Around 2.5 billion years ago, our planet experienced what was possibly the greatest change in its history: According to the geological record, molecular oxygen suddenly went from nonexistent to becoming freely available everywhere. Evidence for the “great oxygenation event” (GOE) is clearly visible, for example, in banded iron formations containing oxidized iron. The GOE, of course, is what allowed oxygen-using organisms — respirators — and ultimately ourselves, to evolve. But was it indeed a “great event” in the sense that the change was radical and sudden, or were the organisms alive at the time already using free oxygen, just at lower levels?
Prof. Dan Tawfik of the Weizmann Institute of Science’s Biomolecular Sciences Department explains that the dating of the GOE is indisputable, as is the fact that the molecular oxygen was produced by photosynthetic microorganisms. Chemically speaking, energy taken from light split water into protons (hydrogen ions) and oxygen. The electrons produced in this process were used to form
— source Weizmann Institute of Science | Mar 1, 2021