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Pliocene

Pliocene

The Pliocene epoch (formerly Pleiocene) is the period in the geologic timescale that extends from 5.3 million to 1.8 million years before present. The Pliocene follows the Miocene epoch and is followed by the Pleistocene epoch. The Pliocene is the second epoch of the Neogene period. As with other older geologic periods, the rock beds that define the start and end are well identified, but the exact dates of the start and end of the epoch are slightly uncertain. The Pliocene was named by Sir Charles Lyell. The name comes from the Greek words pleion (more) and ceno (new) and means roughly "continuation of the recent" and refers to the essentially modern mammalian faunas. The Pliocene boundaries are not set at an easily identified worldwide event but rather at regional boundaries between the warmer Miocene and the relatively cooler Pliocene. The upper boundary was intended to be set at the start of the Pleistocene glaciations but is now considered to be set too late.

Pliocene subdivisions

The Pliocene faunal stages from youngest to oldest are:

Pliocene climate

Climates became cooler and drier, and seasonal, similar to modern climates. Antarctica became ice-bound, entirely covered with year-round glaciation, near or before the start of the Pliocene. The formation of an Arctic ice cap ca 3 mya is signalled by an abrupt shift in oxygen isotope ratios and ice-rafted cobbles in the North Atlantic and North Pacific ocean beds (Van Andel 1994 p 226). Mid-latitude glaciation were probably underway before the end of the epoch.

Pliocene paleogeography

Continents continued to drift toward their present positions, moving from positions possibly as far as 250km from their present locations to positions only 70 km from their current locations. South America became linked to North America through the Isthmus of Panama during the Pliocene, bringing a nearly complete end to South America's distinctive marsupial faunas. The formation of the Isthmus would have major consequences on global temperatures, as warm equatorial ocean currents were cut off and an Atlantic cooling cycle began, with cold Arctic and Antarctic waters dropping temperatures in the now-isolated Atlantic Ocean. Africa's collision with Europe formed the Mediterranean Sea, cutting off the remnants of the Tethys Ocean. Sea level changes exposed the land-bridge between Alaska and Asia. Pliocene marine rocks are well exposed in the Mediterranean, India, and China. Elsewhere, they are exposed largely near shores.

Pliocene flora

The change to a cooler, dry, seasonal climate had considerable impacts on pliocene vegetation, reducing tropical species world-wide. Deciduous forests proliferated, coniferous forests and tundra covered much of the north, and grasslands spread on all continents (except Antarctica). Tropical forests were limited to a tight band around the equator, and in addition to dry savannahs, deserts appeared in Asia and Africa.

Pliocene fauna

Both marine and continental faunas were essentially modern, although continental faunas were recognizably a bit more primitive than today. The first recognizable hominins, the australopithecines, appeared in the Pliocene. The land mass collisions meant great migration and mixing of previously isolated species. Herbivores got bigger, as did specialized predators.

Mammals

In North America, rodents, large mastodonts and gomphotheres, and opossums continued successfully, while hoofed animals (ungulates) declined, with camel, deer and horse all seeing populations recede. Rhinos, tapirs and chalicotheres went extinct. Carnivores including the weasel family diversifed, and dogs and fast-running hunting bears did well. Ground sloths, huge glyptodonts and armadillos came north with the formation of the Panamanian Isthmus. In Eurasia rodents did well, while primate coverage declined. Elephants, gomphotheres and stegodonts were successful in Asia, and hyraxes migrated north from Africa. Horse diversity declined, while tapirs and rhinos did fairly well. Cows and antelopes were successful, and some camel species crossed into Asia from North America. Hyaenas and early saber-toothed cats appeared, joining other predators including dogs, bears and weasels. Africa was dominated by hoofed animals, and primates continued their evolution, with australopithecines (some of the first hominids) appearing in the late Pliocene. Rodents were successful, and elephant populations increased. Cows and antelopes continued diversification and overtaking pigs in numbers of species. Early giraffes appeared, and camels migrated via Asia from North America. Horses and modern rhinos came onto the scene. Bears, dogs and weasels (originally from North America) joined cats, hyaenas and civets as the African predators, forcing hyaenas to adapt as specialized scavengers. South America was invaded by North American species for the first time since the Cretaceous, with North American rodents and primates mixing with Southern forms. Litopterns and the notoungulates, South American natives, did well. Small weasel-like mustelids and coatis, carnivores both, migrated from the north. Grazing glyptodonts, browsing giant ground sloths and smaller armadillos did well. The marsupials remained the dominant Australian mammals, with herbivore forms including wombats and kangaroos, and the huge diprotodonts. Carnivorous marsupials continued hunting in the Pliocene, including dasyurids, the dog-like thylacine and cat-like Thylacoleo. The first rodents arrived, while bats did well, as did ocean-going whales. The modern duck-billed platypus, a monotreme, appeared.

Birds

Pliocene oceans

Oceans continued to be relatively warm during the Pliocene, though continued cooling. The Arctic ice cap formed, drying the climate and increasing cool shallow currents in the North Atlantic. Deep cold currents flowed from the Antarctic. The formation of the Isthmus of Panama about 3.5 million years ago cut off the final remnant of what was once essentially a circum-equatorial current that existed during the Cretaceous and the early Cenozoic. This may have contributed to further cooling of the oceans worldwide. The Pliocene seas were alive with sea cows, seals and sea lions.

See also


- Geologic Time Scale

Further reading


- Van Andel, Tjeerd H., New Views on an Old Planet: a History of Global Change (2nd edition, 1994)

External links


- [http://www.bbc.co.uk/beasts/changing/pliocene/index.shtml BBC Changing Worlds: Pliocene]
- [http://www.palaeos.com/Cenozoic/Pliocene/Pliocene.htm Palaeos Pliocene]
- [http://www.pbs.org/wgbh/evolution/change/deeptime/pliocene.html PBS Change: Deep Time: Pliocene]
- [http://www.ucmp.berkeley.edu/tertiary/pli.html UCMP Berkeley Pliocene Epoch Page]
- [http://www.giss.nasa.gov/research/features/pliocene/ Mid-Pliocene Global Warming: NASA/GISS Climate Modeling] ja:鮮新世

Epoch

The word epoch can mean either an interval of time, or a particular point in time used as a reference point.
- In common usage, the term is often used to apply to a period of time when significant related events took place. Synonyms include historical period and era (links are to disambiguation pages).
- In geology, the recent (to the geologist) past is divided into a series of epochs of a few million years each. See geologic timescale.
- In computing and telecommunications, an epoch date is a specific date and time used as the reference for all other times. The Unix epoch is an example.
- In astronomy, an epoch (astronomy) is a moment in time for which celestial coordinates or orbital elements are specified.
- The epoch of a calendar era is the year, day, or instant from which the later (and earlier) years of a calendar are counted.
- The Epoch was a vehicle capable of time travel in the popular SNES game, Chrono Trigger.
- Epoch is a supervillian written in DC comics also known as the Lord of Time.
- Epoch is the name of a Japanese video game company. They released consoles in the early and mid 1980s
- [http://www.imdb.com/title/tt0233657/ Epoch] is the name of a TV movie from the year 2000.

