The Cambrian Period is not divided into eras, but rather into epochs. These epochs are:

* Terreneuvian: 541 to 521 million years ago

* Second Series: 521 to 509 million years ago (currently unnamed, but sometimes informally referred to as the "Miaolingian")

* Furongian: 509 to 485.4 million years ago

These epochs are based on major changes in the fossil record, particularly the appearance and diversification of animal life.

It's important to note that the "Cambrian Explosion" - a period of rapid diversification of life - occurred primarily during the Terreneuvian and Second Series epochs.