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.

Origin

Cambria is the Latin name for north Wales, a place of extensive Cambrian-age rocks investigated by Adam Sedgwick in the 1830s. Eventually as the stratigraphic series was filled out, the youngest 'Cambrian' came to overlap the oldest parts of the 'Silurian' sequence of strata that had been identified by Sir Roderick Murchison. In 1879, Charles Lapworth defined an 'Ordovician' period that included the overlapping beds.

Related Topics:
Latin - Wales - Adam Sedgwick - Stratigraphic series - Silurian - Strata - Roderick Murchison - Charles Lapworth - Ordovician

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