History of life on Earth: Cambrian explosion

Cambrian explosion

A relatively short period during which the early forms of the major groups of animals appeared suddenly in the fossil record.

When did the Cambrian explosion occur?

It occurred approximately 543 million years ago, during the Cambrian period.

Duration of the Cambrian period

Approximately 38 million years, from 543 to 505 million years ago.

Why is it called the Cambrian explosion?

Because there was a sudden appearance and rapid increase in the diversity of major animal groups in the fossil record.

Early animal groups of the Cambrian explosion

Platyhelminthes, Nematoda, Annelida, Mollusca, Arthropoda, Echinodermata and Chordata.

Platyhelminthes

Flatworms.

Nematoda

Worms.

Annelida

Segmented worms.

Mollusca

Animals such as slugs, snails and creatures with shells.

Arthropoda

Invertebrates with an external skeleton and jointed limbs.

Echinodermata

Marine invertebrates.

Chordata

Animals with a skeleton, including vertebrates.

Order of appearance of major animal groups in the booklet

Fish → amphibians → reptiles → birds → mammals → humans.

Approximate appearance of fish

438 million years ago.

Approximate appearance of amphibians

380 million years ago.

Approximate appearance of reptiles

225 million years ago.

Approximate appearance of birds

180 million years ago.

Approximate appearance of mammals

150 million years ago.

Approximate appearance of modern humans

250 000–300 000 years ago.