Guizhou, is a province of the People's Republic of China located in the southwestern part of the country. Its capital city is Guiyang. Guizhou is a poor and economically undeveloped province, but rich in natural and environmental resources. Demographically it is one of China's most diverse provinces. Minority groups account for more than 37% of the population; the area was first organized as an administrative region of a Chinese empire under the Tang, when it was named Juzhou, pronounced Kjú-jyuw in the Middle Chinese of the period. During the Mongolian Yuan dynasty, the character 矩 was changed to the more refined 貴; the region formally became a province in 1413, with an eponymous capital also called "Guizhou" but now known as Guiyang. Another single-character abbreviation is "黔". Evidence of settlement by humans during the Middle Palaeolithic is indicated by stone artefacts, including Levallois pieces, found during archaeological excavations at Guanyindong Cave; these artefacts have been dated to 170,000–80,000 years ago using optically stimulated luminescence methods.
From around 1046 BC to the emergence of the State of Qin, northwest Guizhou was part of the State of Shu. During the Warring States period, the Chinese state of Chu conquered the area, control passed to the Dian Kingdom. During the Chinese Han Dynasty, to which the Dian was tributary, Guizhou was home to the Yelang collection of tribes, which governed themselves before the Han consolidated control in the southwest and established the Lingnan province. During the Three Kingdoms period, parts of Guizhou were governed by the Shu Han state based in Sichuan, followed by Cao Wei and the Jin Dynasty. During the 8th and 9th centuries in the Tang dynasty, Chinese soldiers moved into Guizhou and married native women, their descendants are known as Lǎohànrén, in contrast to new Chinese who populated Guizhou at times. They still speak an archaic dialect. Many immigrants to Guizhou were descended from these soldiers in garrisons who married these pre-Chinese women. Kublai Khan and Möngke Khan conquered the Chinese southwest in the process of defeating the Song during the Mongol invasion of China, the newly established Yuan dynasty saw the importation of Chinese Muslim administrators and settlers from Bukhara in Central Asia.
It was during the following Ming dynasty, once again led by Han Chinese, that Guizhou was formally made a province in 1413. The Ming established many garrisons in Guizhou from which to pacify the Yao and Miao minorities during the Miao Rebellions. Chinese-style agriculture flourished with the expertise of farmers from Sichuan and its surrounding provinces into Guizhou. Wu Sangui was responsible for the ousting the Ming in Guizhou and Yunnan during the Manchu conquest of China. During the governorship-general of the Qing Dynasty's nobleman Ortai, the tusi system of indirect governance of the southwest was abolished, prompting rebellions from disenfranchised chieftains and the further centralization of government. After the Second Opium War, criminal triads set up shop in Guangxi and Guizhou to sell British opium. For a time, Taiping Rebels took control of Guizhou, but they were suppressed by the Qing. Concurrently, Han Chinese soldiers moved into the Taijiang region of Guizhou, married Miao women, their children were brought up as Miao.
More unsuccessful Miao rebellions occurred during the Qing, in 1735, from 1795–1806 and from 1854–1873. After the overthrow of the Qing in 1911 and following Chinese Civil War, the Communists took refuge in Guizhou during the Long March. While the province was formally ruled by the Guomindang warlord Wang Jialie, the Zunyi Conference in Guizhou established Mao Zedong as the leader of the Communist Party; as the Second Sino-Japanese War pushed China's Nationalist Government to its southwest base of Chongqing, transportation infrastructure improved as Guizhou was linked with the Burma Road. After the end of the War, a 1949 Revolution swept Mao into power, who promoted the relocation of heavy industry into inland provinces such as Guizhou, to better protect them from Soviet and American attacks. After the Chinese economic reform began in 1978, geographical factors led Guizhou to become the poorest province in China, with a GDP growth average of 9 percent from 1978–1993. Guizhou is a mountainous province, although its higher altitudes are in the centre.
