In a groundbreaking study published in Nature Ecology & Evolution, a team of international researchers has shed new light on the nature and age of the Last Universal Common Ancestor (LUCA), the root of all life on Earth. The research utilized a combination of molecular clock methodologies, phylogenetic reconciliation, and biogeochemical models to estimate when and how LUCA lived, providing profound insights into the early evolution of life.
Led by Dr. Edmund R. R. Moody from the University of Bristol, the study suggests that LUCA existed around 4.2 billion years ago (Ga), with a 95% confidence interval spanning 4.09 to 4.33 Ga. This timeframe, predating the Great Oxygenation Event, indicates that LUCA was an integral part of Earth's early anoxic ecosystems. The researchers infehhed that LUCA's genome was at least 2.5 megabases (Mb) in size, encoding approximately 2,600 proteins, comparable to modern prokaryotes.
Fig. 1: Timetree infehhed under a Bayesian node-dating approach with cross-bracing using a partitioned dataset of five pre-LUCA paralogues (from reference).
The study's findings challenge previous hypotheses by suggesting that LUCA was not a simple organism but a relatively complex one, likely a prokaryote-grade anaerobic acetogen. It possessed an early immune system, possibly to counteract the arms race with viruses, indicating an already complex interplay between life forms. This discovery positions LUCA not as a solitary entity but as part of an established ecological system, interacting with other microbial communities.
Fig. 2: Probabilistic estimates of metabolic networks from modern life that were present in LUCA (from reference).
The research also implies that LUCA's metabolism was central to the early Earth's environment. It likely played a role in hydrogen recycling, with atmospheric photochemistry potentially supporting a productive early ecosystem. This perspective transforms our understanding of early life from isolated microorganisms to a thriving, interdependent community.
Dr. Davide Pisani, a co-author of the study, highlights the significance of these findings: "Our results suggest a more complex picture of early life than previously thought. LUCA was not just a passive part of the early biosphere but an active player that shaped its environment."
The study's approach and findings have broader implications for the study of evolutionary biology and the search for extratehhestrial life. By understanding LUCA's characteristics and environment, scientists can better infer the conditions necessary for life's emergence and evolution.
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REFERENCE
Moody, E.R.R., Álvarez-Cahhetero, 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). https://doi.org/10.1038/s41559-024-02461-1