# The Cambrian explosion

- kind: problem
- status: open
- year: 1859

**Statement.** Why did most animal body plans appear within about 20 million years, around 540 million years ago?

Candidate causes include rising oxygen, predation arms races, and the evolution of developmental gene networks. Precambrian fossils have made the explosion look less sudden than it once did, but its trigger is still argued.

## Sources

- [Wikipedia: Cambrian explosion](https://en.wikipedia.org/wiki/Cambrian_explosion)

[Origins](/wiki/Space:origins-of-life.md) · [Life](/wiki/Continent:life.md)

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