Pleiocene

Pliocene

Geologic Timescale

The geologic time scale is used by geologists and other scientists to describe the timing and relationships between events that have occurred during the history of the Earth. The table of geologic periods presented here is in accordance with the dates and nomenclature proposed by the International Commission on Stratigraphy, and uses the standard color codes of the United States Geologic Survey. Geological evidence indicates that Earth is about 4570 million years old. The geologic or "deep" time of Earth's past has been organized into various units according to events which took place in each period. Different spans of time on the time scale are usually delimited by major geologic or paleontologic events, such as mass extinctions. For example, the boundary between the Cretaceous period and the Palaeogene period is defined by the extinction event that marked the demise of the dinosaurs and of many marine species.

Terminology

The largest defined unit of time is the Eon. Eons are divided into Eras, which are in turn divided into Periods, Epochs and Stages. At the same time, paleontologists define a system of faunal stages, of varying lengths, based on changes in the observed fossil assemblages. In many cases, such faunal stages have been adopted in building the geologic nomenclature, though in general there are far more recognized faunal stages than defined geologic time units. Geologists tend to talk in terms of Upper/Late, Lower/Early and Middle parts of periods and other units -- e.g. "Upper Jurassic", "Middle Cambrian". Because geologic units occurring at the same time but from different parts of the world can often look different and contain different fossils, there are many examples where the same period was historically given different names in different locales. For example, in North America the Early Cambrian is refered to as the Waucoban series that is then subdivided into zones based on trilobites. The same timespan is split into Tommotian, Atdabanian and Botomian stages in East Asia and Siberia. It is a key aspect of the work of the International Commission on Stratigraphy to reconcile this conflicting terminology and define universal horizons that can be used around the world.

History of the time scale

The principles underlying geologic time scales were laid down by Nicholas Steno in the late 17th century. Steno argued that rock layers (strata) are laid down in succession, and that each represents a "slice" of time. He also formulated the principle of superposition, which states that any given stratum is probably older than those above it and younger than those below it. Steno's principles were simple; applying them to real rocks proved complex. Over the course of the 18th century geologists came to realize that: 1) Sequences of strata were often eroded, distorted, tilted, or even inverted after deposition; 2) Strata laid down at the same time in different areas could have entirely different appearances; 3) The strata of any given area represented only part of the Earth's long history. The first serious attempts to formulate a geological time scale that could be applied anywhere on Earth took place in the late 18th century. The most influential of those early attempts (championed by Abraham Werner, among others) divided the rocks of the Earth's crust into four types: Primary, Secondary, Tertiary, and Quaternary. Each type of rock, according to the theory, formed during a specific period in Earth history. It was thus possible to speak of a "Tertiary Period" as well as of "Tertiary Rocks." Indeed, "Tertiary" and "Quaternary" remained in use as names of geological periods well into the 20th century. The identification of strata by the fossils they contained, pioneered by William Smith, Georges Cuvier, and Alexandre Brogniart in the early 19th century, enabled geologists to divide Earth history more finely and precisely. It also enabled them to correlate strata across national (or even continental) boundaries. If two strata (however distant in space or different in composition) contained the same fossils, chances were good that they had been laid down at the same time. Detailed studies of the strata and fossils of Europe produced, between 1820 and 1850, the sequence of geological periods still used today. British geologists dominated the process, and the names of the periods reflect that dominance. The "Cambrian," "Ordovician," and "Silurian" periods were named for ancient British tribes (and defined using stratigraphic sequences from Wales). The "Devonian" was named for the British county of Devon, and the name "Carboniferous" was simply an adaptation of "the Coal Measures," the old British geologists' term for the same set of strata. The "Permian," though defined using strata in Russia, was delineated and named by a British geologist: Roderick Murchison. British geologists were also responsible for the grouping of periods into Eras and the subdivision of the Tertiary and Quaternary periods into epochs. When William Smith and Sir Charles Lyell first recognized that rock strata represented successive time periods, there was no way to determine what time scale they represented. Creationists proposed dates of only a few thousand years, while others suggested large (and even infinite) ages. For over 100 years, the age of the Earth and of the rock strata was the subject of considerable debate until advances in the latter part of the 20th century allowed radioactive dating to provide relatively firm dates to geologic horizons. In the intervening century and a half, geologists and paleontologists constructed time scales based solely on the relative positions of different strata and fossils. In 1977, the Global Commission on Stratigraphy (now the International Commission) started an effort to define global references (Global Boundary Stratotype Sections and Points) for geologic periods and faunal stages. Their most recent work is described in the 2004 geologic time scale of Gradstein et al. (ISBN 0521786738), and used as the foundation of this page.

Table of geologic time

# Paleontologists often refer to faunal stages rather than geologic periods. The stage nomenclature is quite complex. See [http://flatpebble.nceas.ucsb.edu/cgi-bin/bridge.pl?action=startScale Harland] for an excellent time ordered list of faunal stages. # Dates are slightly uncertain with differences of a few percent between various sources being common. This is largely due to uncertainties in radiometric dating and the problem that deposits suitable for radiometric dating seldom occur exactly at the places in the geologic column where they would be most useful. The dates and errors quoted above are according to the International Commission on Stratigraphy 2004 time scale. Dates labeled with a
- indicate boundaries where a Global Boundary Stratotype Section and Point has been internationally agreed upon. # Historically, the Cenozoic has been divided up into the Quaternary and Tertiary sub-eras, as well as the Neogene and Paleogene periods. However, the International Commission on Stratigraphy has recently decided to stop endorsing the terms Quaternary and Tertiary as part of the formal nomenclature. # In North America, the Carboniferous is subdivided into Mississippian and Pennsylvanian Periods. # The Proterozoic, Archean and Hadean are often collectively referred to as Precambrian Time, and sometimes also as the Cryptozoic. # Defined by absolute age (Global Standard Stratigraphic Age). # Though commonly used, the Hadean is not a formal eon and no lower bound for the Eoarchean has been agreed upon. The Hadean has also sometimes been called the Priscoan. # These four era names were taken from Moon geology. Their use for Earth geology is unofficial. # The start time for the Holocene epoch is here given as 11,430 years ago ± 130 years. For further discussion of the dating of this epoch, see Holocene.

Graphical timelines

The second and third timelines are each subsections of their preceding timeline as indicated by asterisks.

