Henry Gee

So the Cambrian period, as a period or what they call, geologists call a system of rocks,

started about then, but they keep changing their minds because it's very fluid.

It's a subject of major research, not just in paleontology, but in geology and geophysics, trying to work out what changed

in the system.

Before we had an idea of the absolute age, people wondered if there was a period before the Cambrian which was completely lost.

It had been completely eroded away to nothing in which all this evolution happened.

So that that being eroded away, you would then afterwards get the impression of nothing and then lots of things.

But it turns out that it's real.

there is a definite gap.

Oh, gosh.

Well, the Cambrian was, say, half a billion years ago.

The dinosaurs didn't appear until...

200 million years ago.

So that's just to emphasise just how much... At the earliest.

But of course, when the Cambrian had happened, like 8 9ths or 9 10ths of the Earth history had already happened.

And still the pre-Cambrian, we know very little about it.

I mean, we know a lot more than we did in Darwin's day, but there's still enormous gaps in our knowledge of what went on before the Cambrian.

I'll try and keep this a huge story brief.

About 2 billion years ago was an event called the Great Oxidation Event.

Well, it happened between 2.4 and 2 billion years ago, when for reasons nobody is quite sure, a lot of oxygen appeared in the atmosphere.