Earliest Ancestors of Life Explored in Latest Scientific Study

An international team of scientists headed by the University of Bristol has provided insight into the earliest ecosystem on Earth, demonstrating that life was already thriving there a few hundred million years after the formation of the planet.

There is only one common ancestor, affectionately referred to as LUCA (Last Universal Common Ancestor), from whom all living things descended.

All contemporary cellular life, from single-celled creatures like bacteria to redwood trees (including us humans), is thought to have descended from LUCA, the postulated common ancestor. Before the Tree of Life was divided into the modern-day groups known as Bacteria, Archaea, and Eukarya, LUCA represented it.

Cellular organisms use amino acids to make proteins, the energy unit known as ATP, and cellular machinery like the ribosome and others involved in the synthesis of proteins from DNA information. The fact that all cellular life uses DNA to store information is one of the factors that led to the evolution of modern life from LUCA.

The scientists counted the mutations that have happened in the sequences of living species over time since they shared an ancestor in LUCA, and they compared every gene in each genome.

The scientists used a genetic equivalent of the well-known equation used to calculate speed in physics to determine when LUCA existed. The answer was 4.2 billion years ago, or roughly 400 million years after the formation of Earth and the solar system. The time of separation of some species is known from the fossil record.

We did not expect LUCA to be so old, within just hundreds of millions of years of Earth formation. However, our results fit with modern views on the habitability of early Earth.”

Dr. Sandra Álvarez-Carretero, Study Co-Author, School of Earth Sciences, University of Bristol

Next, the team worked out the biology of LUCA by modeling the physiological characteristics of living species back through the genealogy of life to LUCA.

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.”

Dr. Edmund Moody, Study Lead Author, University of Bristol

Co-author Dr. Tom Williams from Bristol’s School of Biological Sciences said: “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. This allows us to say with some confidence and assess that level of confidence on how LUCA lived.”

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.”

Davide Pisani, Study Co-Author and Professor, University of Bristol

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 findings and methods employed in this work will also inform future studies that look in more detail into the subsequent evolution of prokaryotes in light of Earth history, including the lesser studied Archaea with their methanogenic representatives,” added Anja Spang, Study Co-Author and Professor, Royal Netherlands Institute for Sea Research.

Co-author Professor Philip Donoghue said: “Our work draws together data and methods from multiple disciplines, revealing insights into early Earth and life that could not be achieved by any one discipline alone. It also demonstrates just how quickly an ecosystem was established on early Earth. This suggests that life may be flourishing on Earth-like biospheres elsewhere in the universe.”