References


- [http://www.stratigraphy.org/geowhen/ GeoWhen Database ]
- [http://www.stratigraphy.org/gssp.htm International Commission on Stratigraphy Time Scale ]
- [http://www.chronos.org CHRONOS ]
- [http://www.chronos.org/education/educational_resources.html CHRONOS Geologic Time references ]
- [http://www.nmnh.si.edu/paleo/geotime/index.htm Nation Museum on Natural History Geologic Time ]
- [http://www.bbc.co.uk/history/games/rocky/indextime.html BBC Interactive Time Line]

See also


- Age of the Earth
- Fossils and the geological timescale
- Timeline of evolution
- Cosmological timeline
- Lunar geologic timescale
- Martian geologic timescale
- Anthropocene
- Logarithmic timeline

External link


- [http://rst.gsfc.nasa.gov/Sect2/Sect2_1b.html NASA: Geologic Time]
- [http://www.geosociety.org/science/timescale/timescl.htm GSA: Geologic Time Scale] Category:Earth sciences Category:Geology Category:Geochronology ko:지질 시대 ja:地質時代

Pleistocene

The Pleistocene Epoch is part of the geologic timescale. The name of the pleistocene is derived from the Greek pleistos (most) and ceno (new). The Pleistocene follows the Pliocene epoch and is followed by the Holocene epoch. The Pleistocene is the third epoch of the Neogene period or 6th epoch of the Cenozoic era. The end of the Pleistocene corresponds with the end of the Paleolithic age used in archaeology.

Pleistocene dating

The Pleistocene is usually dated from between 1.6-1.9 million to about 10,000 years before present, with the end date expressed in radiocarbon years. It covers most of the latest period of repeated glaciation, up to and including the Younger Dryas cold. The end of the Younger Dryas has been dated to about 9600 BC (11550 calendar years BP). The GSSP for the start of the Pleistocene is in a reference section at Vrica, 4 km south of Crotone in Calabria, southern Italy, that has unresolved dating ambiguities. As with other older geologic periods, the rock beds that define the start of the Pleistocene are well identified, but the exact dates of the start and end of the period are slightly uncertain. The name was intended to cover the recent period of repeated glaciations; however, the start was set too late and some early cooling and glaciation are now known to be in the Pliocene. Some would therefore prefer a start date of around 2.5 million years BP. The name Plio-Pleistocene is in use to mean the last ice age.

Pleistocene paleogeography and climate

rock time.]] The modern continents were essentially at their present positions during the Pleistocene, probably moving no more than 100km.

Glacial features

Pleistocene climate was characterized by repeated glacial cycles where continental glaciers pushed to the 40th parallel in some places. It is estimated that, at maximum glacial extent, 30% of the Earth's surface was covered by ice. In addition, a zone of permafrost stretched southward from the edge of the glacial sheet, a few hundred km in North America, and several hundred in Eurasia. The mean annual temperature at the edge of the ice was -6 deg. C; at the edge of the permafrost, 0 deg. C. Each glacial advance tied up huge volumes of water in continental ice sheets 1500-3000 meters thick, resulting in temporary sea level drops of 100 meters or more over the entire surface of the Earth. During interglacial times, such as we are experiencing now, drowned coastlines were common, mitigated by isostatic or other emergent motion of some regions. The effects of glaciation were global. Antarctica was ice-bound throughout the Pleistocene as well as the preceding Pliocene. The Andes were covered, in the south by the Patagonian ice cap. There were glaciers in New Zealand and Tasmania. The current decaying glaciers of Mount Kenya, Mount Kilimanjaro, Ruwenzori in east and central Africa were larger. Glaciers existed in the mountains Ethiopia and to the west in the Atlas mountains. In the northern hemisphere, many glaciers fused into one. The Cordilleran ice sheet covered the North American northwest; the east was covered by the Laurentide. The Scandinavian ice sheet rested on north Europe, including Britain; the Alpine on the Alps. Scattered domes stretched across Siberia and the Arctic shelf. The northern seas were frozen. South of the ice sheets large lakes accumulated due to blockage of outlets and decreased evaporation in the cooler air. North central North America was totally covered by Lake Agassiz. Over 100 basins, now dry or nearly so, were overflowing in the American west. Lake Bonneville, for example, stood where Great Salt Lake now does. In Eurasia large lakes developed as a result of the runoff from the glaciers. Rivers were larger, had a more copious flow, and were braided. African lakes were fuller, apparently from decreased evaporation. Deserts on the other hand were drier and more extensive. Due to the decrease in oceanic and other evaporation, rainfall was lower.

Major events

Four major glacial events have been identified, as well as many minor intervening events. A major event is a general glacial excursion, termed just a "glacial." Glacials are separated by "interglacials." During a glacial, the glacier experiences minor advances and retreats. The minor excursion is a "stadial"; times between stadials are "interstadials." These events are defined differently in different regions of the glacial range, which have their own glacial history depending on latitude, terrain and climate. There is a general correspondance between glacials in different regions. Investigators often interchange the names if the glacial geology of a region is in the process of being defined. However, it is generally incorrect to apply the name of a glacial in one region to another. You would not refer to the Mindel as the Elsterian or vice versa. For most of the 20th century only a few regions had been studied and the names were relatively few. Today the geologists of different nations are taking more of an interest in Pleistocene glaciology. As a consequence, the number of names is expanding rapidly, and will continue to expand. Four of the better known regions with the names of the glacials are listed in the table below. Fuller information including the dates is stated in the linked articles, which combine the same glaciation of different regions. A synthesis of the larger picture is shown under Timeline of glaciation. It should be emphasized that these glacials are a simplification of a more complex cycle of variation in climate and terrain. Many of the advances and stadials remain unnamed. Also, the terrestrial evidence for some of them has been erased or obscured by larger ones, but we know they existed from the study of cyclical climate changes. Corresponding to the terms glacial and interglacial, the terms pluvial and interpluvial are in use. A pluvial is a warmer period of increased rainfall; an interpluvial, of decreased rainfall. Formerly a pluvial was thought to correspond to a glacial in regions not iced, and in some cases it does. Rainfall is cyclical also. Pluvials and interpluvials are widespread. There is no systematic correspondance of pluvials to glacials, however. Moreover, regional pluvials do not correspond to each other globally. For example, some have used the term "Riss pluvial" in Egyptian contexts. Any coincidence is an accident of regional factors. Names for some pluvials in some regions have been defined.

Palaeocycles

The sum of transient factors acting at the Earth's surface is cyclical: climate, ocean currents and other movements, wind currents, temperature, etc. The waveform response comes from the underlying cyclical motions of the planet, which eventually drag all the transients into harmony with them. The repeated glaciations of the Pleistocene were caused by the same factors.

Milankovitch Cycles

Glaciation in the Pleistocene was a series of glacials and interglacials, stadials and interstadials, mirroring periodic changes in climate. The main factor at work in climate cycling is now believed to be Milankovitch cycles. These are periodic variations in regional solar radiation caused by the sum of a number of repeating changes in the Earth's motion. Milankovitch cycles cannot be the sole factor, as they do not explain the start and end of the Pleistocene ice age, or repeated ice ages. They seem to work best within the Pleistocene, predicting a glaciation once every 100,000 years.

