Oxygen was once toxic pollution that poisoned most life
Bacteria dumping oxygen rusted the iron-rich oceans, and that rust still supplies our mines.
On Humans · How Do Humans Fit into the Story of Life? ~ Jonathan LohThe oxygen in the air was once toxic waste. Conservation biologist Jonathan Loh explains that tiny bacteria called cyanobacteria learned to use sunlight to split water apart, keeping the hydrogen to make food from carbon dioxide and dumping the oxygen.
That dump, known as the Great Oxidation Event, was a catastrophe. Oxygen is fiercely reactive, the same chemistry that turns iron to rust, and the ancient oceans were full of dissolved iron. The new oxygen rusted the seas, and the oxidized iron sank to the seafloor in striped layers called banded iron formations. Those deposits remain a major source of the iron ore mined today.
Most living things could not cope with the poison and retreated to oxygen-free refuges such as the deep ocean. Life rebounded after some organisms evolved to breathe oxygen, using it to unlock far more energy from food.
Questions people ask
When did the Great Oxidation Event happen?
Loh does not give a year date in the interview. He places it around June on his calendar that squeezes all of Earth history into one year. Outside the interview, geologists generally date the event to about 2.4 billion years ago, when oxygen began building up in air and seawater.
How did life learn to live with oxygen, let alone need it?
Some organisms evolved respiration, a chemical trick that uses oxygen to break down carbohydrates and release much more usable energy than oxygen-free metabolism. That energy powers complex life. Animals, including people, still depend on that ancient invention every time they breathe.
Do banded iron formations really supply iron today?
In Loh's account, the oxidized iron settled on the ocean bed as banded iron formations, and those rocks are a major source of the iron ore mined today. The interview does not name particular mines or say they are the single main source. That is as far as his claim goes.