How oxygen came into existence on earth

The planet’s atmosphere did not always contain oxygen.

One of science’s greatest mysteries is how and when oxygenic photosynthesis—the process responsible for producing oxygen on Earth through the splitting of water molecules—first began.

Now, a team led by geobiologists at the California Institute of Technology (Caltech) has found evidence of a precursor photosystem involving manganese that predates cyanobacteria, the first group of organisms to release oxygen into the environment via photosynthesis.

The findings strongly support the idea that manganese oxidation—which, despite the name, is a chemical reaction that does not have to involve oxygen—provided an evolutionary stepping-stone for the development of water-oxidizing photosynthesis in cyanobacteria

“Water-oxidizing or water-splitting photosynthesis was invented by cyanobacteria approximately 2.4 billion years ago and then borrowed by other groups of organisms thereafter,” Woodward Fischer, assistant professor of geobiology at Caltech and a coauthor of the study, said.

“Algae borrowed this photosynthetic system from cyanobacteria, and plants are just a group of algae that took photosynthesis on land, so we think with this finding we’re looking at the inception of the molecular machinery that would give rise to oxygen,” Fischer said

The research is published in the journal Proceedings of the National Academy of Sciences (PNAS).