The Cambrian explosion was caused by a lack of oxygen, not an abundance

Creatures from the black lagoon DURING the Cambrian period, which began 541m years ago, animal life took a remarkable leap forward. The first creatures believed by most (though not all) palaeontologists to be multicellular animals appear in the previous geological period, the Ediacaran. But though they are abundant and reasonably diverse, Ediacaran creatures do not look ancestral to modern animals. That is in contradistinction to Cambrian fossils, among which are found representatives of all the...