Cambrian

The Cambrian is a major division of the geologic timescale that begins about 542 million years before the present (BP) at the end of the Proterozoic eon and ended about 488.3 million years BP with the beginning of the Ordovician period (ICS, 2004). It is the first period of the Paleozoic era of the Phanerozoic eon. The Cambrian is the earliest period in whose rocks are found numerous large, distinctly-fossilizable multicellular organisms that are more complex than sponges or medusoids. During this time, roughly fifty separate major groups of organisms or "phyla" (a phylum defines the basic body plan of some group of modern or extinct animals) emerged suddenly, in most cases without evident precursors. This radiation of animal phyla is referred to as the Cambrian explosion.

Cambrian palaeogeography

Cambrian continents are thought to have resulted from the breakup of a neoproterozoic supercontinent called Rodinia. The waters of the Cambrian period appear to have been widespread and shallow. It is thought that Cambrian climates were significantly warmer than those of preceding times that experienced extensive ice ages discussed as the Varanger glaciation. Continental drift rates in the Cambrian may have been anomalously high. Because of their complexity, it is difficult to describe continental motions in text. Time-sequenced maps of paleo-continents and other major geologic features are called paleomaps and are available at several Internet sites (see below).

Related Topics:
Continent - Neoproterozoic - Supercontinent - Rodinia - Climate - Ice age - Varanger glaciation - Continental drift - Paleomap

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