Researchers at Heinrich Heine University Düsseldorf and collaborating institutions have published findings in Science Advances suggesting that life on Earth may have originated twice, with bacteria and archaea emerging as distinct lineages rather than from a single common ancestor.
The international team examined genomes, protein structures, and chemical reactions to investigate early stages of microbial evolution. They analyzed a complete metabolic network of 420 chemical reactions that primitive cells would have used to manufacture essential biological components such as amino acids, RNA bases, and vitamins from materials available on early Earth, including hydrogen gas, ammonia, and carbon dioxide. The researchers discovered that while these metabolic reactions are highly conserved across all life forms, the enzymes catalyzing them show significant differences between bacterial and archaeal lineages.
According to the findings, the last universal common ancestor possessed enzymes for only half of the metabolic reactions, while the other half were likely catalyzed by metals naturally present in hydrothermal vent environments. The research identified four stages in the evolution of biological catalysis, beginning with purely metal-driven reactions, progressing through a hybrid phase combining metals and enzymes, and culminating in the independent evolution of distinct enzymes within each lineage. Notably, bacteria and archaea appear to have independently developed different enzymes capable of performing identical metabolic tasks, which may have enabled each lineage to transition toward independent cellular life.
The team also investigated energy sources for early metabolism, identifying palladium and phosphite—both naturally occurring in hydrothermal vents—as potential replacements for the complex ATP energy system used by modern cells. This discovery provides a plausible mechanism for powering the earliest metabolic reactions before sophisticated biological energy systems evolved.
According to the researchers, these findings indicate that bacterial and archaeal lineages achieved the free-living state independently, representing two separate origins of life despite sharing one genetic code origin.
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