Cambrian

The Cambrian (/ˈkæmbriən/ or /ˈkeɪmbriən/) is the first geological period of the Paleozoic Era, lasting from 541 to 485.4 million years ago (mya) and is succeeded by the Ordovician. Its subdivisions, and indeed 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. These are sites of exceptional preservation, where "soft" parts of organisms are preserved as well as their more resistant shells. This means that our understanding of the Cambrian biology surpasses that of some later periods.

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.

Cambrian explosion

The Cambrian explosion, or less commonly Cambrian radiation, was the relatively short evolutionary event, beginning around 542 million years ago in the Cambrian Period, during which most major animal phyla appeared, as indicated by the fossil record. Lasting for about the next 20–25 million years, it resulted in the divergence of most modern metazoan phyla. Additionally, the event was accompanied by major diversification of other organisms. Prior to the Cambrian explosion, most organisms were simple, composed of individual cells occasionally organized into colonies. Over the following 70 to 80 million years, the rate of diversification accelerated by an order of magnitude and the diversity of life began to resemble that of today. Many of the present phyla appeared during this period, with the exception of Bryozoa, which made its earliest known appearance in the Lower Ordovician.

The Cambrian explosion has generated extensive scientific debate. The seemingly rapid appearance of fossils in the “Primordial Strata” was noted as early as the 1840s, and in 1859 Charles Darwin discussed it as one of the main objections that could be made against the theory of evolution by natural selection. The long-running puzzlement about the appearance of the Cambrian fauna, seemingly abruptly and from nowhere, centers on three key points: whether there really was a mass diversification of complex organisms over a relatively short period of time during the early Cambrian; what might have caused such rapid change; and what it would imply about the origin of animal life. Interpretation is difficult due to a limited supply of evidence, based mainly on an incomplete fossil record and chemical signatures remaining in Cambrian rocks.

The Cambrian

The Cambrian, a weekly started by George Haynes and L. W. Dillwyn in 1804, was the first newspaper published in Wales. Its original publisher was Thomas Jenkins. The full masthead proclaimed The Cambrian and Weekly General Advertiser for Swansea and the Principality of Wales. By 1906 it was acquired by South Wales Post Newspapers Co. and, in 1930, merged with Herald of Wales.

References

The Atheist Experience

The Atheist Experience, a weekly webcast and cable access television show in Austin, Texas, first aired on October 19, 1997. Rotating regulars Matt Dillahunty,Jeff Dee, Martin Wagner, Russell Glasser, Don Baker, Tracie Harris, Jen Peeples, and John Iacoletti host and co-host the program. Frequent topics include religious dogma, morality, ethics and application of the scientific method. The co-host often opens with a theme or current event, then takes live calls. Although debate about all theist and atheist-related views are welcome, because of the large number of Christians in the United States, the emphasis is mostly on Christianity.

The Atheist Experience is broadcast by the Atheist Community of Austin (ACA), an educational non-profit organization based in Austin, Texas. The ACA has as a central goal the promotion of positive atheism and of the separation of church and state.

A YouTube channel which became the official channel in August 2012 has over 127,055 subscribers and over 20.03 million video views as of June 2015.

Atheist (disambiguation)

An atheist is a person who does not believe in the existence of deity. A "strong atheist" is a person who rejects the belief in a deity.

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See also