What Are the Signs of Oxygenation?

Risino bacteria do not like a lot of oxygen, so they produce a bunch of oxygen. Some cases, iron around in the water to grab that oxygen and then sink back down to the ocean floor and form a band. But sometimes a sign of bacteria would produce too much oxygen, it couldn't all get breathed in by this iron. And then they would poison themselves and lik kill themselves off. That leaves an imprint unde rock, basically like if there was a lot of oxygen or not - rocks look different.