The complex of data recorded in fossils worldwide—known as the fossil record —is the primary source of information about the history of life on Earth. The insect fossil record has many gaps. Among the primitive apterygotes, only the collembolans springtails have been found as fossil s in the Devonian Period about Ten insect orders are known as fossil s, mostly of Late Carboniferous…. Only a small fraction of ancient organisms are preserved as fossils, and usually only organisms that have a solid and resistant skeleton are readily preserved.
Most major groups of invertebrate animals have nudist dating tumblr calcareous skeleton or shell e. Other forms have shells of calcium phosphate which also occurs in the bones of vertebratesor silicon dioxide. A shell or bone that is buried quickly after deposition may retain these organic tissues, though they become who is taylor kinney currently dating converted to a stony substance over time.
Unaltered hard parts, such as the shells of clams or brachiopods, are relatively common in sedimentary rockssome of great age. The hard parts of organisms that become buried in sediment may be subject to a variety of other changes during their conversion to solid rockhowever.
Solutions may fill the interstices, or pores, of the shell or bone with calcium carbonate or other mineral salts and thus fossilize the remains, in a process known as permineralization.
In other cases there may be a total replacement of the original skeletal material by other mineral matter, a process known as mineralization, or replacement.
In still other cases, circulating acid solutions may dissolve the original shell but leave a cavity corresponding to it, and circulating calcareous or siliceous solutions may then deposit a new matrix in the cavity, thus creating a new impression of the original shell. By contrast, the soft parts of animals or plants are very rarely preserved. The embedding of insects in amber a process called resin fossilization dating ariana grande simulator the preservation of the carcasses of Pleistocene mammoths in ice are rare but striking examples of the fossil preservation of soft tissues.
Leavesstemsand other vegetable matter may be preserved through the process of carbonization, where such parts are flattened between two layers of rock. The chemical reduction of the part produces a carbon film that occurs on one layer of rock, while an impression of that part occurs on the other layer of the rock.
Fossils of hard and soft parts that are too small to be observed by the naked eye are called microfossils. The great majority of fossils are preserved in a water environment because land remains are more easily destroyed.
Anaerobic conditions at the bottom of the seas or other bodies of water are especially favourable mountain top dating commercial preserving fine details, since no bottom faunas, except for anaerobic bacteria, are present to destroy the remains. In general, for an organism to be preserved two conditions must be met: In some places, such as the Grand Canyon in northern Arizona, one can observe a great thickness of nearly horizontal strata representing the deposition of sediment on the seafloor over many hundreds of millions of years.
It is often apparent that each layer in such a sequence contains fossils that are distinct from those of the layers that are above and below it. In such sequences of layers in different geographic locations, the same, or similar, fossil floras or faunas occur in the identical order.
By comparing overlapping sequences, it is possible to build up a continuous record of faunas and floras that have progressively more in common with present-day life forms as the top of the sequence is approached. The study of the fossil record has provided important information for at least four different purposes.
The progressive changes observed within an animal group are used to describe the evolution of that group. Fossils also provide the geologist a quick and easy way of assigning a relative age to the strata in which they occur. The precision with which this may be done in any particular case depends on the nature and abundance of the fauna: Fossils used to identify geologic relationships are known as index fossils.
Fossil organisms may provide information about the climate and environment of the site where they were deposited and preserved e. Fossils are useful in the exploration for minerals and mineral fuels. For example, they serve to indicate the stratigraphic position of coal seams. In recent years, geologists have been able to study the subsurface stratigraphy of oil and natural gas deposits by analyzing microfossils obtained from core samples of deep borings.
Fossil collection as performed by paleontologists, geologists, and other scientists typically involves a rigorous excavation and documentation process, mountain top dating commercial.
Unearthing the specimen from the rock is often painstaking work that includes labeling each part of the specimen and cataloging the location of each part within the rock. Those fossils slated for removal from the rock are slowly and carefully excavated using techniques designed to prevent or minimize damage to the specimen. Such fossils often become part of museum or university collections.
