A new study from researchers at the University of Wisconsin–Madison shows that 3.4 billion years ago, life on Earth relied on a metal called molybdenum, despite its limited availability at the time. Published in Nature Communications, the study is the first to trace molybdenum’s use this far back in time.

Molybdenum is a metal vital for many biochemical processes because it speeds up the rate of chemical reactions needed to perform those processes, such as nitrogen fixation. These reactions could still occur without the metal, but not fast enough to sustain life.

“What is kind of counterintuitive is that, according to the geochemical record, molybdenum abundance on the early Earth seems to have been a lot lower billions of years ago, particularly before the advent of oxygenic photosynthesis,” says Aya Klos, a PhD student in bacteriology at UW–Madison.

Yet for some reason, despite its limited availability, life continued to evolve using biochemical processes that rely on molybdenum. Those processes have been passed down to modern-day organisms.

For the study, the researchers also tracked molybdenum in cells to understand how it moves through and is used by them. The team plans to continue research aimed at understanding why life would continue to invest in molybdenum-reliant biochemical processes even when other, more plentiful elements were available.

They also traced back in time the use of tungsten, a metal that can act like molybdenum but is typically associated with modern organisms that live in extreme environments. The study suggests that life was already experimenting with both molybdenum and tungsten billions of years ago.

Betül Kaçar, a professor of bacteriology at UW–Madison and the senior author of the paper, explains that understanding which elements early life relied on can aid astrobiologists in identifying other planets that could potentially support life.

“This study shows that just because an element is scarce in the environment doesn’t mean life will not find a way to use it and even build an empire with it,” Kaçar says. “Life works in surprising ways. Discoveries like this remind us that the search for life beyond Earth may require us to imagine possibilities we haven’t yet considered.”