Scientists Discover Evidence of Two Origins of Life on Earth
A team of international researchers has found evidence that the first free-living cells may have emerged not once, but twice on Earth, suggesting that life may share one ancient genetic code but have undergone two separate transitions into free-living existence.
Life on Earth may have originated in two distinct forms, according to a groundbreaking study published in Science Advances. The research, led by biologists at Heinrich Heine University Düsseldorf, suggests that the first free-living cells may have emerged independently twice, with each lineage reaching the free-living state separately.
The study's findings are based on an examination of genomes, protein structures, and chemical reactions to investigate some of the earliest stages of microbial evolution. The researchers reconstructed the chemistry of early life, tracing the origins of enzymes during the earliest split between bacteria and archaea. They found evidence that free-living cells may have originated independently twice, with pioneer bacteria and pioneer archaea making their first attempts at life outside the confines of a hydrothermal vent.
The researchers identified four stages in the early evolution of biological catalysis, with reactions driven entirely by metals being followed by a stage in which metals and enzymes worked together. Within each lineage, newly evolved enzymes gradually replaced the inorganic catalysts supplied by the environment where metabolism had first developed.
One of the study's major advances was the reconstruction of the metabolic network known as metabolism, which contains 420 highly connected reactions. The researchers developed a method to arrange metabolic reactions from the simplest to the most complex, which may reflect the order in which those reactions appeared during the earliest stages of biological evolution.
The study's findings have significant implications for our understanding of the origins of life on Earth. According to the researchers, the broader implication of their findings is that bacteria and archaea did not make the transition to independent cellular life together. Instead, each lineage appears to have reached the free-living state separately.
The researchers also identified a new source of energy at metabolic origin, involving palladium, a metal that occurs naturally in hydrothermal vents. They found that phosphite, a form of phosphorus naturally found in hydrothermal vents, can react with organic compounds in the presence of palladium and produce reactions associated with metabolic phosphorylation.
The study's findings are the result of an international collaboration involving researchers from Heinrich Heine University Düsseldorf, the Universities of Canterbury, Rostock, Constance, Ottawa, Strasbourg, and Tübingen, the Max-Planck-Institute for Terrestrial Microbiology, the Max-Planck-Institut für Kohlenforschung, and the IMDEA Materials Institute.
## Reconstructing the Chemistry of Early Life
The researchers examined the complete group of chemical reactions that cells use to manufacture key biological components from materials that were available on the early Earth. They found that the enzymes responsible for carrying out those reactions do not show the same degree of conservation between bacteria and archaea.
## From Metal Catalysts to Enzymes
The study's findings suggest that early biochemical evolution was a hybrid of enzymatic and metal catalysts. The researchers identified examples in which bacteria and archaea appear to have independently developed different enzymes capable of performing the same essential metabolic task.
## How Early Metabolism May Have Been Powered
The researchers investigated what could have supplied energy before ATP-based metabolism existed. They found that phosphite, a form of phosphorus naturally found in hydrothermal vents, can react with organic compounds in the presence of palladium and produce reactions associated with metabolic phosphorylation.
## Mapping 420 Reactions at the Origin of Metabolism
The research is the first study specifically focused on the full reaction network known as metabolism. The researchers developed a method to arrange metabolic reactions from the simplest to the most complex, which may reflect the order in which those reactions appeared during the earliest stages of biological evolution.
## One Genetic Code, but Two Origins of Life
The study's findings have significant implications for our understanding of the origins of life on Earth. According to the researchers, the broader implication of their findings is that bacteria and archaea did not make the transition to independent cellular life together. Instead, each lineage appears to have reached the free-living state separately.
The researchers also suggest that the new data leave only one conclusion: the bacterial and archaeal lineages made the transition to the free-living state independently. Only free-living cells are alive, and the study's findings provide a possible explanation for how some of the earliest metabolic reactions could have obtained the energy needed to proceed before modern biological energy systems evolved.
The study's findings are a significant step forward in our understanding of the origins of life on Earth. The researchers' discovery of evidence for two origins of life on Earth challenges our current understanding of the origins of life and highlights the complexity and diversity of early life on Earth.