Many other fossils, however, are collected by hobbyists and commercial entities. Often such specimens are not carefully documented or excavated, resulting in a loss of data from the site and risking potential damage to the specimen.
For these reasons and the fact that it stimulates nonscientific collecting, the commercial exploitation of fossils is controversial among academic paleontologists.
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The Editors of Encyclopaedia Britannica. May 11, See Article History. Learn More in these related Britannica articles: Among the primitive apterygotes, only the collembolans springtails have been found as fossils in the Devonian Period about Ten insect orders are known as fossils, mostly of Late Carboniferous….
Using fossils simply for identification purposes, Smith constructed a map of the various surface rocks outcropping throughout England, Wales, and southern Scotland.
With rare exceptions, fossils occur only in sedimentary strata. Paleontology, which is the science of ancient life and deals with fossils, is mutually interdependent with stratigraphy and with historical geology.
Paleontology also may be considered to be a branch of biology. Certainly, the trove of fossils from Africa and Eurasia indicates that, unlike today, more than one species of our family has lived at the same time for most of human history.
The nature of specific fossil specimens and species can be accurately described,…. Diatomite contains approximately 3, diatom frustules per cubic millimetre 50 million diatom frustules per cubic inch. When geologic uplifting brings deposits of diatomite above sea level, the diatomite is easily mined. A deposit located in Lompoc, California, U. Ecological and commercial importance aquatic ecosystems In marine ecosystem: Origins of marine life dolomitization In dolomitization fossil record In fossil record human evolution In human evolution insects In insect: Insect fossil record sedimentary strata In geology: Paleontology geochronology In dating: Principles and techniques In Cambrian Period: Articles from Britannica Encyclopedias best thai dating sites elementary and high school students.
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Pacific mountain system , series of mountain ranges that stretches along the Pacific Ocean coast of North America from northern British Columbia Canada to northwestern Mexico. They run for some 4, miles 7, km in the United States and extend northward into Canada for another 1, miles 1, km.
The ranges may be divided into eight sections. In addition, the Sierra Nevada range, in eastern California, is often considered to be part of this system. In general, the movement of tectonic plates has been responsible for the development of the Pacific mountain system.
The coastal mountains from the Queen Charlotte Islands southward to southern California have been folded, faulted, and intruded with molten rock as a result of this movement. The most significant activity has been the lateral, northerly movement of the Pacific Plate west relative to the North American Plate east along transform faults.
Subduction crustal sinking is not currently occurring in these two areas. Seismic activity, particularly in California, is considerable along the transform faults. After Alaska , California is the most earthquake-prone area in North America.
The molten mantle rock produced by this subduction is responsible for the major volcanoes in the Cascade Range. All the Cascade composite cones are of the explosive type, their molten rock being high in silica. Until the eruption of Mount St. Helens in southwestern Washington , Lassen Peak in northern California had been the most recently active volcano —17 in the 48 conterminous U.
Helens eruption, which blew off the top of its cone, was of greater magnitude than any other eruption in the region since the eruption and collapse of Mount Mazama 6, years ago, which formed the caldera now occupied by Crater Lake.
Because the subduction process is not continuous—it is impeded as huge quantities of materials accumulate on plate boundaries—enormous stresses develop. The release of these stresses can create shock waves of a larger magnitude than any other known earthquakes. It is thought that for the past 4, years such subduction-related earthquakes have occurred at intervals of to 1, years. The arrangement of the ranges in the system can be visualized as being in the shape of an extremely elongated H with a closed base.
The Klamath Mountains of southern Oregon and northern California make up the east-west cross in the centre of the H, while the Transverse Ranges bend eastward from the California Coast Ranges to form the closed base of the H. Coastal plains are either narrow or nonexistent along the entire north-south extent of the coastal ranges.
Offshore a narrow continental shelf drops abruptly into ocean depths. In places, waves have cut notches and terraces as the land has risen episodically. More-resistant igneous rocks stand as sea cliffs with undercut notches. Softer sedimentary rocks have been eroded to form embayments.
