Devonian period
Devonian period
| Noun | 1. |  Devonian period - from 405 million to 345 million years ago; preponderance of fishes and appearance of amphibians and ammonites |
| 单词 | devonian period | |||
| 释义 | Devonian periodDevonian period
Devonian periodSee also: Geologic Timescale (table)Geologic Timescale Devonian period(dĭvō`nēən), fourth period of the Paleozoic eraPaleozoic era, a major division (era) of geologic time (see Geologic Timescale, table) occurring between 570 to 240 million years ago. It is subdivided into six periods, the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian (see each listed individually). ..... Click the link for more information. of geologic time between 408 and 360 million years ago (see Geologic TimescaleGeologic Timescale Era Period Epoch Approximate duration (millions of years) Approximate number of years ago (millions of years) Cenozoic Quaternary Holocene 10,000 years ago to the present Pleistocene 2 . ..... Click the link for more information. , table). It was named (1838) by the geologists Sir Roderick Impey MurchisonMurchison, Sir Roderick Impey , 1792–1871, British geologist. He served in the Napoleonic Wars but after the peace turned his attention to science. In the 1830s he undertook the investigation of previously undifferentiated rock strata in Wales and England; as a result of ..... Click the link for more information. and Adam SedgwickSedgwick, Adam, 1785–1873, English geologist. He was a professor at Cambridge from 1818. His most important work was a study, made with R. I. Murchison, of the rock formation of Devonshire, which they named the Devonian system. Sedgwick also introduced the term Cambrian. ..... Click the link for more information. for Devonshire, England, where they first investigated rocks formed during the period. The Devonian period was a time of great tectonic activity, as Laurasia and Gondwanaland drew closer together. Pangaea began to consolidate the plates containing North America and Europe (see plate tectonicsplate tectonics, theory that unifies many of the features and characteristics of continental drift and seafloor spreading into a coherent model and has revolutionized geologists' understanding of continents, ocean basins, mountains, and earth history. ..... Click the link for more information. ), further raising the northern Appalachian Mountains and forming the Caledonides in Britain and Scandinavia. For much of the Devonian, large areas of North America and Europe, and smaller parts of Africa, South America, and Australia were covered by seas, which withdrew during the Upper Devonian. The Cordilleran area of North America was submerged, depositing from 4,000 to 6,000 ft (1,200–1,800 m) of limestone and shale in Nevada and 2,400 ft (730 m) of quartzites and limestones in Utah. The Devonian period in Europe was marked by considerable volcanic activity and the deposition of two great rock systems: the marine formation of Devonshire, the Rhine valley, and Russia; and the Old Red SandstoneOld Red Sandstone, series of red and brown sandstones, conglomerates, and shales deposited in Wales and Scotland and in England near the Welsh and Scottish borders in the Devonian period of geologic time. ..... Click the link for more information. . The climate was relatively warm everywhere on the earth. The most notable Devonian animals were the jawed and bony fishes, which appeared in great numbers toward the close of the period. Conspicuous types were sharks, armored fishes, lungfishes, and ganoid fishes. Common invertebrates of the Devonian were crinoids, starfishes, sponges, and early ammonites; trilobites and graptolites became scarcer. An unusual surge of coral reef growth also occurred and corals were never again as prolific. Of land animals, the chief vestige is the footprint of a primitive salamanderlike amphibian in the Upper Devonian of Pennsylvania. Trees made their first appearance; the Devonian plants were the earliest to be extensively preserved as fossils, but their high degree of development suggests that more primitive forms existed earlier. Devonian periodDevonian perioda geological period lasting from about 415 to 370 million years ago. Many freshwater fish existed during this period and plants became established on land. True seed plants evolved and lycopods reached the size of trees. Amphibians evolved, the first known insects, spiders and mites occurred and most graptolites became extinct. Britain still lay south of the equator with the Thames at 10 °S. See GEOLOGICAL TIME.Devonian period
Synonyms for Devonian period
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