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Biodiversity is the variety of different types of life found on the Earth and the variations within species.〔(【引用サイトリンク】title=What is biodiversity? )〕 It is a measure of the variety of organisms present in different ecosystems. This can refer to genetic variation, ecosystem variation, or species variation (number of species)〔 within an area, biome, or planet. Terrestrial biodiversity tends to be greater near the equator, which seems to be the result of the warm climate and high primary productivity. Biodiversity is not distributed evenly on Earth. It is richest in the tropics. Marine biodiversity tends to be highest along coasts in the Western Pacific, where sea surface temperature is highest and in the mid-latitudinal band in all oceans. There are latitudinal gradients in species diversity. Biodiversity generally tends to cluster in hotspots, and has been increasing through time but will be likely to slow in the future. The number and variety of plants, animals and other organisms that exist is known as biodiversity. It is an essential component of nature and it ensures the survival of human species by providing food, fuel, shelter, medicines and other resources to mankind. The richness of biodiversity depends on the climatic conditions and area of the region. All species of plants taken together are known as flora and about 70,000 species of plants are known till date. All species of animals taken together are known as fauna which includes birds, mammals, fish, reptiles, insects, crustaceans, molluscs, etc. Rapid environmental changes typically cause mass extinctions. More than 99 percent of all species, amounting to over five billion species, that ever lived on Earth are estimated to be extinct. Estimates on the number of Earth's current species range from 10 million to 14 million, of which about 1.2 million have been documented and over 86 percent have not yet been described. The total amount of related DNA base pairs on Earth is estimated at 5.0 x 1037, and weighs 50 billion tonnes. In comparison, the total mass of the biosphere has been estimated to be as much as 4 TtC (trillion tons of carbon). The age of the Earth is about 4.54 billion years old.〔 〕 The earliest undisputed evidence of life on Earth dates at least from 3.5 billion years ago,〔Schopf, JW, Kudryavtsev, AB, Czaja, AD, and Tripathi, AB. (2007). ''Evidence of Archean life: Stromatolites and microfossils.'' Precambrian Research 158:141–155.〕〔Schopf, JW (2006). ''Fossil evidence of Archaean life.'' Philos Trans R Soc Lond B Biol Sci 29;361(1470) 869-85.〕 during the Eoarchean Era after a geological crust started to solidify following the earlier molten Hadean Eon. There are microbial mat fossils found in 3.48 billion-year-old sandstone discovered in Western Australia. Other early physical evidence of a biogenic substance is graphite in 3.7 billion-year-old metasedimentary rocks discovered in Western Greenland. More recently, in 2015, "remains of biotic life" were found in 4.1 billion-year-old rocks in Western Australia.〔 Early edition, published online before print.〕 According to one of the researchers, "If life arose relatively quickly on Earth ... then it could be common in the universe."〔 Since life began on Earth, five major mass extinctions and several minor events have led to large and sudden drops in biodiversity. The Phanerozoic eon (the last 540 million years) marked a rapid growth in biodiversity via the Cambrian explosion—a period during which the majority of multicellular phyla first appeared.〔(【引用サイトリンク】title=The Cambrian Period )〕 The next 400 million years included repeated, massive biodiversity losses classified as mass extinction events. In the Carboniferous, rainforest collapse led to a great loss of plant and animal life. The Permian–Triassic extinction event, 251 million years ago, was the worst; vertebrate recovery took 30 million years. The most recent, the Cretaceous–Paleogene extinction event, occurred 65 million years ago and has often attracted more attention than others because it resulted in the extinction of the dinosaurs. The period since the emergence of humans has displayed an ongoing biodiversity reduction and an accompanying loss of genetic diversity. Named the Holocene extinction, the reduction is caused primarily by human impacts, particularly habitat destruction. Conversely, biodiversity impacts human health in a number of ways, both positively and negatively. The United Nations designated 2011–2020 as the United Nations Decade on Biodiversity. ==Etymology== The term biological diversity was used first by wildlife scientist and conservationist Raymond F. Dasmann in the year 1968 lay book ''A Different Kind of Country''〔 Dasmann, R. F. 1968. A Different Kind of Country. MacMillan Company, New York. ISBN 0-02-072810-7.〕 advocating conservation. The term was widely adopted only after more than a decade, when in the 1980s it came into common usage in science and environmental policy. Thomas Lovejoy, in the foreword to the book ''Conservation Biology'',〔 M. E. Soulé and B. A. Wilcox. 1980. Conservation Biology: An Evolutionary-Ecological Perspective. Sinauer Associates. Sunderland, Massachusetts.〕 introduced the term to the scientific community. Until then the term "natural diversity" was common, introduced by The Science Division of The Nature Conservancy in an important 1975 study, "The Preservation of Natural Diversity." By the early 1980s TNC's Science program and its head, Robert E. Jenkins, Lovejoy and other leading conservation scientists at the time in America advocated the use of the term "biological diversity". The term's contracted form ''biodiversity'' may have been coined by W.G. Rosen in 1985 while planning the 1986 ''National Forum on Biological Diversity'' organized by the National Research Council (NRC). It first appeared in a publication in 1988 when sociobiologist E. O. Wilson used it as the title of the proceedings〔 Edward O.Wilson, editor, Frances M.Peter, associate editor, ''Biodiversity'', National Academy Press, March 1988 ISBN 0-309-03783-2 ; ISBN 0-309-03739-5 (pbk.), (online edition )〕 of that forum.〔 Global Biodiversity Assessment. UNEP, 1995, Annex 6, Glossary. ISBN 0-521-56481-6, used as source by ("Biodiversity", Glossary of terms related to the CBD ), Belgian Clearing-House Mechanism. Retrieved 2006-04-26.〕 Since this period the term has achieved widespread use among biologists, environmentalists, political leaders, and concerned citizens. A similar term in the United States is ''"natural heritage."'' It pre-dates the others and is more accepted by the wider audience interested in conservation. Broader than biodiversity, it includes geology and landforms. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「biodiversity」の詳細全文を読む スポンサード リンク
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