~539 million years agoReputable sourceWell documented
The Cambrian explosion
On the timeline · around ~539 million years ago · Geologic
What happened
Over a geologically short interval, most major animal body plans first appear in the fossil record.
Why it matters
The rapid diversification of complex animal life that underlies today's biosphere.
How we know
Exceptional fossil beds such as the Burgess Shale and Chengjiang; the Cambrian begins ~538.8 million years ago on the international time scale.
Sources
- Encyclopædia Britannica. Cambrian Period · Reputable source