From Ethan Siegel at Starts with a Bang:
By finding graphite deposits in zircons that are 4.1 billion years old, graphite deposits that show this carbon-12 enhancement, we now have evidence that life on Earth goes back at least 90% of Earth’s history, and possibly even longer! After all, finding the remnants of organic matter in a certain location means the organic matter is at least as old as the location it’s buried in, but it could still be even older. This is so early that it might make you think that perhaps this life didn’t originate here on Earth, but that Earth was born with life. And this could really, truly be the case.
(Extended argument follows, summation:)
If all life on Earth has a universal common ancestor, couldn’t it be that there are many forms of ultra-primitive life in the Universe, and the type that came to Earth that was best adapted to the early Earth’s environment was the type that thrived, evolved, reproduced, and out-competed all the others? We don’t have enough evidence to favor this hypothesis over any other, but if we continue to push this limit back earlier and earlier: 4.3 billion years, 4.4 billion years, 4.45 billion years… it’s going to be harder and harder to argue that this life didn’t come to Earth already alive in some sense. More.
See also: What we know and don’t know about the origin of life
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