TheCambrian is the first geological period of thePalaeozoicera and thePhanerozoiceon. It lasted from 541 million years ago to 485.4 million years ago.[1] Before it came theEdiacaran, and after it theOrdovician.
Biologists have learnt quite a lot about the soft parts of Cambrian animals. This is becauseplaces have been found where soft parts of organisms are preserved as well as their more resistant shells. This means our understanding of the Cambrianbiota is better than that of some later periods.
Life on Earth changed greatly during the Cambrian period. Before the Cambrian, life was mostly small and simple. Complex organisms (metazoa)evolved during theProterozoic era. But during the Cambrian period, some organisms usedcarbonateminerals forshells, so they had hard parts which could become fossils. There were many different kinds of life during the Cambrian period. This increase in the diversity of lifeforms was relatively rapid, and is called theCambrian explosion. Thisadaptive radiation produced the first members of the main groups of animals, calledphyla.
Almost all of this new life was in the oceans. There was little life on land except a layer ofmicrobes. There were shallow seas near several continents, because asupercontinent calledPannotia had broken into smaller pieces. The seas were warm, and there was no ice at theNorth andSouth Pole. Many animals with hard shells appeared for the first time during the beginning of the Cambrian.
At the start of the Cambrian, the earlier animals (theEdiacaran biota) may have becomeextinct.[2] It seems these older life forms were affected by new types whichburrowed into the sea floor.[3] This changed the conditions of life for the older types. The burrowing must have disturbed the mat ofbacteria andalgae which covered the sea-floor. About this time we find the first examples of manyphyla. There are also some fossil traces on what was land at the time, so perhaps a few Cambrian organisms did leave the water.
This is how the sea floor changed during the Cambrian period.
Fossils from the Cambrian period sometimes show what the soft parts were like, unlike most fossils where the soft parts disappear. Fossils from theBurgess Shale inOntario,Canada are examples of fossils with soft parts.[4] Here are some life forms that first appeared in the Cambrian period, with the oldest ones first:
It is not always clear which phylum a fossil should be put into. So there are some fossils which are still being discussed, years after they were discovered.
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