What caused the Cambrian explosion of life?

[The Last Conformist]

so do we have evidence of these previous forms?

Well, sorta. We've got fossils of a decent number of advanced animals that predate the Cambrian explosion, but nothing to suggest earlier faunas were as diverse as Cambrian ones*. Saying that "all those different organisms had existed before the Cambrian explosion" is just plain wrong.

* It may be noted, in turn, that Cambrian faunas, even at their most exuberant, were much less diverse than modern ones.

 

[Archbob]

How advanced where the 'advanced' pre-cambrian animals. I was under the impression that clams, jellys, and the like all appears around 550 million years ago.

I think Coral might have been there in the end of the snowball earth days just before the cambrian age.

 

[AL_DA_GREAT]

The conditions were right at last