Cambrian explosion and Timeline of evolution
I'm willing to help with these articles - post a message on my Talk page if you're interested. I'd better warn you that I have a strong tendency to re-phrase existing content, as to many articles on science-related subjects suffer from logorrhoea, which I attribute to "academics envy"© (guess the derivation of this phrase!). I strongly believe that the target audience for Wikipedia is non-specialists and the target level of Fog index should be under 12. You may want to know a bit about my activities as an editor, so: I wrote most of the content in Physiology of dinosaurs (now re-arranged by others, discussions on-going), most of Permian-Triassic extinction, a lot of Cretaceous extinction and of Archosaur, and all of Evolution of mammals; and I've extensively edited  Extinction event.