An international team of researchers has published new insights into Earth’s oldest ecosystems, coming to a surprising conclusion: life may have begun to thrive within a few hundred million years of Earth’s formation.
The study was published in the journal Natural Ecology and Evolutionfocuses on the Last Universal Common Ancestor (LUCA), a hypothetical common ancestor from which all modern cellular life originated.
This includes everything from single-celled organisms such as bacteria to trees, shellfish, dinosaurs, and humans. LUCA is thought to be the root of the tree of life before it branched off into bacteria, archaea, and eukaryotes.
The team compared genes across the genomes of modern species to track mutations that have occurred since the birth of a common ancestor called LUCA. By matching these genetic timelines with the fossil record, they determined that LUCA existed roughly 400 million years after the formation of the Earth, about 4.2 billion years ago.
“We didn’t expect LUCA to be so old,” said Dr Sandra Alvarez-Carretero, from the University of Bristol’s School of Geosciences. statement“But our findings are consistent with modern views of the habitability of early Earth.”
What’s more, the team modelled LUCA’s biology by looking at physiological traits of modern species and tracing them back to LUCA. “The evolutionary history of genes is complicated by exchanges between lineages,” explains lead author Dr Edmund Moody. “Reconciling the evolutionary history of genes with species lineages requires the use of complex evolutionary models.”
Trace it all back to LUCA
What’s remarkable about this study is that genetic traces of LUCA still exist in a variety of seemingly incompatible species.
“One of the real advantages here is that we’ve applied the gene tree and species tree reconciliation approach to a very diverse dataset representing the major domains of life: archaea and bacteria,” said co-author Dr Tom Williams, from the School of Biological Sciences at the University of Bristol. “This allows us to make statements with some confidence about how LUCA may have lived, and to assess that level of confidence.”
The study reveals that LUCA was a complex organism similar to modern prokaryotes, with an early immune system, suggesting it may have been fighting ancient viruses. “It’s clear that LUCA was using and transforming its environment,” said co-author Tim Lenton of the University of Exeter. “It is unlikely that it lived alone, and its waste would have provided food for other microbes, creating a circular ecosystem.”
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