About 4 billion years ago, cyanobacteria started using photosynthesis to dramatically increase the amount of energy they could use. One byproduct of this was the release of unprecedented amounts of oxygen.
This was fine, for a while, because the earth had reserves of minerals that bonded with free oxygen and kept it out of the oceans and the atmosphere. But eventually (2.4 billion years ago) those oxygen sinks became saturated, and atmospheric oxygen began to rise.
Most early life at this point was anaerobic, and for those species, the new oxygen was a deadly toxin. Rising O2 levels wiped out nearly all life on earth. Even the cyanobacteria faced significant challenges as the oxygen converted methane in the atmosphere into CO2 and water, triggering a 200 million year ice age that remains the longest “snowball earth” period in history.
The more I learn about the Oxygen Catastrophe, the more obvious the parallels to anthropogenic climate change get. I can’t decide whether it’s reassuring that even when a single species threw the ecosystem that far out of whack, it wasn’t the end of everything, or depressing that after everything humans have learned and accomplished, we’re still making the same mistakes as single-cell organisms 2.4 billion years ago.
Also, I think it’s high time that the blue-green algae community started talking about reparations for surviving anaerobic populations.