User:Abyssal/Portal:Cambrian

Portal topics: Activities; Culture; Geography; Health; History; Mathematics; Nature; People; Philosophy; Religion; Society; Technology; Random portal

The Cambrian Portal

Introduction

The Cambrian ( /ˈkæmbri.ən, ˈkeɪm-/ KAM-bree-ən, KAYM-; sometimes symbolized Ꞓ) is the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordovician Period 485.4 Ma. 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 Latin name for 'Cymru' (Wales), where Britain's Cambrian rocks are best exposed. Sedgwick identified the layer as part of his task, along with Roderick Murchison, to subdivide the large "Transition Series", although the two geologists disagreed for a while on the appropriate categorization. (Full article...)

Show new selections below (purge)

Selected natural world article

The molluscs or mollusks, compose the large phylum of invertebrate animals known as the phylum Mollusca. Around 85,000 extant species of molluscs are recognized. Molluscs are the largest marine phylum, comprising about 23% of all the named marine organisms. Numerous molluscs also live in freshwater and terrestrial habitats. They are highly diverse, not only in size and in anatomical structure, but also in behaviour and in habitat. The phylum is typically divided into 9 or 10 taxonomic classes, of which two are entirely extinct. Cephalopod molluscs, such as squid, cuttlefish and octopus, are among the most neurologically advanced of all invertebrates—and either the giant squid or the colossal squid is the largest known invertebrate species. The gastropods (snails and slugs) are by far the most numerous molluscs in terms of classified species. The scientific study of molluscs is called malacology. The three most universal features defining modern molluscs are a mantle with a significant cavity used for breathing and excretion, the presence of a radula, and the structure of the nervous system.

Good evidence exists for the appearance of gastropods, cephalopods and bivalves in the Cambrian period 538.8 to 485.4 million years ago. However, the evolutionary history both of molluscs' emergence from the ancestral Lophotrochozoa and of their diversification into the well-known living and fossil forms are still subjects of vigorous debate among scientists. (see more...)

Did you know...

... that Kendallina, a genus of trilobite, lived in North America during the Upper Cambrian?
... that species of the Cambrian bivalve Tuarangia lived near the continents of Baltica and East Gondwana?
... that a revolution in burrowing marks the base of the Cambrian period, and is followed by the Cambrian explosion of animal diversity?
... that the discovery of 189 fossils of the mid-Cambrian Odontogriphus thrust it into the centre of a heated debate about the evolution of molluscs, annelids and brachiopods?
... that August 2009 heralded the 100th anniversary of the discovery of the main Burgess Shale locality?

Need help?

Do you have a question about Abyssal/Portal:Cambrian that you can't find the answer to?

Consider asking it at the Wikipedia reference desk.

Selected image

Opabinia regalis, an enigmatic animal from the middle Cambrian Burgess Shale of British Columbia.
Photo credit: Nobu Tamura

Selected science, culture, and economics article

The geologic map of Georgia (a state within the United States) is a special-purpose map made to show geological features. Rock units or geologic strata are shown by colors or symbols to indicate where they are exposed at the surface. Structural features such as faults and shear zones are also shown. Since the first national geological map, in 1809, there have been numerous maps which included the geology of Georgia. The first Georgia specific geologic map was created in 1825. The most recent state-produced geologic map of Georgia, by the Georgia Department of Natural Resources is 1:500,000 scale, and was created in 1976 by the department's Georgia Geological Survey. It was generated from a base map produced by the United States Geological Survey. The state geologist and Director of the Geological Survey of Georgia was Sam M. Pickering, Jr. Since 1976, several geological maps of Georgia, featuring the state's five distinct geologic regions, have been produced by the federal government. (see more...)