User:Abyssal/Portal:Cambrian

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The Cambrian Portal

Introduction

The Cambrian ( /ˈkæmbri.ən, ˈkeɪm-/ KAM-bree-ən, KAYM-) is the first geological period of the Paleozoic Era, and 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.

Most of the continents lay in the southern hemisphere surrounded by the vast Panthalassa Ocean. The assembly of Gondwana during the Ediacaran and early Cambrian led to the development of new convergent plate boundaries and continental-margin arc magmatism along its margins that helped drive up global temperatures. Laurentia lay across the equator, separated from Gondwana by the opening Iapetus Ocean. (Full article...)

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Life restoration of Marella, the most common animal in the Burgess Shale. — Life restoration of *Marella*, the most common animal in the Burgess Shale.

The fossils of the Burgess Shale, like the Burgess Shale itself, formed around 505 million years ago in the Mid Cambrian period. They were discovered in Canada in 1886, and Charles Doolittle Walcott collected over 60,000 specimens in a series of field trips up from 1909 to 1924. After a period of neglect from the 1930s to the early 1960s, new excavations and re-examinations of Walcott's collection resumed and paleontologists continue to discover new species. These fossils have been preserved in a distinctive style known as Burgess shale type preservation, which preserves fairly tough tissues such as cuticle as thin films and soft tissues as solid shapes.

In the 1970s and early 1980s the Burgess fossils were largely regarded as evidence that the familiar phyla of animals appeared very rapidly in the Early Cambrian, in what is often called the Cambrian explosion. This view was already known to Charles Darwin, who regarded it as one of the greatest difficulties for the theory of evolution he presented in The Origin of Species. However, from the early 1980s the cladistics method of analysing "evolutionary family trees" has persuaded most researchers that many of the Burgess Shale's "weird wonders", such as Opabinia and Hallucinogenia, were evolutionary relatives of modern animal groups rather than a rapid proliferation of separate phyla, some of which were short-lived. Nevertheless there is still debate, sometimes vigorous, about the relationships between some groups of animals. (see more...)

Did you know...

... that the 500-million-year-old Cambrian predator Hurdia was thought to be a number of separate organisms for 100 years, until the complete animal was reconstructed in March 2009?
... that the shrimp-like 510-million-year-old arthropod Waptia was named after two mountains?
... that Orsten, fossil-bearing lagerstätten in Sweden and elsewhere, are called "stinking stones" from organic content that has been preserved since the Cambrian Period?
... that the fordilloid Camya asy is one of four accepted Cambrian bivalves?
...that despite being known from many specimens, the fossil Fuxianhuia (pictured) remains one of the most controversial Cambrian arthropods?

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Nectocaris pteryx after the reconstruction in Smith & Caron 2010.
Photo credit: User:Citron

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Oil shale, also known as kerogen shale, is an organic-rich fine-grained sedimentary rock containing kerogen (a solid mixture of organic chemical compounds) from which liquid hydrocarbons called shale oil can be produced. Shale oil is a substitute for conventional crude oil; however, extracting shale oil from oil shale is more costly than the production of conventional crude oil both financially and in terms of its environmental impact. Deposits of oil shale occur around the world. Estimates of global deposits range from 2.8 to 3.3 trillion barrels (450×10⁹ to 520×10⁹ m³) of recoverable oil.

Heating oil shale to a sufficiently high temperature causes the chemical process of pyrolysis to yield a vapor. Upon cooling the vapor, the liquid shale oil—an unconventional oil—is separated from combustible oil-shale gas (the term shale gas can also refer to gas occurring naturally in shales). Oil shale can also be burned directly in furnaces as a low-grade fuel for power generation and district heating or used as a raw material in chemical and construction-materials processing.

Oil-shale mining and processing raise a number of environmental concerns, such as land use, waste disposal, water use, waste-water management, greenhouse-gas emissions and air pollution. Estonia and China have well-established oil shale industries, and Brazil, Germany, and Russia also utilize oil shale. (see more...)