[Udo]

> 200 million years before the first known multicellular fossils

This is a weird angle for the article to pursue. We have a monocellular fossil record that dates back 4.1 billion years, and I don't think anyone is proposing that we assumed up to this point oxygen levels took off because of multicellular life. A high oxygen level is probably one of many prerequisites for complex life, but that doesn't mean the genetic machinery was available as soon as it reached a certain concentration.

[omarchowdhury]

Wouldn't oxygen producing organisms such as plants and trees be a cause for oxygen levels taking off?

[adrianratnapala]

I thought even today phytoplankton produced more oxygen than all the multicellular plants put together.

I might just be imagining that factoid though.

[HCIdivision17]

That was my understanding as well. The idea being that there is a lot of volume in the first few meters of ocean surface area churn. It's not hard to imagine that does better in surface area than (even a lot) of plants.

[ethbro]

Not forgetting the fact that it seems like it would be substantially easier for a faintly mobile fluid filled bag(s) of DNA to survive and reproduce in an aqueous environment!

[dredmorbius]

You're getting ahead of yourself a bit. By a billion or two years.

The lifeforms that oxygenated the atmosphere were rather more primitive than trees. Generally cyanobacteria. Technically, yes, plants.

[ori_b]

Most oxygen (even today) is produced by single-celled algae in the ocean.

[Udo]

They're certainly sufficient but not necessary. There's no reason why single celled organisms couldn't do that. Maybe not at 20% but close.

[duaneb]

If my college biology understanding of evolution is at all accurate, a functional oxygen pathway would provide an edge in the ecosystem (read: high rates of population growth) and may have, in fact, been a catalyst for multi-cellular growth.

[ethbro]

The most recent discussion I heard seemed to be the theory that a functional oxygen pathway enabled multicellular life by providing enough surplus energy to power the entire organism in an evolutionarily efficient manner. (Add in the fact that by that point the planet was also teeming with single celled biomass to consume)