Cambrian Period
When animal life exploded into the fossil record.
The Cambrian is the first period of the Paleozoic Era and the Phanerozoic Eon, spanning roughly 538.8 to 485.4 million years ago. It marks one of the most important moments in the history of life: the 'Cambrian Explosion,' a relatively rapid burst of diversification when most major groups of animals first appear in the fossil record.
GEOLOGIC POSITION
| Eon | Phanerozoic |
| Era | Paleozoic Era |
| Span | 538.8–485.4 Ma |
| Duration | ~53 million years |
| Preceded by | Ediacaran |
| Followed by | Ordovician |
AT A GLANCE
| Climate | Warm, with no permanent polar ice and high sea levels. |
| Geography | Most landmasses sat in the southern hemisphere as the supercontinent Gondwana assembled; the land itself was barren of complex life. |
| Key life | Almost entirely marine — the 'Cambrian Explosion' saw most major animal groups appear, including the first arthropods and the iconic trilobites. |
The world then
Earth looked alien. Continents were clustered largely in the southern hemisphere as Gondwana came together, and the land surface had no forests, soil, or animals — life was overwhelmingly in the sea. Sea levels were high and the climate was generally warm.
Life
Shallow seas filled with the first hard-shelled animals. Trilobites became abundant and are among the period's signature fossils, while large predators like Anomalocaris patrolled the water. Most modern animal body plans trace their origins to this window.
Why it matters
The Cambrian is where the animal fossil record truly begins — the deep root of everything that follows on the continental-drift timeline. Every later world, from the age of dinosaurs to the Ice Age, builds on this foundation.
Sources
Compiled by PaleoDex from open scientific data. Boundary ages follow the International Commission on Stratigraphy (ICS); descriptions draw on Wikipedia/Wikimedia. Where a fact isn't sourced, we leave it out rather than guess.
· Wikipedia · ICS International Chronostratigraphic Chart
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