It lies at the eastern end of the Yungui Plateau. At 2,900 m meters above sea level, Jiucaiping is Guizhou's highest point. Guizhou has a humid subtropical climate. There are few seasonal changes, its annual average temperature is 10 to 20 °C, with January temperatures ranging from 1 to 10 °C and July temperatures ranging from 17 to 28 °C. Like in China's other southwest provinces, rural areas of Guizhou suffered severe drought during spring 2010. One of China's poorest provinces, Guizhou is experiencing serious environmental problems, such as desertification and persistent water shortages. On 3–5 April 2010, China's Premier Wen Jiabao went on a three-day inspection tour in the southwest drought-affected province of Guizhou, where he met villagers and called on agricultural scientists to develop drought-resistant technologies for the area; the border mountains of Guizhou and Hunan have been identified as one of the eight plant diversity hotspots in China. The main ecosystem types include evergreen broad-leaved forest and broad-leaved mixed forest, montane elfin forest.
Plant species endemic to this region include Abies ziyuanensis, Cathaya argyrophylla, Keteleeria pubescens. In broad terms, the Yunna
Lignite referred to as brown coal, is a soft, combustible, sedimentary rock formed from compressed peat. It is considered the lowest rank of coal due to its low heat content, it has a carbon content around 60–70 percent. It is mined all around the world, is used exclusively as a fuel for steam-electric power generation, is the coal, most harmful to health. Lignite is brownish-black in color and has a carbon content around 60–70 percent, a high inherent moisture content sometimes as high as 75 percent, an ash content ranging from 6–19 percent compared with 6–12 percent for bituminous coal; the energy content of lignite ranges from 10 to 20 MJ/kg on a mineral-matter-free basis. The energy content of lignite consumed in the United States averages 15 MJ/kg, on the as-received basis; the energy content of lignite consumed in Victoria, averages 8.4 MJ/kg. Lignite has a high content of volatile matter which makes it easier to convert into gas and liquid petroleum products than higher-ranking coals, its high moisture content and susceptibility to spontaneous combustion can cause problems in transportation and storage.
It is now known that efficient processes which remove latent moisture locked within the structure of brown coal will relegate the risk of spontaneous combustion to the same level as black coal, transform the calorific value of brown coal to a black coal equivalent fuel, reduce the emissions profile of'densified' brown coal to a level similar to or better than most black coals. However, removing the moisture increases the cost of the final lignite fuel; because of its low energy density and high moisture content, brown coal is inefficient to transport and is not traded extensively on the world market compared with higher coal grades. It is burned in power stations near the mines, such as in Australia's Latrobe Valley and Luminant's Monticello plant in Texas; because of latent high moisture content and low energy density of brown coal, carbon dioxide emissions from traditional brown-coal-fired plants are much higher per megawatt generated than for comparable black-coal plants, with the world's highest-emitting plant being Hazelwood Power Station until its closure in March 2017.
The operation of traditional brown-coal plants in combination with strip mining, can be politically contentious due to environmental concerns. In 2014, about 12 percent of Germany's energy and 27 percent of Germany's electricity came from lignite power plants, while in 2014 in Greece, lignite provided about 50 percent of its power needs. An environmentally beneficial use of lignite can be found in its use in cultivation and distribution of biological control microbes that suppress plant disease causing microbes; the carbon enriches the organic matter in the soil while the biological control microbes provide an alternative to chemical pesticides. Reaction with quaternary amine forms a product called amine-treated lignite, used in drilling mud to reduce fluid loss during drilling. Lignite begins as an accumulation of decayed plant material, or peat. Burial by other sediments results in increasing temperature, depending on the local geothermal gradient and tectonic setting, increasing pressure.
This causes compaction of the loss of some of the water and volatile matter. This process, called coalification, concentrates the carbon content, thus the heat content, of the material. Deeper burial and the passage of time result in further expulsion of moisture and volatile matter transforming the material into higher-rank coals such as bituminous and anthracite coal. Lignite deposits are younger than higher-ranked coals, with the majority of them having formed during the Tertiary period; the Latrobe Valley in Victoria, contains estimated reserves of some 65 billion tonnes of brown coal. The deposit is equivalent to 25 percent of known world reserves; the coal seams are up to 100 metres thick, with multiple coal seams giving continuous brown coal thickness of up to 230 metres. Seams are covered by little overburden. Lignite can be separated into two types; the first is xyloid lignite or fossil wood and the second form is the compact lignite or perfect lignite. Although xyloid lignite may sometimes have the tenacity and the appearance of ordinary wood, it can be seen that the combustible woody tissue has experienced a great modification.
