"Molecular clock" study traces evolution back to ancestor of all life on Earth

[Judi Lynn]

Michael Irving
21 minutes ago

The further back in time you go, the patchier our understanding of life on Earth gets. That's because fossils from those early years are extremely hard to come by and interpret, for a number of reasons. Now, British scientists have used a different method known as a molecular clock to plot out a rough timeline of all life on Earth, tracing the first organisms back to about 4.5 billion years ago.

The fossil record is relatively rich back till around the Cambrian Period, when life exploded in diversity about 540 million years ago. Before then life was much simpler and didn't necessarily have the kinds of hard tissues that fossilize well, so the record largely rests on trace fossils – things like tracks and burrows that indicate the presence of life, rather than their bodily remains.

The fossil record gets murkier towards the Archaean period, over 2.5 billion years ago. The oldest confirmed fossils are about 3.4 billion years old, but other potential evidence includes a 3.5 billion-year-old hot spring in Australia, 3.7 billion-year-old stromatolites in Greenland, and the oldest (but most contentious) could be as ancient as 4.3 billion years.

"There are few fossils from the Archaean and they generally cannot be unambiguously assigned to the lineages we are familiar with, like the blue-green algae or the salt-loving archaebacteria that colors salt-marshes pink all around the world," says Holly Betts, lead author of the new study. "The problem with the early fossil record of life is that it is so limited and difficult to interpret – careful reanalysis of the some of the very oldest fossils has shown them to be crystals, not fossils at all."

More:
https://newatlas.com/ancestor-all-life-earlier/56003/