Surviving the Late Heavy Bombardment:
We find that the “last universal common ancestor” – a hypothetical very early single cell from which all life on Earth descended – existed prior to the “late heavy bombardment”. This was a period of intense meteor bombardment sustained by our planet about 3.9 billion years ago. This is significantly earlier than the currently accepted oldest fossil evidence would suggest (estimating 3.5-3.8 billion years ago).
The oldest confirmed fossils are from about 3.4 billion years ago, while the oldest potential fossils have been found on Greenland and date back to about 3.8 billion years ago. There’s also a suggestion that carbon found in a 4.1 billion-year-old mineral called zircon could be biological in nature. However, scientists have so far been unable to confirm that.
Some researchers think it would have been impossible for life to survive the late heavy bombardment, so that our oldest ancestor must be from after this phase. There are claims that the event would have sterilised the plants and vaporised any water around at the time. However, there are some recent mathematical models which suggest that pockets suitable for life could have remained.Holly Betts, “Ancestor of all life on Earth evolved earlier than we thought, according to our new timescale” at The Conversation
Earth is thought to be about 4.5 billion years old. That’s less time than ever for complex cellular dynamics to just sort of swish into place one day … but maybe the researchers who don’t discuss the problem are implicitly conceding that the chance scenario isn’t possible anyway. They can hardly do any harm by making the impossible less likely. 😉
See also: Earlier than thought: Worm burrows at rock layers over 600 million years ago
Researchers suggest: Life began on land not sea. And nearly 600 mya earlier than thought
Oldest known multicellulars are Ediacaran seaweed 555 mya
Stasis: Life goes on but evolution does not happen
Researchers’ proposed timescale,