Oxygen Isotope Ratio Cycles

In oxygen isotope ratio analysis, variations in the ratio of O-18 to O-16 (two isotopes of oxygen) by mass (measured by a mass spectrometer) present in the calcite of oceanic core samples is used as a diagnostic of ancient ocean temperature change and therefore of climate change. Cold oceans are richer in O-18, which is included in the shells of the microorganisms contributing the calcite. A more recent version of the sampling process makes use of modern glacial ice cores. Although less rich in O-18 than sea water, the snow that fell on the glacier year by year nevertheless contained O-18 and O-16 in a ratio that depended on the mean annual temperature. Temperature and climate change are cyclical when plotted on a graph of temperature versus time. Temperature coordinates are given in the form of a deviation from today's annual mean temperature, taken as zero. This sort of graph is based on another of isotope ratio versus time. Ratios are converted to a percentage difference (δ) from the ratio found in standard mean ocean water (SMOW). The graph in either form appears as a waveform with overtones. One half of a period is a Marine isotopic stage (MIS). It indicates a glacial (below zero) or an interglacial (above zero). Overtones are stadials or interstadials. According to this evidence, Earth experienced 44 MIS stages beginning at about 2.4 MYA in the Pliocene. Pliocene stages were shallow and frequent. The latest were the most intense and most widely spaced. By convention, stages are numbered from the Holocene, which is MIS1. Glacials receive an even number; interglacials, odd. The first major glacial was MIS22 at about 850,000 YA. The largest glacials were 2, 6 and 12; the warmest interglacials, 1, 5, 9 and 11. For matching of MIS numbers to named stages, see under the articles for those names.

Pleistocene fauna

There are no faunal stages defined for the Pleistocene or Holocene. Both marine and continental faunas were essentially modern. It is believed by most scientists that humans evolved into modern man during the Pleistocene. Major extinctions of large mammals, including mammoths, mastodons, saber-toothed cats, glyptodons and Ground sloths, started late in the Pleistocene and continued into the Holocene. The extinctions were especially severe in North America where native horses and camels were eliminated.

Pleistocene deposits

Pleistocene continental deposits are found primarily in lakebeds, loess deposits and caves as well as in the large amounts of material moved about by glaciers. Pleistocene marine deposits are found primarily in areas within a few tens of kilometers of the modern shoreline. In a few geologically active areas such as the Southern California coast, Pleistocene marine deposits may be found at elevations of several hundred meters.

See also


- Ice age

External links


- [http://www.stratigraphy.org/vrica.htm Vrica] ko:플라이스토세 ja:更新世

Neogene

Neogene Period: A unit of geologic time consisting of the Miocene, Pliocene, Pleistocene, and Holocene epochs. The Neogene Period follows the Paleogene Period. In the past, the terms 'Neogene System' and 'Upper Tertiary System' have been used to describe what is currently called the 'Neogene Period'. At that time, the Neogene ended with the beginning of the Quaternary, i.e. stopped at the Pliocene-Pleistocene boundary. At present, there is a movement amongst geologist (particularly Neogene Marine Geologists) to also include ongoing geological time (Quaternary) in the Neogene, while others (particularly Quaternary Terrestrial Geologists) insist the Quaternary to be a separate Period of distinctly different record. The somewhat confusing terminology and disagreement amongst geologist on where to draw what hierarchical boudaries, is due to the comparatively fine granularity of time units as time approaches the present, and due to geological preservation that causes the youngest sedimentary geological record to be preserved over a much larger area and reflecting much more environments, than the slightly older geological record. By dividing the Cenozoic era into two three (arguably two) 'periods' (Paleogene,Neogene,Quaternary) instead of 7 'epochs', the periods are more closely comparable to the duration of 'periods' in the Mesozoic and Paleozoic eras. The Neogene covers roughly 26 million years. During the Neogene mammals and birds evolved considerably. Most other forms were relatively unchanged. Some continental motion took place, the most significant event being the connection of North and South America in the late Pliocene. Climates cooled somewhat over the duration of the Neogene culminating in continental glaciations in the Quaternary Era that follows, and that saw the dawn of Man. ja:新第三紀

Sir Charles Lyell

Sir Charles Lyell (November 14, 1797 – February 22, 1875), British lawyer, geologist, and popularizer of uniformitarianism. Charles Lyell was born in Kinnordy, Forfarshire, Scotland, the eldest of ten children. Lyell's father, also named Charles, was a botanist of minor repute and first exposed the younger Charles to the study of nature. Having attended Exeter College, Oxford ending in 1816, Lyell encountered geology as a serious profession under the wing of William Buckland. Upon graduation he took a professional detour into the law, but dabbled in geology. His first paper, "On a Recent Formation of Freshwater Limestone in Forfarshire", was presented in 1822. By 1827 he had abandoned the law and embarked on a long geological career that would result in the widespread acceptance of the ideas proposed by James Hutton a few decades before. His most important specific work was in the field of stratigraphy. In 1828, he travelled to the south of France and to Italy, where he realised that the recent strata could be categorised according to the number and proportion of marine shells encased within. Based on this he proposed dividing the Tertiary period into three parts, which he named the Pliocene, Miocene, and Eocene. From 1830 to 1833 his multi-volume Principles of Geology was published. The work's subtitle was "An Attempt to Explain the Former Changes of the Earth's Surface by Reference to Causes now in Operation", and this explains Lyell's impact on science. He was, along with the earlier John Playfair, the major advocate of the then-controversial idea of uniformitarianism, that the earth was shaped entirely by slow-moving forces acting over a very long period of time. This was in contrast to catastrophism, a geologic idea that went hand-in-hand with age of the earth as implied by biblical chronology. In various revised editions (twelve in all, through 1872), Principles of Geology was the most influential geological work in the middle of the 19th century, and did much to put geology on a modern footing. For his efforts he was knighted in 1848, then made a baronet in 1864. During the 1840s, he travelled to the United States and Canada, which resulted in his writing two popular travel-and-geology books: 1845's Travels in North America and A Second Visit to the United States (from 1849). Charles Darwin was a close personal friend, and Lyell was one of the first prominent scientists to support The Origin of Species — though he never fully accepted natural selection as the driving engine behind evolution. In fact, Lyell was instrumental in arranging the peaceful co-publication of the theory of natural selection by Darwin and Alfred Russel Wallace in 1858, after each discovered it independently. Lyell's own The Geological Evidence of the Antiquity of Man followed a few years later in 1863. He won the Copley Medal in 1858 and the Wollaston Medal in 1866. Upon his death in 1875, he was buried in Westminster Abbey. Lyell crater on the Moon and a crater on Mars were named in his honour. Lyell, Charles Lyell, Charles Lyell, Charles Lyell, Charles Lyell, Charles Lyell, Charles

