Jurassic period
Jurassic period
| Noun | 1. Jurassic period - from 190 million to 135 million years ago; dinosaurs; conifers |
| 单词 | jurassic period | ||
| 释义 | Jurassic periodJurassic period
Jurassic periodSee also: Geologic Timescale (table)Geologic Timescale Jurassic period(jərăs`ĭk) [from the Jura Mts.], second period of the Mesozoic eraMesozoic era[Gr.,=middle life], major division of geologic time (see Geologic Timescale, table) from 65 to 225 million years ago. Great crustal disturbances that marked the close of the Paleozoic and the beginning of the Mesozoic eras brought about drastic changes in the ..... Click the link for more information. of geologic time, lasting from 213 to 144 million years ago. At the start of the Jurassic most of the continents were joined together until the Atlantic began to form and the Americas split off from Africa. Eastern North America was mostly elevated and subject to erosion, which reduced the Appalachian region to a peneplain. Before the end of the period, the Appalachian borderland began to founder as the Atlantic Ocean continued to widen. The Pacific border of North America, from California to Alaska, was submerged for most of the period. In the Early Jurassic, large areas of Arizona, Colorado, and Utah were apparently desert, and the sand was later consolidated into the white and pinkish Glen Canyon and Navajo sandstones, which now enhance the scenic beauty of the district. During the Upper Jurassic, the Logan Sea entered this area from the north. In its various advances and retreats, this body of water covered large areas of Montana, Idaho, Wyoming, Colorado, and Utah, depositing sandstone, shale, limestone, and some gypsum. The retreat of the Logan Sea, toward the end of the period, was followed, probably in the Upper Jurassic but possibly in the Lower Cretaceous Period, by the deposition of the Morrison continental series of clays and sandstones, noted for its richness in fossil dinosaurs. The close of the Jurassic in North America was marked by widespread folding along the western border of the continent, accompanied by the intrusion of lava as the eastern edge of the plate that carries the Pacific Ocean was thrust beneath the westward drifting plate that carries the North American continent. In this disturbance the Sierra Nevada, Klamaths, Cascades, Coast Ranges, and coastal mountains of Canada and Alaska were formed. The history of the European Jurassic is very well known, that system being one of the most complete on the Continent. Studies of oxygen isotopes, the extent of land flora, and marine fossils indicate that climates during Jurassic times were mild—perhaps 15°F; (8°C;) warmer than those of today. No glaciers existed during this period. The plant life of the Jurassic was dominated by the cycadscycad , any plant of the order Cycadales, tropical and subtropical palmlike evergreens. The cycads, ginkgoes, and conifers comprise the three major orders of gymnosperms, or cone-bearing plants (see cone and plant). The cycads first appeared in the Permian period. ..... Click the link for more information. , but conifersconifer [Lat.,=cone-bearing], tree or shrub of the order Coniferales, e.g., the pine, monkey-puzzle tree, cypress, and sequoia. Most conifers bear cones and most are evergreens, though a few, such as the larch, are deciduous. ..... Click the link for more information. , ginkgoesginkgo or maidenhair tree, tall, slender, picturesque deciduous tree (Ginkgo biloba) with fan-shaped leaves. The ginkgo is native to E China, where it was revered by Buddhist monks and planted near temples. ..... Click the link for more information. , horsetailshorsetail, any plant of the genus Equisetum [Lat.,=horse bristle], the single surviving genus of a large group (Equisetophyta) of primitive vascular plants. Like the ferns and club mosses, relatives of the living horsetails thrived in the Carboniferous period (when they ..... Click the link for more information. , and fernsfern, any plant of the division Polypodiophyta. Fern species, numbering several thousand, are found throughout the world but are especially abundant in tropical rain forests. The ferns and their relatives (e.g. ..... Click the link for more information. were also abundant. Of the marine invertebrates, the most important were the ammonites. The dominant animals on land, in the sea, and in the air were the reptiles. Dinosaursdinosaur [Gr., = terrible lizard], extinct land reptile of the Mesozoic era. The dinosaurs, which were egg-laying animals, ranged in length from 2 1-2 ft (91 cm) to about 127 ft (39 m). ..... Click the link for more information. , more numerous and more extraordinary than those of the Triassic period, were the chief land animals; crocodiles, ichthyosaurs, and plesiosaurs ruled the sea, while the air was inhabited by the pterosaurspterosaur [Gr., = winged lizard], extinct flying reptile (commonly called pterodactyl [Gr., = wing finger]) of the order Pterosauria, common in the late Triassic and Cretaceous periods, from approximately 228 to 65 million years ago. ..... Click the link for more information. and relatives. Mammals, making their first appearance, were few and small but undoubtedly became well established during the Jurassic period. The Jurassic also saw the appearance of ArchaeopteryxArchaeopteryx [Gr.,=primitive wing], a 150 million-year-old fossil animal first discovered in 1860 in the late Jurassic limestone of Solnhofen, Bavaria, and described the following year. ..... Click the link for more information. . 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). Jurassic periodJurassic perioda period of the MESOZOIC ERA that lasted from 200 to 135 million years ago, during which time the birds evolved. Cycads, ferns and conifers were widespread. Dinosaurs were dominant and the first fossil moth was recorded from this period. Pangea began to break up and the site of London was at 30 °N.Jurassic period
Synonyms for Jurassic period
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