It is reducible to a fine powder by trituration, if submitted to the action of a weak solution of potash, it yields a considerable quantity of humic acid. Leonardite is an oxidized form of lignite, which contains high levels of humic acid. Jet is a gem-like form of lignite used in various types of jewelry. "Coal and lignite domestic consumption". Global Energy Statistical Yearbook. 2016. Geography in action – an Irish case study Photograph of lignite Coldry:Lignite Dewatering Process Why Brown Coal Should Stay in the Ground Victoria Australia Brown Coal Factsheet Australian mines atlas
Pseudotsuga is a genus of evergreen coniferous trees in the family Pinaceae. Common names include Douglas fir, Douglas-fir, Douglas tree, Oregon pine. Pseudotsuga menziesii is an important source of timber; the number of species has long been debated, but two in western North America and two to four in eastern Asia are acknowledged. Nineteenth-century botanists had problems in classifying Douglas-firs, due to the species' similarity to various other conifers better known at the time; because of their distinctive cones, Douglas-firs were placed in the new genus Pseudotsuga by the French botanist Carrière in 1867. The genus name has been hyphenated as Pseudo-tsuga; the tree takes its English name from David Douglas, the Scottish botanist who first introduced Pseudotsuga menziesii into cultivation at Scone Palace in 1827. Douglas is known for introducing many native American tree species to Europe; the hyphenated form "Douglas-fir" is used by some to indicate that Pseudotsuga species are not true firs, which belong to the genus Abies.
Douglas-firs are medium-size to large evergreen trees, 20–120 metres tall. The leaves are flat, linear, 2–4 centimetres long resembling those of the firs, occurring singly rather than in fascicles; the female cones are pendulous, with persistent scales, are distinctive in having a long tridentine bract that protrudes prominently above each scale. Pseudotsuga menziesii var. menziesii has attained heights of 393 feet. That was the estimated height of the tallest conifer well-documented, the Mineral Tree, measured in 1924 by Dr. Richard E. McArdle, former chief of the U. S. Forest Service; the volume of that tree was 515 cubic metres. The tallest living individual is the Brummitt Fir in Oregon, 99.4 metres tall. Only coast redwood and Eucalyptus regnans reach greater heights based on current knowledge of living trees. At Quinault, Washington, is found a collection of the largest Douglas-firs in one area. Quinault Rain Forest hosts the most of the top ten known largest Douglas-firs; as of 2009, the largest known Douglas-firs in the world are, by volume: Red Creek Tree 12,320 cubic feet Queets Fir 11,710 cubic feet Tichipawa 10,870 cubic feet Rex 10,200 cubic feet Ol' Jed 10,040 cubic feet By far the best-known is the widespread and abundant North American species Pseudotsuga menziesii, a taxonomically complex species divided into two major varieties: coast Douglas-fir or "green Douglas-fir", on the Pacific coast.
According to some botanists, Rocky Mountain Douglas-fir extends south into Mexico to include all Mexican Douglas-fir populations, whereas others have proposed multiple separate species in Mexico and multiple varieties in the United States. Morphological and genetic evidence suggest that Mexican Douglas-fir should be considered a distinct variety within P. menziesii. All of the other species are of restricted range and little-known outside of their respective native environments, where they are rare and of scattered occurrence in mixed forests; the taxonomy of the Asian Douglas-firs continues to be disputed, but the most recent taxonomic treatment accepts four species: three Chinese and one Japanese. The three Chinese species have been variously considered varieties of P. sinensis or broken down into additional species and varieties. In the current treatment, the Chinese species P. sinensis is further subdivided into two varieties: var. sinensis and var. wilsoniana. Pseudotsuga macrocarpa Mayr – bigcone Douglas-fir - southern California Pseudotsuga menziesii Franco - western North America from Alaska to Oaxaca Pseudotsuga menziesii var. glauca Franco – Rocky Mountain Douglas-fir Pseudotsuga menziesii var. menziesii – coast Douglas-fir Pseudotsuga lindleyana Carrière – Mexican Douglas-fir Pseudotsuga brevifolia W.
