All life on Earth has a common origin and it may be even older than scientists thought.
The precise origin of life on Earth is an eternal question that comes back and becomes more precise over the centuries. For scientists, life on Earth comes from LUCA (Last Universal Common Ancestor), the first universal common ancestor of all living beings. For a long time, the appearance of LUCA was dated to around 4 billion years ago, or 600 million years after the formation of the planet. This estimate has been revised by a new study conducted by an international team of scientists and published in Nature Ecology & Evolution.
“The common ancestry of all extant cellular life is demonstrated by the universal genetic code, the mechanism of protein synthesis, the shared chirality of the nearly universal set of 20 amino acids, and the use of ATP as a common energy currency,” the study first details. ATP is an essential element of life for living organisms.
To find out when LUCA appeared on Earth, the experts compared the genes of living species and counted the mutations that occurred. They identified 2,600 protein-coding genes that could be traced back to LUCA. Using an equation based on the time of the species split, the experts concluded that LUCA was probably a little older than previous estimates had suggested.
He must have been on Earth 400 million years after the planet’s creation, or 4.2 billion years ago. Sandra Álvarez-Carretero, co-author of the study, said of these results: “We did not expect LUCA to be so old, a few hundred million years after the formation of the Earth. However, our results are consistent with modern conceptions of the habitability of the early Earth.”
What did this common ancestor look like? According to the study, LUCA was a prokaryote, an organism whose cell nucleus is mixed with the cytoplasm, probably equipped with an immune system and reproductive mechanisms. In addition, it did not live alone: ”It is clear that LUCA exploited and modified its environment, but it is unlikely that it lived alone. Its waste could have served as food for other microbes, such as methanogens, which would have helped create a recycling ecosystem,” explained Tim Lenton, co-author of the study. Gray areas remain as to how life then evolved from this common ancestor.