An international team of researchers, led by the University of Bristol, has made a significant discovery regarding Earth’s earliest life forms. The study concludes that life began to flourish on our planet only a few hundred million years after its formation. This research focuses on LUCA, the Last Universal Common Ancestor, from which all modern cellular life—including bacteria, redwoods, and humans—originates.

LUCA is considered the root of the tree of life before it branches into the three major domains known today: Bacteria, Archaea, and Eukaryota. Modern life evolved from LUCA, utilizing common biochemical components such as amino acids for protein construction, the energy molecule ATP, cellular machinery like ribosomes for protein synthesis from DNA, and DNA itself for genetic information storage.

The research team compared the genes in the genomes of living species, counting the mutations that have occurred over time since these species shared an ancestor in LUCA. Using fossil records to determine the separation time of some species, the team applied a genetic equivalent of the equation used to calculate speed in physics to estimate when LUCA existed. Their findings suggest that LUCA lived approximately 4.2 billion years ago, just 400 million years after Earth and our solar system formed.

Dr. Sandra Álvarez-Carretero from Bristol’s School of Earth Sciences noted that the ancient age of LUCA was unexpected but aligns with modern views on the early habitability of Earth. The team modeled LUCA’s biology by tracing the physiological traits of living species back through their genealogy to LUCA. Lead author Dr. Edmund Moody explained that the evolutionary history of genes is complex due to their exchange between different lineages, necessitating sophisticated models to reconcile gene evolution with species genealogy.

One of the study’s key advantages, highlighted by a co-author from Bristol’s School of Biological Sciences, is the application of the gene-tree species-tree reconciliation approach to a diverse dataset representing the primary domains of life: Archaea and Bacteria. This methodology allowed the team to confidently assess how LUCA lived.

1990 phylogenetic tree linking all living beings with LUCA
1990 phylogenetic tree linking all living beings with LUCA. Credit: Chiswick Chap / Wikimedia Commons

Professor Davide Pisani, another co-author, noted that LUCA was a complex organism, not unlike modern prokaryotes. Interestingly, LUCA possessed an early immune system, indicating that even 4.2 billion years ago, our ancestor was engaged in a struggle against viruses. Co-author Tim Lenton from the University of Exeter’s School of Geography added that LUCA was likely part of a recycling ecosystem, with its waste serving as food for other microbes like methanogens.

The findings and methods of this study will inform future research on prokaryotic evolution, particularly focusing on the less-studied methanogenic Archaea, according to Professor Anja Spang from the Royal Netherlands Institute for Sea Research. Professor Philip Donoghue emphasized that the research combines data and methods from various fields, revealing insights into early Earth and life that couldn’t have been achieved by a single discipline. The rapid establishment of an ecosystem on early Earth suggests that life could potentially thrive in similar environments elsewhere in the universe.

The study involved scientists from University College London, Utrecht University, the Ecological Research Centre in Budapest, and the Okinawa Institute of Science and Technology Graduate University.

SOURCES

University of Bristol

Moody, E.R.R., Álvarez-Carretero, S., Mahendrarajah, T.A. et al. The nature of the last universal common ancestor and its impact on the early Earth system. Nat Ecol Evol (2024). doi.org/10.1038/s41559-024-02461-1

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