The earliest period of the Paleozoic Era.
The Cambrian ran from 543 to 490 million years ago. During it, the fossil-producing
species of plants and animals
first proliferated – a dramatic diversification that has been called
the Cambrian Explosion. When the fossil record is looked
at closely, it turns out that the fastest growth in the number of major
new animal groups took place during the Tommotian and Atdabanian stages
of the Early Cambrian, a period of time which may have been as short as
five million years. In that time, the first undoubted fossil annelids,
onychophorans, poriferans, and priapulids show up in rocks all over the
The Cambrian, which was named by Adam Sedgewick after Cambria, the Roman
name for Wales, where rocks of this age were first studied, was preceded
by the Ediacaran Period and followed
by the Ordovician Period.
AND PLANETARY SCIENCE
AND EVOLUTION OF LIFE