C. Cheng & L. K. Fu – short-leaf Chinese Douglas-fir Pseudotsuga forrestii Craib – Yunnan Douglas-fir Pseudotsuga japonica Beissn. – Japanese Douglas-fir Pseudotsuga sinensis Dode – Chinese Douglas-fir Pseudotsuga sinensis var. sinensis Pseudotsuga sinensis var. wilsoniana – Taiwan Douglas-fir Keteleeria davidiana Beissn. Cathaya argyrophylla Keteleeria fortunei Abies magnifica Abies procera Douglas-fir wood is used for structural applications that are required to withstand high loads, it is used extensively in the construction industry. Other examples include its use for homebuilt aircraft such as the RJ.03 IBIS canard. These aircraft were designed to utilize Sitka spruce, becoming difficult to source in aviation quality grades. Oregon pine is used in boat building when it is available in long knot-free lengths. Most timber now comes from plantation forests in
A cone is an organ on plants in the division Pinophyta that contains the reproductive structures. The familiar woody cone is the female cone; the male cones, which produce pollen, are herbaceous and much less conspicuous at full maturity. The name "cone" derives from the fact; the individual plates of a cone are known as scales. The male cone is structurally similar across all conifers, differing only in small ways from species to species. Extending out from a central axis are microsporophylls. Under each microsporophyll is several microsporangia; the female cone contains ovules. The female cone structure varies more markedly between the different conifer families, is crucial for the identification of many species of conifers; the members of the pine family have cones. These pine cones the woody female cones, are considered the "archetypal" tree cones; the female cone has two types of scale: the bract scales, the seed scales, one subtended by each bract scale, derived from a modified branchlet. On the upper-side base of each seed scale are two ovules that develop into seeds after fertilization by pollen grains.
The bract scales develop first, are conspicuous at the time of pollination. The scales open temporarily to receive gametophytes close during fertilization and maturation, re-open again at maturity to allow the seed to escape. Maturation takes 6–8 months from pollination in most Pinaceae genera, but 12 months in cedars and 18–24 months in most pines; the cones open either by the seed scales flexing back when they dry out, or by the cones disintegrating with the seed scales falling off. The cones are conic, cylindrical or ovoid, small to large, from 2–60 cm long and 1–20 cm broad. After ripening, the opening of non-serotinous pine cones is associated with their moisture content—cones are open when dry and closed when wet; this assures that the small, wind disseminated seeds will be dispersed during dry weather, thus, the distance traveled from the parent tree will be enhanced. A pine cone will go through many cycles of opening and closing during its life span after seed dispersal is complete; this process occurs with older cones while attached to branches and after the older cones have fallen to the forest floor.
The condition of fallen pine cones is a crude indication of the forest floor's moisture content, an important indication of wildfire risk. Closed cones indicate damp conditions; as a result of this, pine cones have been used by people in temperate climates to predict dry and wet weather hanging a harvested pine cone from some string outside to measure the humidity of the air. Members of the Araucariaceae have the bract and seed scales fused, have only one ovule on each scale; the cones are spherical or nearly so, large to large, 5–30 cm diameter, mature in 18 months. In Agathis, the seeds are winged and separate from the seed scale, but in the other two genera, the seed is wingless and fused to the scale; the cones of the Podocarpaceae are similar in function, though not in development, to those of the Taxaceae, being berry-like with the scales modified, evolved to attract birds into dispersing the seeds. In most of the genera, two to ten or more scales are fused together into a swollen, brightly coloured, edible fleshy aril.
Only one or two scales at the apex of the cone are fertile, each bearing a single wingless seed, but in Saxegothaea several scales may be fertile. The fleshy scale complex is 0.5–3 cm long, the seeds 4–10 mm long. In some genera, the scales are minute and not fleshy, but the seed coat develops a fleshy layer instead, the cone having the appearance of one to three small plums on a central stem; the seeds have a hard coat evolved to resist digestion in the bird's stomach. Members of the cypress family differ in that the bract and seed scales are fused, with the bract visible as no more than a small lump or spine on the scale; the botanical term galbulus is sometimes used instead of strobilus for members of this family. The female cones have one to 20 ovules on each scale, they have peltate scales, as opposed to the imbricate cones described above, though some have imbricate scales. The cones are small, 0.3–6 cm or 1⁄8–2 3⁄8 inches long, spherical or nearly so, like those of Nootka cypress, while others, such as western redcedar and California incense-cedar, are narrow.
