<Tr> <Td> Sea level (above present day) </Td> <Td> Rising steadily from 30m to 90m </Td> </Tr> <Tr> <Td_colspan="2"> Key events in the Cambrian view discuss edit - 550---- - 540---- - 530---- - 520---- - 510---- - 500---- - 490---- o p r o r o z o i l o z o i Ediacaran m r i n Ordovician r r n u i n r i s r i s u r o n g i n Fortunian "Stage 2" "Stage 3" "Stage 4" "Stage 5" Drumian Guzhangian Paibian Jiangshanian "Stage 10" * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Baykonurian glaciation Baykonurian glaciation * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * ← Orsten Fauna ← Burgess Shale ← Kaili biota ← Archaeocyatha extinction ← Emu Bay Shale ← Sirius Passet biota ← Chengjiang biota ← First Trilobites ← SSF diversification, first brachiopods & archaeocyatha ← First halkieriids, mollusсs, hyoliths SSF ← Treptichnus pedum trace Large negative peak δ 13C excursion ← First Cloudina & Namacalathus mineral tubular fossils Stratigraphic scale of the ICS subdivisions and Precambrian / Cambrian boundary . </Td> </Tr> <P> The Cambrian Period (/ ˈkæmbriən / or / ˈkeɪmbriən /) was the first geological period of the Paleozoic Era, of the Phanerozoic Eon . The Cambrian lasted 55.6 million years from the end of the preceding Ediacaran Period 541 million years ago (mya) to the beginning of the Ordovician Period 485.4 mya . Its subdivisions, and its base, are somewhat in flux . The period was established (as "Cambrian series") by Adam Sedgwick, who named it after Cambria, the Latinised form of Cymru, the Welsh name for Wales, where Britain's Cambrian rocks are best exposed . The Cambrian is unique in its unusually high proportion of lagerstätte sedimentary deposits, sites of exceptional preservation where "soft" parts of organisms are preserved as well as their more resistant shells . As a result, our understanding of the Cambrian biology surpasses that of some later periods . </P> <P> The Cambrian marked a profound change in life on Earth; prior to the Cambrian, the majority of living organisms on the whole were small, unicellular and simple; the Precambrian Charnia being exceptional . Complex, multicellular organisms gradually became more common in the millions of years immediately preceding the Cambrian, but it was not until this period that mineralized--hence readily fossilized--organisms became common . The rapid diversification of lifeforms in the Cambrian, known as the Cambrian explosion, produced the first representatives of all modern animal phyla . Phylogenetic analysis has supported the view that during the Cambrian radiation, metazoa (animals) evolved monophyletically from a single common ancestor: flagellated colonial protists similar to modern choanoflagellates . </P>

Where did the cambrian period get its name from