An international team of researchers has unveiled new insights into Earth’s earliest ecosystem and came to a stunning result: life might have begun flourishing within a few hundred million years of the planet’s formation.
The study, published Friday in the journal Nature Ecology & Evolution, focuses on our Last Universal Common Ancestor (LUCA), the hypothetical common ancestor from which all modern cellular life descends.
This includes single-celled organisms such as bacteria all the way up through trees, shellfish, dinosaurs, and humans. LUCA is considered the root of the tree of life before it branches into Bacteria, Archaea, and Eukarya.
The team compared genes across the genomes of living species, tracking mutations that occurred since they shared an ancestor in LUCA. By aligning these genetic timelines with fossil records, they determined that LUCA existed around 4.2 billion years ago, approximately 400 million years after Earth’s formation.
“We did not expect LUCA to be so old,” Dr. Sandra Álvarez-Carretero, from the University of Bristol’s School of Earth Sciences, said in a statement. “However, our results fit with modern views on the habitability of early Earth.”
Further, the team modeled LUCA’s biology by examining the physiological characteristics of modern species and tracing them back to LUCA. “The evolutionary history of genes is complicated by their exchange between lineages,” explains lead author Dr. Edmund Moody. “We have to use complex evolutionary models to reconcile the evolutionary history of genes with the genealogy of species.”
Tracing it all back to LUCA
What’s remarkable about this study is how the genetic fingerprints of LUCA still exist in this wide diversity of species which would, on its surface, look irreconcilable.
“One of the real advantages here is applying the gene-tree species-tree reconciliation approach to such a diverse dataset representing the primary domains of life Archaea and Bacteria,” said study co-author Dr. Tom Williams from Bristol’s School of Biological Sciences. “This allows us to say with some confidence and assess that level of confidence on how LUCA lived.”
The study revealed that LUCA was a complex organism, similar to modern prokaryotes, and had an early immune system, indicating an ancient battle with viruses. “It’s clear LUCA was exploiting and changing its environment,” Co-author Tim Lenton, from the University of Exeter, said. “It is unlikely to have lived alone; its waste would have been food for other microbes, creating a recycling ecosystem.”
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