Home > Cambrian Explosion
The Cambrian Explosion is the radiation of animal phyla that started about 570 million years ago, which is 30 million years after the beginning of the Cambrian geologic period, and lasted between 5 and 17 million years through much of the early Cambrian. The extinctions connected with the Varangian glaciation that preceded this radiation (popularized as ' Snowball Earth'), along with subsequent greenhouse warming of the Earth, is theorized to have provided the evolutionary impetus. It is thought that the development of sexual reproduction increased the rate of evolutionary change. Evidence for earlier multicellular animal forms, which may have been the precursors of this radiation, date from 600 million years ago. Notable among these are trace fossils in the form of imprints of animals and their activities, such as burrow s in mud, produced by animals that paleontologists call the Ediacaran faunaFauna is a collective term for animal life. The corresponding term for plants is flora. Technically, the proper term for fauna plus flora is biota but fauna is often used instead. In zoology and paleontology the term is often used to refer to the typical. These organismIn biology and ecology, an organism is a living being. The origin of life and the relationships between its major lineages are controversial. Two main grades may be distinguished, the prokaryotes and eukaryotes. The prokaryotes are generally considered tos were soft-bodied and are found with various strange body forms. The so-called Small shelly faunaThe small shelly fauna is the name given to an obscure collection of small hardshelled fossils found worldwide in beds a bit older than the earliest trilobites and archeocyathidsin Nemakit-daldiyan stage (lower Cambrian). The start of the Cambrian period of the ensuing Tommotian period included Cloudinia and its kin. All phyla in existence today (and all others now extinct) except one were first found in this period.
The original and most widely-publicized source of fossils from the actual radiation period is the Burgess ShaleThe Burgess shale (named after Mount Burgess, near where the shale was found) is a black shale found high up in the Canadian Rockies in Yoho National Park near the town of Field, British Columbia. Fossils were found in the Burgess Shale by C. Walcott in 1 in British ColumbiaBritish Columbia or simply B. French: la Colombie-Britannique is the westernmost of Canada's provinces. It was the sixth province to join the confederation of Canada (in 1871). As of 2004, the population was 4,168,123 British Columbians . Geography Its ca. Some Burgess Shale organisms display strikingly unusual body plans that are not easily connected with any phyla known since.
A popular account of the paleontological analysis of the Burgess Shale is given in Wonderful Life by Stephen Jay Gould.
The Cambrian Explosion has recently been a controversial topic regarding the history and evolution of life, with the idea posited that the Burgess Shale preserved such a wide variety of life and that the "Cambrian Explosion" was actually a slower radiation of animal forms than previously thought. The idea of an "explosion" of life in the Cambrian period is still being debated.
Paleontology Geologic timescale