The scales are arranged either spirally, or in decussate whorls of two or three four. The genera with spiral scale arrangement were treated in a separate family in the past. In most of the genera, the cones are woody and the seeds have two narrow wings, but in three genera, the seeds are wingless, in Juniperus, the cones are fleshy and
The Triassic is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.9 million years ago, to the beginning of the Jurassic Period 201.3 Mya. The Triassic is the shortest period of the Mesozoic Era. Both the start and end of the period are marked by major extinction events. Triassic began in the wake of the Permian–Triassic extinction event, which left the Earth's biosphere impoverished. Therapsids and archosaurs were the chief terrestrial vertebrates during this time. A specialized subgroup of archosaurs, called dinosaurs, first appeared in the Late Triassic but did not become dominant until the succeeding Jurassic Period; the first true mammals, themselves a specialized subgroup of therapsids evolved during this period, as well as the first flying vertebrates, the pterosaurs, like the dinosaurs, were a specialized subgroup of archosaurs. The vast supercontinent of Pangaea existed until the mid-Triassic, after which it began to rift into two separate landmasses, Laurasia to the north and Gondwana to the south.
The global climate during the Triassic was hot and dry, with deserts spanning much of Pangaea's interior. However, the climate became more humid as Pangaea began to drift apart; the end of the period was marked by yet another major mass extinction, the Triassic–Jurassic extinction event, that wiped out many groups and allowed dinosaurs to assume dominance in the Jurassic. The Triassic was named in 1834 by Friedrich von Alberti, after the three distinct rock layers that are found throughout Germany and northwestern Europe—red beds, capped by marine limestone, followed by a series of terrestrial mud- and sandstones—called the "Trias"; the Triassic is separated into Early and Late Triassic Epochs, the corresponding rocks are referred to as Lower, Middle, or Upper Triassic. The faunal stages from the youngest to oldest are: During the Triassic all the Earth's land mass was concentrated into a single supercontinent centered more or less on the equator and spanning from pole to pole, called Pangaea.
From the east, along the equator, the Tethys sea penetrated Pangaea, causing the Paleo-Tethys Ocean to be closed. In the mid-Triassic a similar sea penetrated along the equator from the west; the remaining shores were surrounded by the world-ocean known as Panthalassa. All the deep-ocean sediments laid down during the Triassic have disappeared through subduction of oceanic plates; the supercontinent Pangaea was rifting during the Triassic—especially late in that period—but had not yet separated. The first nonmarine sediments in the rift that marks the initial break-up of Pangaea, which separated New Jersey from Morocco, are of Late Triassic age. S. these thick sediments comprise the Newark Group. Because a super-continental mass has less shoreline compared to one broken up, Triassic marine deposits are globally rare, despite their prominence in Western Europe, where the Triassic was first studied. In North America, for example, marine deposits are limited to a few exposures in the west, thus Triassic stratigraphy is based on organisms that lived in lagoons and hypersaline environments, such as Estheria crustaceans.
At the beginning of the Mesozoic Era, Africa was joined with Earth's other continents in Pangaea. Africa shared the supercontinent's uniform fauna, dominated by theropods and primitive ornithischians by the close of the Triassic period. Late Triassic fossils are more common in the south than north; the time boundary separating the Permian and Triassic marks the advent of an extinction event with global impact, although African strata from this time period have not been studied. During the Triassic peneplains are thought to have formed in what is now southern Sweden. Remnants of this peneplain can be traced as a tilted summit accordance in the Swedish West Coast. In northern Norway Triassic peneplains may have been buried in sediments to be re-exposed as coastal plains called strandflats. Dating of illite clay from a strandflat of Bømlo, southern Norway, have shown that landscape there became weathered in Late Triassic times with the landscape also being shaped during that time. At Paleorrota geopark, located in Rio Grande do Sul, the Santa Maria Formation and Caturrita Formations are exposed.
