2012: Advent Atmosphere: Algae

by on December 6, 2012

In the primordial soup era, when life first got started on Earth, it was anaerobic life. It worked without needing oxygen. It had to, because there wasn’t any oxygen around. At this point, the Earth still had a reducing atmosphere.

Right now, we have an oxidising atmoshere. If you leave iron sitting around where the air can get to it, it’ll rust – it’ll be oxidised by the atmosphere. Reduction reactions are sort of the opposite of that. That’s an oversimplification, but it’ll do for now. The long-ago atmosphere had almost no oxygen in it, tended to strip oxygen out of things it was in contact with, and reacted with things in ways sort-of-opposite to how it does now.

Life got its start in that kind of atmosphere, probably looking a bit like the things you find now around deep-sea vents, getting their energy from the minerals in the water. So when a species of algae hit on a clever trick for using energy from the sun instead, that was bad new for everything else. Photosynthesis produces oxygen as a waste product. If you’re photosynthesising, you don’t want oxygen. It’s no use for that reaction. So you dump it into the surrounding air, just to get rid of it.

It didn’t happen overnight. It took time. Some things managed to adapt. But plenty of things didn’t. The blue-green algae spread and thrived and vented toxic oxygen into the air, and as the poison built up, the Earth had its first mass extinction.

Leave a Reply