The last common ancestor of all living organisms, from microscopic bacteria to giant sequoias, including humans, already inhabited the Earth 4.2 billion years ago: affectionately called Luca, ‘Last Universal Common Ancestor’, it was probably similar to current bacteria and already had an immune system to defend itself from attacks by the first viruses. This is stated in the study published in the journal Nature Ecology & Evolution and led by the British University of Bristol, which demonstrates how life flourished just 400 million years after the birth of our planet and the Solar System.
Researchers led by Edmund Moody compared all the genes present in the DNA of living species, counting the mutations that have accumulated over time since the last shared ancestor. Using a ‘genetic’ equivalent of the equation used to calculate speed in physics, they were able to go back to 4.2 billion years ago, the age of Luca: “We did not expect Luca to be so old – comments Sandra Álvarez-Carretero, co-author of the study – but our results fit with the modern vision of the habitability of the early Earth”.
The researchers then used the data obtained to shed light on the characteristics of this ancestor: the results indicate that it was a complex organism similar to current prokaryotes, unicellular microorganisms that include bacteria, and that it was not alone.
“It’s clear that Luke was already exploiting and modifying the environment he lived in, but it’s unlikely he was alone,” says Tim Lenton of the University of Exeter, one of the study’s authors. “His waste would have been food for other microbes, such as methanogens (bacteria that use hydrogen as an energy source and only live in the absence of oxygen), which would have helped create an ecosystem.”