The Cambrian Explosion: Definition & Timeline

Instructor: Jeff Fennell

Jeff has a master's in engineering and has taught Earth science both domestically and internationally.

The Cambrian Explosion refers to the metaphorical explosion of life that began 542 million years ago and lasted for roughly 40 million years. This lesson will cover the events that occurred during this time period.


For most of Earth's history, evolution has been a slow progression. The Cambrian Explosion, however, was a rapid evolution period starting 542 million years ago. Life expanded from simple, single-celled organisms to every current phylum of life known today over the course of roughly 40 million years. In terms of the geological time scale, this is unprecedented.

Artist rendition of Cambrian life forms
cambrian explosion

Some of the best evidence for the Cambrian Explosion comes from the Burgess Shale Formation in Canada. Discovered in 1909 by Charles Walcott, the shale formation is dated at 505 million years ago. While fossils are hard to preserve in general, this area is invaluable because fossils of organisms with soft bodies have been preserved in the rock bed.

Fossil trace from the Cambrian Explosion

There is some controversy in the scientific community about the Cambrian Explosion. Some scientists believe that life evolved rather gradually before 542 million years ago and that the fossil evidence has just been destroyed by time. Even Charles Darwin believed that the sudden appearance of many animal groups with no known ancestors went against his theory of evolution.

Precambrian (pre-542 million years ago)

Prior to the Cambrian Explosion, fossil records indicate a harsh world void of diverse life. Life on Earth consisted primarily of cyanobacteria, a simple single-celled bacteria that had been abundant in the ocean for over a billion years. For this period of a billion years, it is believed that cyanobacteria had not evolved much beyond forming a nucleus.

Explosion of Life (542 million years ago)

At 542 million years ago, the fossil record shows a rapid change in the abundance and diversity of life in the ocean. Most major animal groups appear for the first time in the fossil record as the Cambrian Explosion began. Every biological phylum of life that exists today can trace its origins back to the Cambrian Explosion.

One of the earliest forms of life that appeared during the Cambrian Explosion was a collection of small shelly fauna that appears in fossil records across the globe. Later life forms that appeared during the Cambrian Explosion include Arthropoda, Brachiopoda and Echinodermata. It is estimated that there was as much diversity of life in the oceans 542 million years ago as there is today.

Examples of anthropada

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