The Cambrian explosion
Animals diversify into most of the body plans we know
Quick facts
- Cambrian Period
- About 539 to 485 million years ago
- The explosion
- Rapid, in roughly the first 20 million years
- What appeared
- Most major animal body plans; nearly 40 phyla
- Signature animal
- Trilobites
What happened
The Cambrian Period, which the Natural History Museum dates from about 539 to 485 million years ago, opened with a burst of animal evolution so rapid and far-reaching that it is called the Cambrian explosion. In a geologically short window, thought to be only the first 20 million years or so of the period, animals diversified into full-bodied creatures with a wide range of body plans and lifestyles. Those body plans define what scientists call phyla, the major groups all animals are sorted into, of which there are nearly 40. Trilobites, hard-shelled arthropods with jointed legs and antennae, are the characteristic animals of the period.
Why it matters
Almost every kind of animal alive today, including the group that eventually led to us, traces its basic body plan back to this window. The change was so pronounced that the roughly four billion years of Earth history before it are often lumped together simply as the Precambrian, a single word for everything that came earlier.
How we know
The Natural History Museum in London dates the Cambrian to 539 to 485 million years ago, describes the rapid diversification into nearly 40 animal phyla, and identifies trilobites as the characteristic arthropods of the period.
Sources
- Natural History Museum, London. The Cambrian Period: how animals exploded onto the scene (Natural History Museum) (2024) · Reputable sourcenhm.ac.uk · The domain "nhm.ac.uk" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
- The Cambrian explosion (Current Biology, 2015, via PubMed) (2015) · Peer-reviewed (author-declared)pubmed.ncbi.nlm.nih.gov · Cited as a "journal" source (no stronger domain match). · Link is live and its text matches the event's key terms (Jul 2026)
See something wrong? . Corrections with a source get fixed fastest.
Part of a timelineBig Bang to Now19 events · 13.8 billion years on one timeline you can zoom, from the first light to the present. Every turning point cited.View all →