Scientists Find Evidence That Life May Have Originated Twice
An international research team published findings in Science Advances suggesting life on Earth may have emerged from two independent transitions to free-living cells around four billion years ago.
An international research team led by Natalia Mrnjavac and senior author William Martin has published findings in Science Advances suggesting that life on Earth may not have emerged from a single founding event, but rather twice around four billion years ago. The study proposes that bacteria and archaea independently made the transition from environment-dependent chemistry to free-living cells, pointing to parallel evolutionary pathways rather than one lineage branching into the other. Free-living cells likely emerged independently twice, with early metabolism relying heavily on inorganic catalysts in hydrothermal vent systems long before fully autonomous organisms took over energy processing.
To map the chemical timeline, the team analyzed the complete metabolic network of roughly 420 core reactions shared across all known life. Their reconstruction revealed that the last universal common ancestor, LUCA, possessed enzymes for only about half of these essential processes. The remaining reactions were not enzymatic at all; they were catalyzed directly by naturally occurring metals present in the hydrothermal vent environments where early chemistry took place. This metabolic split confirms that bacteria and archaea did not evolve from one another but independently arose from a primordial, non-living predecessor that remained chemically tethered to its surroundings.
The most striking evidence for two separate origins lies in how the two domains eventually bypassed their environmental dependencies. Bacteria and archaea both required solutions for those missing half of the core metabolic reactions, but instead of inheriting a shared toolkit from a single ancestor, they independently evolved structurally distinct enzymes to perform the same tasks. Those parallel inventions function as molecular fossils, preserving the record of two different chemical populations crossing the threshold into biological autonomy at roughly the same epoch.
Alongside the dual-transition model, the researchers identified a previously uncharacterized early energy mechanism rooted in those same vent environments. Phosphite reacting with organic compounds in the presence of palladium can catalyze metabolic phosphorylation without relying on ATP. That discovery provides a concrete chemical pathway for how prebiotic systems could have harvested and stored energy before sophisticated biological currency evolved, further clarifying the gap between abiotic chemistry and cellular function.
The work reframes a foundational question in biology by treating the earliest metabolic network not as a finished prototype but as an open system gradually closing around itself. The origin of life did not rely on a single event, but rather a widening chemical threshold that environment-driven reactions slowly gave way to enzymatic control, setting the stage for the independent trajectories that still define every domain of life today. The findings do not replace broader investigations into early biology; they simply show that the boundary between chemistry and biological autonomy may have been wider and more repeated than previous models allowed.