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
Ideas for new topics, and suggested additions / corrections for old ones, are always welcome.
If you have skills or interests in a particular field, and have suggestions for Wikenigma, get in touch !
Or, if you'd like to become a regular contributor . . . request a login password. Registered users can edit the entire content of the site, and also create new pages.
( The 'Notes for contributors' section in the main menu has further information and guidelines etc.)