A multinational study in Nature Ecology & Evolution estimates that the Last Universal Common Ancestor (LUCA) lived about 4.2 billion years ago, possibly only a few hundred million years after Earth formed. Researchers dated LUCA by comparing gene mutations across modern species and applying evolutionary separation models. Their reconstruction suggests LUCA was prokaryote-like but likely had primitive immune defenses and participated in early recycling ecosystems. The study highlights the need for more work to connect prebiotic chemistry with early microbial communities.
All Life From One Root: Study Suggests LUCA Existed Around 4.2 Billion Years Ago
Life’s Common Ancestor Lived 4.2 Billion Years Agoxxmmxx - Getty Images
Scientists trace every living thing on Earth back to a single ancestral organism called the Last Universal Common Ancestor (LUCA). A new multinational study, published in Nature Ecology & Evolution, pushes LUCA’s origin further back in time — to roughly 4.2 billion years ago — and reconstructs surprising features of that ancient life form.
Dating LUCA: How Researchers Worked Backwards
To estimate when LUCA lived, the team compared genes from a wide range of modern species and measured the mutations that accumulated since those lineages diverged. Using evolutionary models that account for genetic exchange between lineages and known separation times, the researchers infer that LUCA existed within a few hundred million years of Earth’s formation — placing it in the Hadean Eon when the planet was still geologically hostile.
“The common ancestry of all extant cellular life is evidenced by the universal genetic code, machinery for protein synthesis, shared chirality of the almost-universal set of 20 amino acids and use of ATP as a common energy currency. As such, our understanding of LUCA impacts our understanding of the early evolution of life on Earth. Was LUCA a simple or complex organism? What kind of environment did it inhabit and when?”
What LUCA May Have Been Like
Beyond timing, the team reconstructed likely physiological traits by tracing characteristics shared across living organisms back to their common ancestor. Their analysis suggests LUCA was prokaryote-like — relatively simple compared with modern multicellular life — but already equipped with systems that resemble primitive immune defenses, implying it was interacting with and defending against early viruses.
Co-author Tim Lenton (University of Exeter) notes that LUCA probably did not exist in isolation: its metabolic by-products would have supported other microbes, such as methanogens, forming recycling networks that shaped early ecosystems.
Why This Matters
Placing LUCA this early in Earth’s history changes how scientists think about the speed and conditions of life’s emergence. If life reached a common, cellular form so soon after planetary formation, the window for prebiotic chemistry and the transition to living systems may have been narrower and more efficient than previously believed.
Lead author Edmund Moody (University of Bristol) emphasizes the complexity of the analysis: evolutionary histories are tangled by gene exchanges across lineages, so the team used sophisticated models to reconcile gene trees with species trees and timing constraints.
Open Questions
LUCA is the deepest common ancestor researchers can infer from modern genomes, but it is not necessarily the very first living system. How chemistry gave rise to the first cells and how those early communities coalesced into the lineage that produced LUCA remain open questions. The authors call for further work combining geochemistry, paleontology, and molecular evolution to bridge the gap from prebiotic chemistry to early microbial ecosystems.
Bottom line: A new study supports an origin for LUCA around 4.2 billion years ago and suggests that even the earliest cellular life may have had defensive systems and ecological interactions — signaling a surprisingly dynamic early biosphere.
