Why don't textbooks discuss the "Cambrian explosion," in which all major animal groups appear together in the

Why don't textbooks discuss the "Cambrian explosion," in which all major animal groups appear together in the fossil record fully formed instead of branching from a common ancestor -- thus contradicting the evolutionary tree of life?

They do, sweetie. Try reading them. You might learn something. Such as that no theory suggests that all major animal groups branch from a common ancestor.

It's a bummer when you've been lied to, isn't it?

Probably because:

A) They do discuss the Cambrian explosion; you just haven't been paying attention,

B) While people like to make the Cambrian explosion sound like a sudden event, in reality it was an extended period of several million years,

C) There are animal fossils which pre-date the Cambrian explosion, so the idea all the major animal forms appeared very suddenly in the Cambrian is a load of horse$#!+,

D) Very few animals that even come close to resembling modern animals appeared in the Cambrian, and absolutely NO land animals appeared during that period, so the idea all the major animal forms appeared very suddenly in the Cambrian is a load of horse$#!+, and

E) We know both why fossils from before that period are exceptionally rare, and why so many different types of animals evolved during that time period... so there's no reason to point out the Cambrian explosion "contradicts the evolutionary tree of life" because it can be reasonably accounted for, and doesn't actually contradict the Theory of Evolution (but rather fits into it rather nicely).