User:Abyssal/Portal:Ordovician
IntroductionThe Ordovician (/ɔːrdəˈvɪʃi.ən, -doʊ-, -ˈvɪʃən/ or-də-VISH-ee-ən, -doh-, -VISH-ən) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period 485.4 Ma (million years ago) to the start of the Silurian Period 443.8 Ma. The Ordovician, named after the Welsh tribe of the Ordovices, was defined by Charles Lapworth in 1879 to resolve a dispute between followers of Adam Sedgwick and Roderick Murchison, who were placing the same rock beds in North Wales in the Cambrian and Silurian systems, respectively. Lapworth recognized that the fossil fauna in the disputed strata were different from those of either the Cambrian or the Silurian systems, and placed them in a system of their own. The Ordovician received international approval in 1960 (forty years after Lapworth's death), when it was adopted as an official period of the Paleozoic Era by the International Geological Congress. Life continued to flourish during the Ordovician as it did in the earlier Cambrian Period, although the end of the period was marked by the Ordovician–Silurian extinction events. Invertebrates, namely molluscs and arthropods, dominated the oceans, with members of the latter group probably starting their establishment on land during this time, becoming fully established by the Devonian. The first land plants are known from this period. The Great Ordovician Biodiversification Event considerably increased the diversity of life. Fish, the world's first true vertebrates, continued to evolve, and those with jaws may have first appeared late in the period. About 100 times as many meteorites struck the Earth per year during the Ordovician compared with today. (Full article...) Selected article on the Ordovician world and its legacies![]() There are approximately 5×1030 bacteria on Earth, forming a biomass that exceeds that of all plants and animals. Bacteria are vital in recycling nutrients, with many steps in nutrient cycles depending on these organisms, such as the fixation of nitrogen from the atmosphere and putrefaction. In the biological communities surrounding hydrothermal vents and cold seeps, bacteria provide the nutrients needed to sustain life by converting dissolved compounds such as hydrogen sulphide and methane to energy. Most bacteria have not been characterised, and only about half of the phyla of bacteria have species that can be grown in the laboratory. The study of bacteria is known as bacteriology, a branch of microbiology. Unlike cells of animals and other eukaryotes, bacterial cells do not contain a nucleus and rarely harbour membrane-bound organelles. (see more...) Selected article on the Ordovician in human science, culture and economics![]() In 1858, Charles Darwin and Alfred Russel Wallace published a new evolutionary theory that was explained in detail in Darwin's On the Origin of Species (1859). Unlike Lamarck, Darwin proposedcommon descent and a branching tree of life. The theory was based on the idea of natural selection, and it synthesized a broad range of evidence from animal husbandry, biogeography, geology, morphology, and embryology. The debate over Darwin's work led to the rapid acceptance of the general concept of evolution, but the specific mechanism he proposed, natural selection, was not widely accepted until it was revived by developments in biology that occurred during the 1920s through the 1940s. Before that time most biologists argued that other factors were responsible for evolution. The synthesis of natural selection with Mendelian genetics during the 1920s and 1930s founded the new discipline of population genetics. Throughout the 1930s and 1940s, population genetics became integrated with other biological fields, resulting in a widely applicable theory of evolution that encompassed much of biology—the modern evolutionary synthesis. (see more...) Selected image
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Need help?Do you have a question about Abyssal/Portal:Ordovician that you can't find the answer to? Consider asking it at the Wikipedia reference desk. TopicsEpochs - Early Ordovician - Middle Ordovician - Late Ordovician Landmasses - Baltica - Gondwana - Laurentia - Siberia Fossil sites - Beecher's Trilobite Bed - Walcott–Rust quarry Researchers - Charles Emerson Beecher - Charles Lapworth - Charles Doolittle Walcott Quality ContentFeatured Ordovician articles - None SubcategoriesRelated contentAssociated WikimediaThe following Wikimedia Foundation sister projects provide more on this subject:
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