Study finds life on Earth may have arisen twice

The first free-living cells on Earth may not have emerged in a single event. Instead, bacteria and archaea — the two primordial lineages of life — appear to have independently crossed the threshold from non-living chemistry to living organisms, according to a study published Tuesday in Science Advances.eurekalert+1

An international team led by biologists at Heinrich Heine University Düsseldorf traced the deep history of metabolism, the network of roughly 420 chemical reactions cells use to build amino acids, RNA bases, and vitamins from simple compounds. Their analysis points to a shared chemical beginning at hydrothermal vents, followed by two separate routes toward cellular independence.

A Shared Ancestor With Incomplete Chemistry

The researchers reconstructed the metabolic capabilities of LUCA, the last universal common ancestor of all cells. They found that LUCA possessed enzymes for only about half of the reactions needed for metabolism. The remaining reactions were likely catalyzed by metals — iron, nickel, cobalt, and palladium — naturally present in hydrothermal vent systems.thebrighterside+1

The team identified four stages in the rise of catalysis: an initial phase relying entirely on metals, a metal-enzyme hybrid stage in LUCA, and then two divergent paths as bacteria and archaea each developed their own enzymes to replace environmental catalysts. In five cases, the two lineages evolved structurally unrelated proteins to carry out the same essential reaction — evidence of parallel, independent invention.sciencealert+2

"The new data leave only one conclusion," said senior author William Martin. "The bacteria and archaeal lineages made the transition to the free-living state independently. Only free-living cells are alive. Let's call it by name: we are looking at one origin of the genetic code, but two origins of life."eurekalert+1

An Energy Source Before ATP

The study also addresses how early metabolism was powered before ATP existed. The team demonstrated that phosphite, a reduced form of phosphorus found in serpentinizing hydrothermal environments, combined with palladium could drive phosphorylation reactions in water overnight — replacing the role of ATP and enzymes in transferring chemical energy.bioengineer+2

"Phosphite and palladium replace ATP and enzymes; it's amazing, and it makes early evolution a lot easier to grasp," said Manon Schlikker of the Düsseldorf team.sciencealert

Rewriting the Tree of Life

The findings reframe the origin of life as two events rather than one. While all cellular organisms share a single genetic code inherited from LUCA, the capacity to live independently from a mineral-rich vent environment may have been achieved separately by bacteria and archaea. Uncertainties remain — archaeal enzymes are less thoroughly characterized, and many proposed metal-driven reactions still lack direct experimental confirmation. But the study offers researchers a defined reaction network, a possible energy source, and a specific geological setting to test further.smithsonianmag+2