External links


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Mammal



- Subclass Multituberculata (extinct)
  - Plagiaulacida
  - Cimolodonta
- Subclass Palaeoryctoides (extinct)
- Subclass Triconodonta (extinct)
- Subclass Eutheria (includes extinct ancestors)/Placentalia (excludes extinct ancestors)
  - Afrosoricida
  - Artiodactyla
  - Carnivora
  - Cetacea
  - Chiroptera
  - Cimolesta (extinct)
  - Creodonta (extinct)
  - Condylarthra (extinct)
  - Dermoptera
  - Desmostylia (extinct)
  - Embrithopoda (extinct)
  - Hyracoidea
  - Insectivora
  - Lagomorpha
  - Litopterna (extinct)
  - Macroscelidea
  - Mesonychia (extinct)
  - Notoungulata (extinct)
  - Perissodactyla
  - Pholidota
  - Plesiadapiformes (extinct)
  - Primates
  - Proboscidea
  - Rodentia
  - Scandentia
  - Sirenia
  - Taeniodonta (extinct)
  - Tillodontia (extinct)
  - Tubulidentata
  - Xenarthra
- Subclass Marsupialia
  - Dasyuromorphia
  - Didelphimorphia
  - Diprotodontia
  - Microbiotheria
  - Notoryctemorphia
  - Paucituberculata
  - Peramelemorphia
- Subclass Monotremata
  - Monotremata The mammals are the class of vertebrate animals characterized by the presence of mammary glands, which in females produce milk for the nourishment of young; the presence of hair or fur; and which have endothermic or "warm-blooded" bodies. The brain regulates endothermic and circulatory systems, including a four-chambered heart. Mammals encompass some 5500 species, distributed in about 1200 genera, 152 families and up to 46 orders, though this varies depending on the classification scheme adopted. Phylogenetically, Mammalia is defined as all of the descendants of the last common ancestor of monotremes (e.g., echidnas) and therian mammals (placentals and marsupials).

Characteristics

While most mammals give birth to live young, there are a few mammals (the monotremes) that lay eggs. Live birth also occurs in a variety of non-mammalian species, such as guppies and hammerhead sharks; thus it is not a distinguishing characteristic of mammals. Although all mammals are endothermic, so are birds and so this is also not a main defining feature. While monotremes do not have nipples, they do have mammary glands, meaning that they meet all conditions for inclusion in the class Mammalia. It should be noted that the current trend in taxonomy is to emphasize common ancestry; the diagnostic characteristics are useful for identifying this ancestry, but if, for example, a cetacean were found that had no hair at all, it would still be classified as a mammal. Mammals have three bones in each ear and one (the dentary) on each side of the lower jaw; all other vertebrates with ears have one bone (the stapes) in the ear and at least three on each side of the jaw. A group of therapsids called cynodonts had three bones in the jaw, but the main jaw joint was the dentary and the other bones conducted sound. The extra jaw bones of other vertebrates are thought to be homologous with the malleus and incus of the mammal ear. All mammalian brains possess a neocortex. This brain region is unique to mammals. Mammals have integumentary systems made up of three layers: the outermost epidermis, the dermis, and the hypodermis. The epidermis is typically ten to thirty cells thick, its main function being to provide a waterproof layer. Its outermost cells are constantly lost; its bottommost cells are constantly dividing and pushing upward. The middle layer, the dermis, is fifteen to forty times thicker than the epidermis. The dermis is made up of many components such as bony structures and blood vessels. The hypodermis is made up of adipose tissue. Its job is to store lipids, and to provide cushioning and insulation. The thickness of this layer varies widely from species to species. Most mammals are terrestrial, but a number are aquatic, including sirenia (manatees and dugongs) and the cetaceans (dolphins and whales). Whales are the largest of all animals. There are semi-aquatic species such as seals which come to land to breed but spend the majority of the time in water. True flight has evolved only once in mammals, the bats; mammals such as flying squirrels and flying lemurs are actually gliding animals. No mammals have hair naturally blue or green in colour. Some cetaceans, along with the mandrills appear to have shades of blue skin. Many mammals are indicated as having blue hair or fur, but in all cases, it will be found to be a shade of grey. The two-toed sloth can seem to have green fur, however, this colour is caused by algae growths.

Origins

Mammals belong among the amniotes, and in particular to a group called the synapsids, distinguished by the shape of their skulls, in particular the presence of a single hole where jaw muscles attach, called temporal fenestra. In comparison, dinosaurs, birds, and most reptiles are diapsids, with two temporal fenestrae; and turtles, with no temporal fenestra, are anapsids. From synapsids came the first mammal precursors, therapsids, and more specifically the eucynodonts, 220 million years ago (mya) during the Triassic period. Pre-mammalian ears began evolving in the late Permian to early Triassic to their current state, as three tiny bones (incus, malleus, and stapes) inside the skull; accompanied by the transformation of the lower jaw into a single bone. Other animals, including reptiles and pre-mammalian synapsids and therapsids, have several bones in the lower jaw, some of which are used for hearing; and a single ear-bone in the skull, the stapes. This transition is evidence of mammalian evolution from reptilian beginnings: from a single ear bone, and several lower jaw bones (for example the sailback pelycosaur, Dimetrodon) to progressively smaller "hearing jaw bones" (for example the cynodont, Probainognathus), and finally (possibly with Morganucodon, but definitely with Hadrocodium), true mammals with three ear bones in the skull and a single lower jaw bone. Hence pelycosaurs and cynodonts are sometimes called "mammal-like reptiles", though this is strictly incorrect since in modern parlance these two are not reptiles, but rather synapsids. During the Mesozoic Period mammals diversified into four main groups: multituberculates, monotremes, marsupials, and placentals. Multituberculates went extinct during the Oligocene, about 30 million years ago, but the three other mammal groups are all represented today. Most early mammals remained small and shrew-like throughout the Mesozoic, but rapidly developed into larger more diverse forms following the Cretaceous-Tertiary extinction event 65 mya. The names "Prototheria", "Metatheria" and "Eutheria" expressed the theory that Placentalia were descendants of Marsupialia, which were in turn descendants of Monotremata, but this theory has been refuted. However, Eutheria and Metatheria are often used in paleontology, especially with regards to mammals of the Mesozoic. Mammal evolutionary progression is below:
- Jawless fish: Cambrian period to mid Ordovician periods
- Bony fish: mid-Ordovician period to late Devonian period
- Amphibians: late Devonian period to early Carboniferous period
- Reptiles: late Carboniferous period
- Pelycosaurs (synapsids, or "mammal-like reptiles"): late Carboniferous period to very early Triassic period
- Cynodonts: Permian-Triassic
- Mammals: mid-Triassic period to today

In the Mesozoic

Most early mammals were small shrew-like animals that fed on insects. However, in January 2005, the discovery was reported of two fossils of Repenomamus around 130 million years old, one more than a meter in length, the other having remains of a baby dinosaur in its stomach (Nature, Jan. 15, 2005 [http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v433/n7022/full/433116b_fs.html].) The earliest mammals include:
- Eozostrodon: Triassic and Jurassic
- Deltatheridium: Cretaceous
- Jeholodens: mid-Cretaceous
- Megazostrodon: late Triassic and early Jurassic
- Triconodont: Triassic to Cretaceous
- Zalambdalestes: late Cretaceous Although mammals existed alongside the dinosaurs, mammals only began to dominate after the mass extinction of the dinosaurs 65 mya, in the Cenozoic.