There is evidence for the periodic rise and fall of the coast as a result of tectonic activity. Stream valleys have been deepened by glaciers to produce a fjordlike coast, with relatively short streams draining the interior. Southward, across the Juan de Fuca Strait , the Olympic Mountains rise to almost 8, feet 2, metres. The highest and most spectacular of the Coast Ranges, they consist of folded sedimentary and metamorphic rock and also have been heavily glaciated.
Drainage is radial from the highest peaks; among the major streams are the Hoh, Quinault, and Elwha. These northern ranges consist of a dissected upland of late Paleozoic rock i. Ridges in the North Cascades rise to elevations between 6, and 8, feet 1, to 2, metres ; above these ridges stand the composite volcanic cones of Glacier Peak and Mount Baker. The Coast Mountains of British Columbia are considerably lower, with the highest elevations reaching 3, to 4, feet to 1, metres in the south.
The higher peaks, however, often are glacier-covered. All the ranges have been heavily dissected by running water both before and after the Pleistocene Epoch about 2,, to 11, years ago. During the Pleistocene they were covered by a cordilleran ice sheet, the glaciers of which occupied and deepened many existing stream valleys. On the east side of the North Cascades, Lake Chelan is in a glacially formed valley, and its deepest points are more than 1, feet metres below the surface.
In the Coast Mountains glacial action has produced a spectacular fjorded coast. Farther south in southern British Columbia and Washington are deep glacial valleys opening out onto the Fraser River delta and the Puget Sound Lowland.
The Middle Cascades, which extend southward from west-central Washington into Oregon, are an uplifted and faulted region consisting of volcanics from the Cenozoic Era i. These volcanics consist of successive layers of tuffs, breccias, and mudflows, covered by basaltic flows. The range can be divided into eastern and western sections, the western being the oldest.
Capping the higher, eastern part of the range is a more recent layer of Cenozoic andesites and basalts. Elevations reach 4, to 6, feet 1, to 1, metres , with a number of volcanic peaks—such as Mounts Rainier and Hood —standing high above the general surface relief. The Columbia River cuts through the Middle Cascades in a magnificent gorge. On the southern Oregon side are numerous hanging valleys with streams that plunge in spectacular waterfalls into the gorge.
About 12, to 10, years ago, a large lake Lake Missoula was impounded by an ice dam in western Montana. On several occasions the dam gave way and released enormous quantities of water, which then rapidly drained to the sea. Those floods deepened and widened the existing Columbia River valley and were largely responsible for the present profile of the gorge. The South Cascades, extending from southern Oregon into northern California, differ from the Middle Cascades in that they were not uplifted.
The Pit River provides a low-elevation passage across these mountains. The Klamath Mountains are the oldest of the Pacific coastal mountains, dating to the early Paleozoic Era i.
They are extremely complex, probably resulting from the collision of tectonic plates in the early Triassic Period about million to million years ago. Later they were intruded by granite batholiths. The Klamath Mountains have been glaciated in their higher elevations and have been heavily dissected by streams; the major watercourse crossing them is the Rogue River.
Both the Coast and the Transverse ranges were formed by plate collisions. The Washington and Oregon Coast Ranges consist of folded gray mudstones and siltstones oriented in a north-south direction.
The major streams are antecedent to the uplift and have been drowned in their lower courses, producing estuaries. In addition to the Columbia, these include the Umpqua and Siuslaw rivers. The California Coast Ranges also are made up of folded and faulted sedimentary rocks. The major faults trend northwest-southeast, however, and the rivers tend to follow these lines of weakness.
The San Andreas Fault , passing through the southern California ranges, more or less bisects them before heading offshore near San Francisco. The eastern section of the Transverse Ranges consists of granites and metamorphic rocks, while the western portion resembles the sedimentary structure of the Coast Ranges; streams draining them include the Santa Clara and Santa Ana rivers.
In the Pacific mountain system are found 10 of the 12 orders of soils, of which 4 are most abundant. They have weakly differentiated horizons layers , are little altered from their parent material, and occur where summers are cool.
