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Saturday, February 10, 2007

today's blog is about the jurassic period !

The Jurassic
The Jurassic Period of the Mesozoic Era: 200 to 146 million years ago.


Introduction
The second of the three divisions that make up the Mesozoic era, the Jurassic period saw warm tropical greenhouse conditions world-wide, shallow continental seas, the break-up of Pangea, cosmopolitan flora and fauna, and the triumph of the majestic dinosaurs and the great sea reptiles.
The name Jurassic comes from the Jura Mountains on the border of France and Switzerland (actually an extension of the Alps into eastern France), where rocks of this age were first studied. In 1795 Alexander von Humbolt described massive limestone formations of the Jura Mountains in Switzerland as the Calcaire de Jura, or Jura-Kalkstein ("Jura Limestone"), which he wrongly believed were older than the (Triassic) Muschelkalk. Between 1796 and 1815 William Smith published geological maps featuring strata that were referred to by William Buckland in 1818 as the Oolite Formation or Oolitic Series. These were divided into Lower, Middle and Upper Oolites. In 1822 Conybeare and Phillips named the underlying strata as the Lias. From this Alexander Brongniart used the term Terrains Jurassiques, although only for the "Lower Oolite" The names Lias and Oolites continued to be used in Britain until quite recently.
In 1839 Leopold von Buch formally named the rocks described by von Humbolt as the Jurassic System, from whence the term has come into general use.
The immense wealth of fossils in Jurassic sediments of Britain (especially ammonites) meant that biostratigraphic zonation was further advanced for Jurassic sediments than for other periods. The terms used to divide the Jurassic Period into early, middle and late - Lias, Dogger, and Malm, are ones that originally referred only to English sediments.
The fact that the remains of many dinosaur and sea reptile remains have been found from the early nineteenth century on contributed to the Victorian imagination regarding "antediluvian monsters."Much more recently, the word Jurassic has become a household word with the success of Speilberg's rather absurd movie about genetically resurrected dinosaurs, Jurassic Park, based on a disappointing novel by Michael Crichton of the same name (actually the novel starts out quite well, but quickly slides into fantasy). Ironically most of dinosaurs featured in Jurassic Park actually lived during the following, Cretaceous, period. But then Cretaceous Park just doesn't have the same ring now, does it.

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