Henry Gee

Well, when we call the Cambrian explosion an explosion, it's more of a kind of extended detonation.

It's more of a difficult title to sell if we call it the Cambrian extended detonation.

Yes, or the Cambrian slow, digestive rumble.

But in terms of geology, it was because that hiatus in the fossil record that so worried Darwin

is real.

I mean, there was a step change in evolution, partly motivated by the input of calcium minerals into the sea.

And the whole thing lasted about 50 million years, which is less than the time between the dinosaurs and now.

And that was a time in which almost, in fact, all modern phyla, that is large categories of animals, appeared in the Cambrian.

Except one, but even that's been cleared up now.

So what's that?

That's the Bryozoa, or moss animals.

These are tiny, tiny colonial creatures that live in little boxes and tentacles coming out.

And that was thought to be the kind of slacker that didn't appear in the Cambrian, but now...

Some fossils were found and some people said, yes, these are Bryozoa.

And somebody said, no, these aren't Bryozoa, they're seaweed.

And the first lot came up with some more and said, yes, they're Bryozoa.

So that's been settled, which is nice.

Yes, well, the difference between land and sea would be quite stark.

I mean, there have been some suggestions that some life was ashore in the Cambrian.

In fact, before the Cambrian, there are some deposits in northwest Scotland, which are a billion years old,