A team funded by Nasa has discovered that some of Earth’s earliest life forms depended on the rare metal molybdenum more than 3 billion years ago, a finding that could reshape scientists’ understanding of how life evolved on the young planet.
The study, published in the journal Nature Communications, is the first to show that molybdenum played a biological role this early in Earth’s history, long before oxygen became abundant in the atmosphere.
Molybdenum is a trace metal that today sits at the core of enzymes responsible for major biological reactions involving carbon, nitrogen and sulphur.
These reactions are essential for sustaining life and maintaining planetary cycles such as the nitrogen cycle.
“Molybdenum sits at the catalytic center of enzymes that run major carbon, nitrogen, and sulphur reactions,” said Betul Kacar, senior author of the study and head of the Kaar Lab at the University of Wisconsin–Madison. “Asking when life began using molybdenum is really asking when some of the most consequential metabolic strategies became possible.”
The discovery surprised researchers because ancient Earth had extremely low amounts of molybdenum in its oceans.
Scientists had long suspected that early organisms may have first relied on another metal, tungsten, which behaves similarly in cells and is still used by some microbes living in extreme environments today.
Instead, the new study suggests that ancient microbes were already using both molybdenum and tungsten between 3.7 billion and 3.1 billion years ago, during the Eoarchean and Mesoarchean eras.
That places the use of molybdenum well before the Great Oxidation Event about 2.45 billion years ago, when photosynthetic microbes dramatically increased oxygen levels on Earth.
To reach the conclusion, researchers reconstructed the evolutionary history of metal-using enzymes across the tree of life and compared it with geological records of ancient ocean chemistry.
The findings suggest that even though molybdenum was scarce globally, early life may have obtained it from localised environments such as deep-sea hydrothermal vents, where metals accumulated in usable concentrations.
“Even if Archean seawater held little dissolved molybdenum overall, localised systems such as hydrothermal vents could still have supplied usable amounts,” Kacar explained.
Scientists say the study could have implications far beyond Earth. Understanding how ancient organisms adapted to limited resources may help astrobiologists rethink the search for alien life on planets with vastly different chemical environments.
“Our Nasa ICAR shows that mapping the evolutionary history of bio-essential elements on Earth can help us predict what life on other worlds might use,” Kacar said. “Life detection should be metal-aware, redox-aware, and evolution-aware.”
