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Камбрий Камбрий (на латински: Cambrium) е първият геоложки период от палеозойската ера, чието начало е преди 542 ± 0.3 милиона години и край преди 488,3 ± 1,7 милиона години (МКС, 2004,[1] карта). Името на периода е дадено от Адам Седжвик от латинското име на Уелс (Cambria), т.е. мястото във Великобритания, където скалите от камбрий са най-достъпни. Периодът камбрий се характеризира с множество запазени фосили от тела на организми, както и техните черупки. Запазването на фосилни остатъци от меките тъкани позволява изучаването на финната структура на отдавна измрели видове, като това не е типично за някои от по-късните периоди, където подобни находки трудно се откриват. Камбрий маркира началото на глобална промяна на живота на Земята. Преди този период животът е с малки размери и значително по-примитивен, съставен предимно от едноклетъчни и колониални организми. Сложните многоклетъчни организми започват да се появяват малко преди и в ранните етапи на камбрий, като през периода достигат значителни размери и многообразие. Появата и разцвета на относително сложен живот се нарича „експлозия през камбрий“. Точно през този период на „експлозия“, се появяват представители на почти всички по-високи таксономични отдели. Докато животът е просперирал в океаните, земята е била почти необитаема с нищо повече от няколко микроорганизми. С изключение на няколко несигурни доказателства за животни излезли на сушата, повечето от континентите са били пусти и неприветливи. Моретата са сравнително топли, а полярния лед е почти стопен през този геоложки период. [редактиране] Източници - ↑ Gradstein, Felix M. и др. A Geologic Time Scale 2004. Cambridge, Cambridge University Press, 2004.
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Cambrian The Cambrian is the first geological period of the Paleozoic era. It lasted from 542 or 545 million years ago to 488 million years ago.[1] Before it came the Neoproterozoic, and after it the Ordovician. Biologists have learnt quite a lot about the soft parts of Cambrian animals. This is because places have been found where soft parts of organisms are preserved as well as their more resistant shells. This means our understanding of the Cambrian biota 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 the Proterozoic era. But during the Cambrian period, some organisms used carbonate minerals for shells, so they had hard parts which could become fossils. There were many different kinds of life during the Cambrian period. This diversification of lifeforms was relatively rapid, and is called the Cambrian explosion. This adaptive radiation produced the first members of the main groups of animals, called phyla. Almost all of this new life was in the oceans. There was little life on land except a layer of microbes. There were shallow seas near several continents, because a supercontinent called Pannotia had broken into smaller pieces. The seas were warm, and there was no ice at the North and South Pole. Many animals with hard shells appeared for the first time during the beginning of the Cambrian. [change] Change in the sea floor At the start of the Cambrian, the earlier animals (the Ediacaran biota) may have become extinct.[2] It seems these older life forms were affected by new types which burrowed into the sea floor.[3] This changed the conditions of life for the older types. The burrowing must have disturbed the mat of bacteria and algae which covered the sea-floor. About this time we find the first examples of many phyla. There are also some fossil traces on what was land at the time, so perhaps a few Cambrian organisms did leave the water. [change] Fossils Fossils from the Cambrian period sometimes show what the soft parts were like, unlike most fossils where the soft parts disappear. Fossils from the Burgess Shale in Ontario, 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: - First Cnidaria, and probable annelids, about 580 million years ago, in the Ediacaran period. - Small shelly fossils (SSF), including first molluscs and brachiopods, about 537 million years ago.[5] - First trilobites, about 526 million years ago. - First echinoderms, about 522 million years ago. - First crustaceans, about 510 million years ago. 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. [change] References - ↑ International Commission on Stratigraphy. - ↑ They may have continued in places where the sea-floor had not been so disturbed: see Fezouata Formation. - ↑ Butterfield N.J. 2001. The Ecology of the Cambrian radiation. Columbia University Press, New York. - ↑ Cowen R. 2002. History of life. Blackwell, Oxford. - ↑ Bengtson, S. (2004). Early skeletal fossils. In Lipps, J.H., and Waggoner, B.M.. "Neoproterozoic--Cambrian biological revolutions" (PDF). Palentological Society Papers 10: 67–78. http://www.cosmonova.org/download/18.4e32c81078a8d9249800021554/Bengtson2004ESF.pdf.