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content:life_sciences:life_itself:life_on_earth

Wikenigma - an Encyclopedia of Unknowns Wikenigma - an Encyclopedia of the Unknown

Life on Earth (timespan)

There is currently no scientific agreement as to how long ago life on Earth evolved. Estimates, based on geological evidence, vary by about 200 million years - from between 3.85 billion years ago (Ga), and 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

Further reading : Michael Marshall's detailed timeline as published in New Scientist (updated Apr. 2023)


Also see: Primordial Soupplugin-autotooltip__plain plugin-autotooltip_bigPrimordial Soup

"In 1953 an iconic set of experiments showed that some of the chemical building blocks of life, such as amino acids, could form spontaneously in the atmospheric conditions thought to prevail on the primordial Earth. This gave rise to the idea that the early oceans were a "primordial soup" from which life somehow emerged.
and Defining Lifeplugin-autotooltip__plain plugin-autotooltip_bigDefining Life

There isn’t, as yet, any definition of a 'lifeform' which can withstand logical scrutiny.

Exceptions can easily be found for any definition so far presented. For example (from The American Heritage Dictionary of the English Language

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