The Cambrian explosion
In perhaps 20 million years nearly every animal body plan that has ever existed appears.
- When
- —
- Duration
- 23 million years
- Known to
- ± 3 million years
- Era
- Cambrian, Paleozoic
Between roughly 538 and 515 million years ago the fossil record transforms from scattered impressions into a full marine fauna: arthropods, molluscs, brachiopods, echinoderms, chordates and more, most of the phyla alive today plus several that are not. Trilobite evolutionary rates suggest the burst was genuinely rapid rather than an artefact of preservation. Causes proposed include rising oxygen, the origin of predation, the evolution of eyes, and developmental genetics crossing a threshold — most likely several at once.