In the Paleocene

During the next 8 million years, the Paleocene period (64–58 mya), mammals exploded into the ecological niches left by the extinction of the dinosaurs. Small rodent-like mammals still dominated, but medium and larger-sized mammals evolved.
- Ptilodus: multituberculate
- Pucadelphys andinus: an opposum-like marsupial
- Purgatorius: a primate-like mammal, placental
- Ectoconus: an early hoofed mammal, placental

Classification

Main article: Mammal classification George Gaylord Simpson's classic "Principles of Classification and a Classification of Mammals" (AMNH Bulletin v. 85, 1945) was the original source for the taxonomy listed here. Simpson laid out a systematics of mammal origins and relationships that was universally taught until the end of the 20th century. Since Simpson's 1945 classification, the paleontological record has been recalibrated, and the intervening years have seen much debate and progress concerning the theoretical underpinnings of systematization itself, partly through the new concept of cladistics. Though field work gradually made Simpson's classification outdated, it remained the closest thing to an official classification of mammals.

Standardized textbook classification

A somewhat standardized classification system has been adopted by most current mammalogy classroom textbooks. The following taxonomy of extant and recently extinct mammals is taken from Vaughan et al. (2000). Class Mammalia
- Subclass Prototheria - monotremes: platypus and echidnas
- Subclass Theria - live-bearing mammals
  - Infraclass Metatheria - marsupials
  - Infraclass Eutheria - placentals

McKenna/Bell classification

In 1997, the mammals were comprehensively revised by Malcolm C. McKenna and Susan K. Bell, which has resulted in the "McKenna/Bell classification". McKenna and Bell, Classification of Mammals: Above the species level, (1997) is the most comprehensive work to date on the systematics, relationships, and occurrences of all mammal taxa, living and extinct, down through the rank of genus. The new McKenna/Bell classification was quickly accepted by paleontologists. The authors work together as paleontologists at the American Museum of Natural History, New York. McKenna inherited the project from Simpson and, with Bell, constructed a completely updated hierarchical system, covering living and extinct taxa that reflects the historical genealogy of Mammalia. The McKenna/Bell hierarchical listing of all of the terms used for mammal groups above the species includes extinct mammals as well as modern groups, and introduces some fine distinctions such as legions and sublegions (ranks which fall between classes and orders) that are likely to be glossed over by the layman. The published re-classification forms both a comprehensive and authoritative record of approved names and classifications and a list of invalid names. Click on the highlighted link for a [http://nasa.utep.edu/chih/chklist/mammals/keys/mammtab.htm table comparing the traditional and the new McKenna/Bell classifications of mammals] Extinct groups are represented by †. Class Mammalia
- Subclass Prototheria: monotremes: platypuses and echidnas
- Subclass Theriiformes: live-bearing mammals and their prehistoric relatives
  - Infraclass †Allotheria: multituberculates
  - Infraclass †Triconodonta: triconodonts
  - Infraclass Holotheria: modern live-bearing mammals and their prehistoric relatives
    - Supercohort Theria: live-bearing mammals
      - Cohort Marsupialia: marsupials
      -
- Magnorder Australidelphia: Australian marsupials and the monito-del-monte
      -
- Magnorder Ameridelphia: New World marsupials
      - Cohort Placentalia: placentals
      -
- Magnorder Xenarthra: xenarthrans
      -
- Magnorder Epitheria: epitheres
      -
  - Grandorder Anagalida: lagomorphs, rodents, and elephant shrews
      -
  - Grandorder Ferae: carnivorans, pangolins, creodonts, and relatives
      -
  - Grandorder Lipotyphla: insectivorans
      -
  - Grandorder Archonta: bats, primates, colugos, and tree shrews
      -
  - Grandorder Ungulata: ungulates
      -
    - Order Tubulidentata incertae sedis: aardvark
      -
    - Mirorder Eparctocyona: condylarths, whales, and artiodactyls
      -
    - Mirorder †Meridiungulata: South American ungulates
      -
    - Mirorder Altungulata: perissodactyls, elephants, manatees, and hyraxes

Molecular classification of mammals

Molecular studies based on DNA analysis have suggested new relationships among mammal families over the last few years. The most recent classification systems based on molecular studies have proposed four groups or lineages of placental mammals. Molecular clocks suggest that these clades diverged from early common ancestors in the Cretaceous, but fossils have not been found to corroborate this hypothesis. These molecular findings are consistent with mammal zoogeography: The first divergence was that of the Afrotheria 110–100 mya. The Afrotheria proceeded to evolve and diversify in the isolation of the African-Arabian continent. The Xenarthra, isolated in South America, diverged from the Boreoeutheria approximately 100–95 mya. The Boreoeutheria split into the Laurasiatheria and Euarchontoglires between 95 and 85 mya; both of these groups evolved on the northern continent of Laurasia. After tens of millions of years of relative isolation, Africa-Arabia collided with Eurasia, exchanging Afrotheria and Boreoeutheria. The formation of the Isthmus of Panama linked South America and North America, which facilitated the exchange of mammal species in the Great American Interchange. The traditional view that no placental mammals reached Australasia until about 5 million years ago when bats and murine rodents arrived has been challenged by recent evidence and may need to be reassessed. It should however be noted that these molecular results are still controversial because they are not reflected by morphological data and thus not accepted by many systematists.
- Group I: Afrotheria
  - Order Macroscelidea: elephant shrews (Africa).
  - Order Afrosoricida
  - Order Tubulidentata: aardvark (Africa south of the Sahara).
  - Clade Paenungulata
    - Order Hyracoidea: hyraxes, dassies (Africa, Arabia).
    - Order Proboscidea: elephants (Africa, Southeast Asia).
    - Order Sirenia
- Group II: Xenarthra
  - Order Xenarthra: sloths and anteaters (Neotropical) and armadillos (Neotropical and Nearctic)
- Clade Boreoeutheria
  - Group III Euarchontoglires
    - Superorder Euarchonta
      - Order Scandentia: tree shrews (Southeast Asia).
      - Order Dermoptera: flying lemurs or colugos (Southeast Asia).
      - Order Primates: lemurs, bushbabies, monkeys, apes (cosmopolitan).
    - Superorder Glires
      - Order Lagomorpha: pikas, rabbits, hares (Eurasia, Africa, Americas).
      - Order Rodentia: rodents (cosmopolitan)
  - Group IV: Laurasiatheria
    - Order Insectivora: eulipotyphlan insectivorans
    - Order Chiroptera: bats (cosmopolitan)
    - Order Cetartiodactyla: cosmopolitan; includes former orders Cetacea (whales, dolphins and porpoises) and Artiodactyla (even-toed ungulates, including pigs, hippopotamus, camels, giraffe, deer, antelope, cattle, sheep, goats).
    - Clade Zooamata
      - Order Perissodactyla: odd-toed ungulates
      - Clade Ferae
      -
- Order Pholidota: pangolins, scaly anteaters (Africa, South Asia).
      -
- Order Carnivora: carnivorans (cosmopolitan)