Much of the Klamath Mountains area is characterized by ultisols , leached reddish soils that develop where winters are mild and moist and summers are warm and dry. Spodosols form under coniferous forests at higher, cooler elevations.
The orientation of the Pacific mountains has a profound effect on the climate of the western United States and Canada. Regionally, they act as an orographic barrier to storms from the Pacific Ocean, which especially in winter bring large quantities of precipitation to the western slopes of the ranges. For example, the highest annual precipitation levels in the 48 conterminous states more than inches [3, mm] occur on the southwestern slope of the Olympic Mountains, while the greatest annual precipitation total in Canada more than inches [5, mm] occurs along the British Columbia coast north of Vancouver Island.
Inland precipitation decreases on the eastern rain shadow side of the coastal ranges and increases again on the higher, western slopes of the Cascades, in some places exceeding inches 2, mm ; much of this is in the form of snow. Immediately east of the Cascades the annual precipitation decreases drastically to less than 8 inches mm at Yakima, Washington.
In California more than 50 inches 1, mm fall on the windward side of the Coast Ranges, decreasing to 30 inches mm in the Transverse Ranges to the east. In sum, precipitation in these ranges increases with elevation and reaches higher annual levels on the western windward sides. Climate is the major influence on vegetation type. Conifers predominate and can grow to enormous size, especially on the moister, western slopes. Sitka spruces are dominant along the coast from southern British Columbia to northern California.
The largest standing midlatitude rainforest in the United States is on the west side of the Olympic Mountains.
Inland and up into the Cascades, Douglas firs and western hemlocks dominate. They give way at high elevations to trees such as Pacific silver firs and mountain hemlocks. On the eastern slopes of the Cascades, ponderosa pines are the major trees, because they are capable of thriving on the drier slopes where fire is not uncommon.
Along the coast from southern Oregon to the Monterey Peninsula of California, redwoods are dominant, occurring with Sitka spruces, Douglas firs, and hardwoods such as alders. Farther from the coast, the Coast Ranges are characterized by mixed forests of bigleaf maples, madrones, various oaks, and pines and other conifers. On the eastern slopes is an oak-grassland association. In the drier Transverse Ranges, bigcone Douglas firs, as well as pines and oaks, are found.
The anadromous river-spawning salmon are the most distinctive creatures of the coastal ranges. Five species—pink, chum, coho, sockeye, and chinook—are found in the streams draining the mountains, each with its own distinctive range and environmental conditions. The pink and chum spawn in coastal streams near the ocean, while the sockeye usually spawns in upstream lakes.
The chinook or king favours large rivers such as the Columbia and Sacramento and travels hundreds of miles inland. The coho also favours the larger rivers. Another anadromous fish, the American shad, originally native to the Atlantic coast, was introduced in the late 19th century and has adapted to streams of the Pacific coast.
Also inhabiting coastal waters are harbour seals, northern fur seals, northern elephant seals, sea otters, and northern and California sea lions. The pelts of sea otters were the first furs traded in the Pacific coastal region, obtained from the Indians of British Columbia and sold in China. The larger land mammals include Roosevelt elk in the coastal ranges from British Columbia to northern California and black bears in the coastal ranges and Cascades. Three species of deer are found: Three members of the cat family—lynx, bobcat, and puma mountain lion —are found throughout the Pacific mountain system.
The beaver, a mainstay of the 18th- and 19th-century fur trade, is found as far south as northern California. Brought to the brink of extinction in the 19th century, beavers are now protected in most areas.
The Pacific mountain region had a large American Indian population before the arrival of white explorers and settlers.
Rocky Mountain has a large selection of Antique and Vintage American Quilt Tops, Blocks and Feedsacks for Sale. Pacific mountain system: Pacific mountain system, series of mountain ranges that stretches along the Pacific Ocean coast of North America from northern British Columbia (Canada) to northwestern Mexico. Fossil: Fossil, remnant, impression, or trace of an animal or plant of a past geologic age that has been preserved in Earth’s crust. The complex of data recorded in fossils worldwide—known as the fossil record—is the primary source of information about the history of life on Earth.
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