proven' age of life are around 3.7Ga, some research groups point to the possibility that it could have arrived considerably earlier, but left no measurable traces :
The habitability boundary could be as early as 4.5 Ga, the earliest possible estimate of the time at which Earth had a stable crust and hydrosphere, or as late as 3.9 Ga, the end of the period of heavy meteorite bombardment.
Source: arXiv:1808.09460, 2018
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