Classification system used in related articles

In light of all the options available, the following classification system has been adopted for use in related articles. Class Mammalia
- Subclass/Order Monotremata: egg-laying mammals
  - Order Monotremata: echidnas and platypus
- Subclass Marsupialia: marsupials
  - Order Didelphimorphia: New World opossums
  - Order Paucituberculata: shrew opossums
  - Order Microbiotheria: Monito del Monte
  - Order Dasyuromorphia: marsupial carnivores
  - Order Notoryctemorphia: marsupial mole
  - Superorder Syndactyla: syndactylous marsupials
    - Order Peramelemorphia: bandicoots and bilbies
    - Order Diprotodontia: koalas, wombats, kangaroos, possums, etc.
- Subclass Placentalia
  - Order Xenarthra: sloths, anteaters, armadillos
  - Order Pholidota: pangolins
  - Superorder Glires
    - Order Rodentia: rodents
    - Order Lagomorpha: rabbits, hares, and pikas
  - Order Macroscelidea: elephant shrews
  - Superorder Archonta:
    - Order Primates: primates
    - Order Scandentia: tree shrews
    - Order Chiroptera: bats
    - Order Dermoptera: colugos
  - Order Insectivora: shrews, tenrecs, moles, hedgehogs, etc.
  - Order Carnivora: dogs, cats, weasels, seals, etc.
  - Superorder Ungulata: ungulates
    - Order Tubulidentata: aardvark
    - Order Hyracoidea: hyraxes
    - Order Proboscidea: elephants
    - Order Sirenia: manatees, dugong
    - Order Perissodactyla: horses, tapirs, rhinoceroses
    - Order Artiodactyla: even-toed ungulates
    - Order Cetacea: whales

References


- McKenna, Malcolm C., and Bell, Susan K. 1997. Classification of Mammals Above the Species Level. Columbia University Press, New York, 631 pp. ISBN 0-231-11013-8
- Nowak, Ronald M. 1999. Walker's Mammals of the World, 6th edition. Johns Hopkins University Press, 1936 pp. ISBN 0-801-85789-9
- Simpson, George Gaylord. 1945. "The principles of classification and a classification of mammals". Bulletin of the American Museum of Natural History, 85:1–350.
- Springer, Mark S., Michael J. Stanhope, Ole Madsen, and Wilfried W. de Jong. 2004. "Molecules consolidate the placental mammal tree". Trends in Ecology and Evolution, 19:430–438. ([http://www.zi.ku.dk/evolbiology/courses/ME04/7_9/springer200-phyl.pdf pdf version])
- Vaughan, Terry A., James M. Ryan, and Nicholas J. Capzaplewski. 2000. Mammalogy: Fourth Edition. Saunders College Publishing, 565 pp. ISBN 0-030-25034-X (Brooks Cole, 1999)
- Wilson, Don E., and Deeann M. Reeder (eds). 1993. Mammal Species of the World. Smithsonian Institution Press, 1206 pp. ISBN 1-560-98217-9

See also


- List of mammals
- List of regional mammals lists
- List of prehistoric mammals
- Mammal classification

External links


- [http://www.nceas.ucsb.edu/~alroy/nafmsd.html North American Fossil Mammal Systematics Database.]
- [http://paleocene-mammals.de/ Paleocene Mammals], a site covering the rise of the mammals
- [http://www.enchantedlearning.com/subjects/mammals/Evolution.shtml Evolution of Mammals], a brief introduction to early mammals
- [http://home.arcor.de/ktdykes/mesomamm.htm The Evolution of Mesozoic Mammals, a Rough Sketch], an informal introduction
- [http://www.carnegiemnh.org/research/news.html Carnegie Museum of Natural History], some discoveries of early mammal fossils
- [http://www.geocities.com/mammal_taxonomy/index.html Mammal Taxonomy], database of mammals of the world, updated each month
- [http://nmnhgoph.si.edu/msw/ Mammal Species of the World], searchable online version of 2nd edition (1993) of Mammal Species of the World zh-min-nan:Chhī-leng tōng-bu̍t ko:포유류 ms:Mamalia ja:哺乳類 simple:Mammal th:สัตว์เลี้ยงลูกด้วยนม

Faunal stage

Faunal stages are a subdivision of geologic time used primarily by paleontologists who study fossils rather than by geologists who study rock formations. Typically, a faunal stage will consist of a series of rocks that contain similar fossils. There will be one or more index fossils that are usually common, easily recognized, and limited to a single, or at most a few, stages. Thus, for example, a North American paleontologist finding fragments of the trilobite Olenellus would identify the beds as being from the Waucoban Stage whereas fragments of a later trilobite such as Elrathia would identify the stage as Albertan. Faunal stages were very important in the 19th and early 20th Century as they were the major tool available for dating rock beds until the development of seismology and radioactive dating in the second half of the 20th Century. Faunal stages are regional. They often include many formations of differing rock types that were being laid down in different environments at the same time. In recent years, regional and global correlations of rock sequences have become relatively certain and there is less need for faunal labels to refine the age of formations. There has been a tendency to use European and, to a lesser extent, Asian, stage names for the same time period world wide even though the faunas in other regions may have little in common with the stage as originally defined. Category:Geologic time scale

Antarctica

:For the Kim Stanley Robinson novel, see Antarctica (novel) Antarctica (from Greek ἀνταρκτικός, "opposite the Arctic") is a continent surrounding the Earth's South Pole. It is the coldest place on Earth and is almost entirely covered by ice; however, it is also the world's largest desert. Although myths and speculation about a Terra Australis ("Southern Land") go back to antiquity, the first commonly accepted sighting of the continent occurred in 1820 and the first verified landing in 1821 by the Russian expedition of Mikhail Lazarev and Fabian Gottlieb von Bellingshausen. (See also History of Antarctica.) With an area of 13,200,000 km², Antarctica is the fifth largest continent, after Asia, Africa, North America, and South America. However, it is by far the smallest in population: indeed, it has no permanent population at all. It is also the continent with the highest average altitude, and the lowest average humidity of any continent on Earth, as well as the lowest average temperature. It has been assigned the Internet ccTLD .aq.

