BY:SpaceEyeNews.
A new study proposes that life on Earth began twice, but the idea needs careful explanation. The researchers do not claim that life emerged from nonliving chemistry in two unrelated events. Instead, they argue that the ancestors of bacteria and archaea independently became self-sufficient, free-living cells.
Both lineages share an ancient genetic foundation. Their paths separated while their metabolic systems still depended partly on hydrothermal chemistry. Each lineage then developed different enzymes to perform some of the same essential tasks.
The findings appeared in a peer-reviewed Science Advances study published on August 5, 2026.
What “Life on Earth Began Twice” Really Means
All known cellular life traces back to a population called LUCA, the last universal common ancestor. LUCA already possessed the genetic code and parts of the molecular machinery shared across life today.
However, the new research suggests LUCA was not fully independent in the modern sense. It may have depended on metals and chemical conditions within a hydrothermal environment. Those surroundings could have performed reactions that enzymes handle inside present-day cells.
The phrase “two origins of life” therefore refers to two later transitions. One occurred along the bacterial branch and another along the archaeal branch. It does not describe two separate beginnings from lifeless matter.
Reconstructing the First Metabolic Network
The international team examined 420 core metabolic reactions. These reactions allow cells to turn hydrogen, carbon dioxide, ammonia and other simple materials into amino acids, nucleotide components and cofactors.
Researchers compared genomes, enzyme structures and known chemical reactions across the network. They also used a mathematical method to arrange reactions from simpler to more complex stages.
The analysis produced a possible sequence for the rise of metabolism. It began with metal-driven chemistry. A hybrid phase followed, in which enzymes and environmental catalysts worked together. Bacterial and archaeal ancestors then followed different evolutionary paths.
The Heinrich Heine University research summary describes four proposed phases. These range from metal-only chemistry to separate enzyme systems in bacteria and archaea.
LUCA May Have Relied on Hydrothermal Metals
According to the study, LUCA possessed enzymes for only about half of the examined metabolic reactions. Metals in its environment may have catalyzed many of the remaining steps.
Hydrothermal systems provide useful ingredients. Water-rock reactions can produce hydrogen and expose metals such as iron, nickel and cobalt.
The researchers describe early biochemistry as a partnership between geology and biology. Primitive enzymes handled part of the work, while mineral catalysts supplied other functions.
Over time, cells developed biological replacements for those external catalysts. This shift would have reduced their dependence on a particular location. Metabolism could operate inside cells instead of remaining tied to reactive mineral surfaces.
Life on Earth may have begun twice.
Two Cellular Paths Reached Independence
One result gives the “life began twice” interpretation its strongest support. The team identified five cases in which bacteria and archaea use structurally unrelated enzymes to complete the same essential reaction.
If both lineages had inherited those enzymes directly from LUCA, the proteins should retain signs of a common structure. Instead, their differences suggest that each lineage found its own molecular solution after separating.
These parallel innovations may have completed the metabolic systems needed for independent life. Bacterial ancestors replaced environmental catalysts with one set of enzymes. Archaeal ancestors developed different proteins for equivalent jobs.
The finding does not erase their common ancestry. It shows how a shared genetic system may have supported two separate routes toward metabolic independence.
Energy Before the Modern ATP System
The study also addresses a major energy problem. Modern metabolism relies heavily on ATP, yet early chemistry could not depend on a complex molecule that cells must manufacture.
Researchers tested phosphite, a form of phosphorus associated with serpentinizing hydrothermal systems. In water, phosphite and native metals supported phosphorylation reactions without modern enzymes. Experiments using palladium even converted AMP into ADP under controlled conditions.
This result offers a plausible bridge between geological and biological energy management. However, it does not recreate a complete ancestral metabolism. It only demonstrates that specific reactions can occur under proposed early-Earth conditions.
Why the Findings Matter Beyond Earth
If life on Earth began twice in the limited sense proposed, metabolic independence may not require one uniquely improbable solution. Different lineages might use different catalysts and enzymes to cross the same threshold.
That possibility makes ocean worlds especially interesting. NASA’s Cassini findings support hydrothermal activity beneath the ice of Enceladus. The moon also contains a global ocean and chemicals relevant to habitability.
Europa probably has a salty ocean in contact with a rocky seafloor. NASA considers water-rock interactions a possible source of hydrogen, minerals and chemical energy there. Europa Clipper will investigate whether the moon offers conditions suitable for life.
Still, the study does not show that life exists on either moon. It also does not calculate the likelihood of extraterrestrial life. Instead, it offers a testable model for how environmental chemistry might gradually become cellular metabolism.
A Compelling Proposal, Not a Final Answer
Origin-of-life research reconstructs events that left no direct cellular record. This model depends on evolutionary comparisons, ancient-environment assumptions and laboratory simulations. Other pathways may also explain how early metabolism developed.
Even so, the research connects several difficult stages within one framework. Metals first supported chemical reactions. Enzymes gradually replaced them. Two ancient lineages then completed that transition through different molecular inventions.
Conclusion: Did Life on Earth Begin Twice?
The statement that life on Earth began twice is accurate only under the study’s specific definition. The genetic foundation appears shared, while bacteria and archaea may have independently reached a free-living state.
The study does not identify two unrelated creations of life. Instead, it suggests that chemistry became autonomous biology along two evolutionary routes. If future evidence supports the model, life’s earliest history may look less like one sudden beginning and more like a gradual process with multiple solutions.
Main Sources:
- Science Advances: Intermediate Stages in the Origin of Metabolism
- Heinrich Heine University: Two Origins of Life
- NASA: Enceladus Hydrothermal Activity
- NASA: Why Europa Has Ingredients for Life