In these formations, one of the earliest dinosaurs, Staurikosaurus, as well as the mammal ancestors Brasilitherium and Brasilodon have been discovered. The Triassic continental interior climate was hot and dry, so that typical deposits are red bed sandstones and evaporites. There is no evidence of glaciation near either pole. Pangaea's large size limited the moderating effect of the global ocean; the strong contrast between the Pangea supercontinent and the global ocean triggered intense cross-equatorial monsoons. The Triassic may have been a dry period, but evidence exists that it was punctuated by several episodes of increased rainfall in tropical and subtropical latitudes of the Tethys Sea and its surrounding land. Sediments and fossils suggestive of a more humid climate are known from the Anisian to Ladinian of the Tethysian domain, from the Carnian and Rhaetian of a larger area that includes the Boreal domain, the North
The Permian is a geologic period and system which spans 47 million years from the end of the Carboniferous Period 298.9 million years ago, to the beginning of the Triassic period 251.902 Mya. It is the last period of the Paleozoic era; the concept of the Permian was introduced in 1841 by geologist Sir Roderick Murchison, who named it after the city of Perm. The Permian witnessed the diversification of the early amniotes into the ancestral groups of the mammals, turtles and archosaurs; the world at the time was dominated by two continents known as Pangaea and Siberia, surrounded by a global ocean called Panthalassa. The Carboniferous rainforest collapse left behind vast regions of desert within the continental interior. Amniotes, who could better cope with these drier conditions, rose to dominance in place of their amphibian ancestors; the Permian ended with the Permian–Triassic extinction event, the largest mass extinction in Earth's history, in which nearly 96% of marine species and 70% of terrestrial species died out.
It would take well into the Triassic for life to recover from this catastrophe. Recovery from the Permian–Triassic extinction event was protracted; the term "Permian" was introduced into geology in 1841 by Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Édouard de Verneuil; the region now lies in the Perm Krai of Russia. Official ICS 2017 subdivisions of the Permian System from most recent to most ancient rock layers are: Lopingian epoch Changhsingian Wuchiapingian Others: Waiitian Makabewan Ochoan Guadalupian epoch Capitanian stage Wordian stage Roadian stage Others: Kazanian or Maokovian Braxtonian stage Cisuralian epoch Kungurian stage Artinskian stage Sakmarian stage Asselian stage Others: Telfordian Mangapirian Sea levels in the Permian remained low, near-shore environments were reduced as all major landmasses collected into a single continent—Pangaea; this could have in part caused the widespread extinctions of marine species at the end of the period by reducing shallow coastal areas preferred by many marine organisms.
During the Permian, all the Earth's major landmasses were collected into a single supercontinent known as Pangaea. Pangaea straddled the equator and extended toward the poles, with a corresponding effect on ocean currents in the single great ocean, the Paleo-Tethys Ocean, a large ocean that existed between Asia and Gondwana; the Cimmeria continent rifted away from Gondwana and drifted north to Laurasia, causing the Paleo-Tethys Ocean to shrink. A new ocean was growing on its southern end, the Tethys Ocean, an ocean that would dominate much of the Mesozoic era. Large continental landmass interiors experience climates with extreme variations of heat and cold and monsoon conditions with seasonal rainfall patterns. Deserts seem to have been widespread on Pangaea; such dry conditions favored gymnosperms, plants with seeds enclosed in a protective cover, over plants such as ferns that disperse spores in a wetter environment. The first modern trees appeared in the Permian. Three general areas are noted for their extensive Permian deposits—the Ural Mountains and the southwest of North America, including the Texas red beds.
The Permian Basin in the U. S. states of Texas and New Mexico is so named because it has one of the thickest deposits of Permian rocks in the world. The climate in the Permian was quite varied. At the start of the Permian, the Earth was still in an ice age. Glaciers receded around the mid-Permian period as the climate warmed, drying the continent's interiors. In the late Permian period, the drying continued although the temperature cycled between warm and cool cycles. Permian marine deposits are rich in fossil mollusks and brachiopods. Fossilized shells of two kinds of invertebrates are used to identify Permian strata and correlate them between sites: fusulinids, a kind of shelled amoeba-like protist, one of the foraminiferans, ammonoids, shelled cephalopods that are distant relatives of the modern nautilus. By the close of the Permian, trilobites and a host of other marine groups became extinct. Terrestrial life in the Permian included diverse plants, fungi and various types of tetrapods; the period saw a massive desert covering the interior of Pangaea.