Antarctic climate

.aq Antarctica is the coldest place on earth. Temperatures reach a minimum of between -85 and -90 degrees Celsius in the winter and about 30 degrees higher in the summer months. Weather fronts rarely penetrate far into the continent, leaving the center cold and dry. There is little precipitation over the central portion of the continent, but ice there can last for extended time periods. However, heavy snowfalls are not uncommon on the costal portion of the continent, where snowfalls of up to 48 inches in 48 hours have been recorded. Nearly all of Antarctica is covered by an ice sheet that is, on average, 2.5 kilometers thick. At the edge of the continent, strong katabatic winds off the polar plateau often blow at storm force. In the interior, however, windspeeds are often moderate. Depending on the latitude, long periods of constant darkness, or constant sunlight, mean that climates familiar to humans are not generally available on the continent.

Geography

katabatic wind The continent of Antarctica is located mostly south of the Antarctic Circle, surrounded by the Southern Ocean. Physically Antarctica is divided in two by mountains close to the neck between the Ross Sea and the Weddell Sea. The portion of the continent west of the Weddell Sea and east of the Ross Sea is called Western Antarctica and the remainder Eastern Antarctica, since they correspond roughly to the eastern and western hemispheres relative to the Greenwich meridian. Western Antarctica is covered by the West Antarctic Ice Sheet. See also: Extreme points of Antarctica, Antarctic territories.

Population

It is usually estimated that at a given time there are at least 1,000 people living in Antarctica. This varies considerably with season. Generally, stations use their home country's time zone, but not always; where known, a base's UTC offset is listed. Although Antarctica has no permanent residents, a number of governments maintain permanent research stations throughout the continent. Many of the stations are staffed around the year. These include: staffed
- Akademik Vernadsky Station, Galindez Island, (), ( UKR)
- Amundsen-Scott South Pole Station, South Pole United States Antarctic Program
- Belgrano II, () Laboratory and meteorological station Argentine southernmost base (since 1979).
- Bellingshausen Station, King George Island ()
- Bernardo O'Higgins Station, Antarctic Peninsula, Chilean Army.
- Casey, Vincennes Bay ( Australian Antarctic Division) (UTC+8)
- Comandante Ferraz Station, King George Island ()
- Concordia Research Station, (75° S 123° E),
- Dakshin Gangotri Station, Indian Antarctic Program
- Davis, Princess Elizabeth Land ( Australian Antarctic Division) (UTC+7)
- Dumont d'Urville Station () (UTC+10)
- Eduardo Frei Montalva Station and Villa Las Estrellas, King George Island, Chilean Air Force.
- Esperanza () Laboratory and meteorological station (since 1952). Radio LRA Arcángel, School #38 Julio A. Roca (since 1978), tourist facilities.
- General Artigas Station ()
- Georg von Neumayer Station, () (Atka-Bay) (Alfred Wegener Institute )
- Great Wall Station (), King George Island ()
- Halley Research Station () British Antarctic Survey
- Henryk Arctowski Polish Antarctic Station (), King George Island
- Jubany, (), since 1953 ()
- King Sejong Station (), King George Island, since 1988 ()
- Machu Picchu Research Station, Admiralty Bay, King George Island, summer base established in 1989.
- Macquarie Island ( Australian Antarctic Division)
- Maitri Station, () near Schirmacher Region ( Indian Antarctic Program)
- Marambio Base, () Seymour-Marambio Island. Laboratory, meteorological station, 1.2 km long, 30 m wide landing track (since 1969) () [http://www.marambio.aq website]
- Mawson Station, Mac Robertson Land ( Australian Antarctic Division) (UTC+6)
- McMurdo Station, Ross Island () (UTC+12, follows New Zealand DST)
- Mirny Station () ()
- Mizuho Station () (National Institute of Polar Research )
- Molodezhnaya Station () ()
- Novolazarevskaya Station, Dronning Maud Land () ()
- Orcadas () Orcadas Islands (since 1904)()
- Palmer Station, Anvers Island () (UTC-4, follows Chilean DST)
- Professor Julio Escudero base, King George Island.
- Progress Station () ()
- Rothera Research Station () British Antarctic Survey (UTC-3)
- San Martín Station () (since 1951) Laboratory and Meteorological measurements ()
- SANAE (South African National Antarctic Expeditions), on the Fimbul Coastal Ice Shelf in Queen Maud Land
- Saint Climent Ohridski () (since 1988) Biology Research, Laboratory and Meteorological measurements. First Orthodox Church - St. Ivan Rilski ()
- Scott Base, () Ross Island () (UTC+12, follows New Zealand DST)
- Showa Station () (National Institute of Polar Research ) (GMT+3)
- Troll Station (Norwegian Polar Institute), () Queen Maud Land ()
- Vostok, Antarctica () () (UTC+6)
- Zhongshan (Sun Yet-Sen) Station () () Emilio Marcos Palma was the first person born in Antarctica (Base Esperanza) in 1978, his parents being sent there along with seven other families. Emilio Marcos Palma

Communications

The international dialing code for Antarctica is +672. Antarctica has wireless telephone services. There is a single cell tower using AMPS technology at Argentina's Marambio Base and an Entel Chile GSM tower on King George Island. Communications are otherwise limited to satellite connections. Radio frequencies that can be used are FM2 and shortwave 1.

Military

The Antarctic Treaty prohibits any measures of a military nature in Antarctica, such as the establishment of military bases and fortifications, the carrying out of military maneuvers, or the testing of any type of weapon. It permits the use of military personnel or equipment for scientific research or for any other peaceful purposes. The United States military issues the Antarctica Service Medal to those members of the military or civilians who perform research duty on the Antarctica continent. The medal, including the winter-over bar issued to those who remain on the continent for two complete, six-month seasons, is properly awarded by the United States Congress. The only documented large-scale land military maneuver was "Operación 90," undertaken 10 years before the Antarctic Treaty by the Argentinian military.

See also


- South Pole
- Southern Ocean
- Antarctic Treaty System
- Climate of Antarctica
- Communications in Antarctica
- Demographics of Antarctica
- Ecology of Antarctica
- Economy of Antarctica
- Flags of Antarctica
- History of Antarctica
- Antarctica territories
- List of antarctic and sub-antarctic islands
- Transportation in Antarctica
- Mount Erebus disaster
- Antarctic Stamps
- Diamond dust, an Antarctic optical phenomenon
- Life in the Freezer, a BBC television series on life on and around Antarctica
- Extreme points of Antarctica
- Wildlife of Antarctica - Krill, Penguins, Pinniped (Seals, Sea Lions, Fur seal), Whales
- Ice, