An international team involving UCL researchers has shed light on Earth's earliest ecosystem, showing that within a few hundred million years of planetary formation, life on Earth was already flourishing.
Everything alive today derives from a single common ancestor known affectionately as LUCA (Last Universal Common Ancestor).
LUCA is the hypothesised common ancestor from which all modern cellular life, from single celled organisms like bacteria to the gigantic redwood trees (as well as us humans) descend. LUCA represents the root of the tree of life before it splits into the groups, recognised today, Bacteria, Archaea and Eukarya.
Modern life evolved from LUCA from various different sources: the same amino acids used to build proteins in all cellular organisms, the shared energy currency (ATP), the presence of cellular machinery like the ribosome and others associated with making proteins from the information stored in DNA, and even the fact that all cellular life uses DNA itself as a way of storing information.
The team, led by the University of Bristol and involving researchers at UCL Earth Sciences and UCL Division of Biosciences, compared all the genes in the genomes of living species, counting the mutations that have occurred within their sequences over time since they shared an ancestor in LUCA.
The time of separation of some species is known from the fossil record and so the team used a genetic equivalent of the familiar equation used to calculate speed in physics to work out when LUCA existed, arriving at the answer of 4.2 billion years ago, about four hundred million years after the formation of Earth and our solar system.
Co-author Professor Graham Shields (UCL Earth Sciences) said: "This fact that life's common ancestor lived so early on was quite a surprise and points to a much earlier origin for life itself. This contradicts a widely held notion among scientists that meteorite impacts rendered our planet sterile throughout the first half billion years of its existence."
Next, the team worked out the biology of LUCA by modelling the physiological characteristics of living species back through the genealogy of life to LUCA. Lead author Dr Edmund Moody, of the University of Bristol, explained: "The evolutionary history of genes is complicated by their exchange between lineages. We have to use complex evolutionary models to reconcile the evolutionary history of genes with the genealogy of species."
Co-author Professor Davide Pisani, of the University of Bristol, said: "Our study showed that LUCA was a complex organism, not too different from modern prokaryotes, but what is really interesting is that it's clear it possessed an early immune system, showing that even by 4.2 billion years ago, our ancestor was engaging in an arms race with viruses."
Co-author Tim Lenton (University of Exeter, School of Geography) said "It's clear that LUCA was exploiting and changing its environment, but it is unlikely to have lived alone. Its waste would have been food for other microbes, like methanogens, that would have helped to create a recycling ecosystem."
The study involved scientists from UCL, the universities of Bristol, Exeter and Utrecht, the Royal Netherlands Institute for Sea Research, the Centre for Ecological Research in Budapest, and Okinawa Institute of Science and Technology Graduate University.
The research was funded by the John Templeton Foundation. The opinions expressed in this publication are those of the author(s) and do not necessarily reflect the views of the John Templeton Foundation.