The warm zone spread in the northern hemisphere. The rocks formed at that time were stained red by iron oxides, the result of intense heating by the sun of a surface devoid of vegetation cover. A number of older types of plants and animals became marginal elements; the Permian began with the Carboniferous flora still flourishing. About the middle of the Permian a major transition in vegetation began; the swamp-loving
The Cambrian Period was the first geological period of the Paleozoic Era, of the Phanerozoic Eon. The Cambrian lasted 55.6 million years from the end of the preceding Ediacaran Period 541 million years ago to the beginning of the Ordovician Period 485.4 mya. Its subdivisions, its base, are somewhat in flux; the period was established by Adam Sedgwick, who named it after Cambria, the Latin name of Wales, where Britain's Cambrian rocks are best exposed. The Cambrian is unique in its unusually high proportion of lagerstätte sedimentary deposits, sites of exceptional preservation where "soft" parts of organisms are preserved as well as their more resistant shells; as a result, our understanding of the Cambrian biology surpasses that of some periods. The Cambrian marked a profound change in life on Earth. Complex, multicellular organisms became more common in the millions of years preceding the Cambrian, but it was not until this period that mineralized—hence fossilized—organisms became common; the rapid diversification of life forms in the Cambrian, known as the Cambrian explosion, produced the first representatives of all modern animal phyla.
Phylogenetic analysis has supported the view that during the Cambrian radiation, metazoa evolved monophyletically from a single common ancestor: flagellated colonial protists similar to modern choanoflagellates. Although diverse life forms prospered in the oceans, the land is thought to have been comparatively barren—with nothing more complex than a microbial soil crust and a few molluscs that emerged to browse on the microbial biofilm. Most of the continents were dry and rocky due to a lack of vegetation. Shallow seas flanked the margins of several continents created during the breakup of the supercontinent Pannotia; the seas were warm, polar ice was absent for much of the period. Despite the long recognition of its distinction from younger Ordovician rocks and older Precambrian rocks, it was not until 1994 that the Cambrian system/period was internationally ratified; the base of the Cambrian lies atop a complex assemblage of trace fossils known as the Treptichnus pedum assemblage. The use of Treptichnus pedum, a reference ichnofossil to mark the lower boundary of the Cambrian, is difficult since the occurrence of similar trace fossils belonging to the Treptichnids group are found well below the T. pedum in Namibia and Newfoundland, in the western USA.
The stratigraphic range of T. pedum overlaps the range of the Ediacaran fossils in Namibia, in Spain. The Cambrian Period was followed by the Ordovician Period; the Cambrian is divided into ten ages. Only three series and six stages are named and have a GSSP; because the international stratigraphic subdivision is not yet complete, many local subdivisions are still used. In some of these subdivisions the Cambrian is divided into three series with locally differing names – the Early Cambrian, Middle Cambrian and Furongian. Rocks of these epochs are referred to as belonging to Upper Cambrian. Trilobite zones allow biostratigraphic correlation in the Cambrian; each of the local series is divided into several stages. The Cambrian is divided into several regional faunal stages of which the Russian-Kazakhian system is most used in international parlance: *Most Russian paleontologists define the lower boundary of the Cambrian at the base of the Tommotian Stage, characterized by diversification and global distribution of organisms with mineral skeletons and the appearance of the first Archaeocyath bioherms.
The International Commission on Stratigraphy list the Cambrian period as beginning at 541 million years ago and ending at 485.4 million years ago. The lower boundary of the Cambrian was held to represent the first appearance of complex life, represented by trilobites; the recognition of small shelly fossils before the first trilobites, Ediacara biota earlier, led to calls for a more defined base to the Cambrian period. After decades of careful consideration, a continuous sedimentary sequence at Fortune Head, Newfoundland was settled upon as a formal base of the Cambrian period, to be correlated worldwide by the earliest appearance of Treptichnus pedum. Discovery of this fossil a few metres below the GSSP led to the refinement of this statement, it is the T. pedum ichnofossil assemblage, now formally used to correlate the base of the Cambrian. This formal designation allowed radiometric dates to be obtained from samples across the globe that corresponded to the base of the Cambrian. Early dates of 570 million years ago gained favour, though the methods used to obtain this number are now considered to be unsuitable and inaccurate.
A more precise date using modern radiometric dating yield a date of 541 ± 0.3 million years ago. The ash horizon in Oman from which this date was recovered corresponds to a marked fall in the abundance of carbon-13 that correlates to equivalent excursions elsewhere in the world, to the disappearance of distinctive Ediacaran fossils. There are arguments that the dated horizon in Oman does not correspond to the Ediacaran-Cambrian boundary, but represents a facies change from marine to evaporite-dominated strata — which w