[SunkenCiv]

And here all this time I've been told that photosynthesis was the cause of the oxygen.

On a cellular basis, plants are more complicated than animals, so one possibility that has presented itself (from the materialist/reductionist perspective) is that unicellular animals appeared first, and then plants came along sometime later. That was difficult for the just-so school, who figured that plants woudl have to arise first. Extremophile bacteria of some sort are the leading candidates for the first Earthly life, but having a nice healthy catastrophe come along means having something to saddle on right away, y'know, for people who think that everything must have some connection with gradualism. :')

[ValerieUSA]

yes, what could be more sensible than gradualism?

[muawiyah]

I think the term "gradualism" is usually called "uniformitarianism" so they can rope in geologic change as well.

Of course uniformitarianism is totally wrong.