Researchers at MIT have found evidence that some early life forms began using oxygen hundreds of millions of years before it accumulated in Earth's atmosphere. The study traces a key oxygen-processing enzyme to the Mesoarchean era, suggesting microbes consumed oxygen produced by cyanobacteria. This discovery challenges previous understandings of aerobic respiration's timeline.
Oxygen became a stable part of Earth's atmosphere around 2.3 billion years ago during the Great Oxidation Event, enabling the evolution of oxygen-breathing organisms. However, cyanobacteria, the first known oxygen producers, emerged about 2.9 billion years ago, generating oxygen through photosynthesis for hundreds of millions of years prior.
A new study by MIT geobiologists addresses why oxygen levels remained low despite this production. Published in Palaeogeography, Palaeoclimatology, Palaeoecology, the research examined heme copper oxygen reductases, enzymes essential for aerobic respiration that convert oxygen into water. These enzymes are present in most modern oxygen-breathing organisms, from bacteria to humans.
The team analyzed genetic sequences from thousands of species, mapping them onto an evolutionary tree of life and using fossil evidence to date branches. Their analysis indicates the enzyme first evolved during the Mesoarchean, from 3.2 to 2.8 billion years ago—several hundred million years before the Great Oxidation Event.
This timeline suggests that microbes near cyanobacteria quickly consumed the oxygen as it formed, preventing its atmospheric buildup. "This does dramatically change the story of aerobic respiration," said co-author Fatima Husain, a postdoc in MIT's Department of Earth, Atmospheric and Planetary Sciences. "Our study adds to this very recently emerging story that life may have used oxygen much earlier than previously thought."
Co-authors include Gregory Fournier of MIT, and Haitao Shang and Stilianos Louca of the University of Oregon. The findings build on prior MIT research confirming cyanobacteria's early oxygen production around 2.9 billion years ago. Husain noted, "We know that the microorganisms that produce oxygen were around well before the Great Oxidation Event."
The research highlights life's adaptability in Earth's early history, with organisms evolving to use oxygen in localized environments long before global oxygenation.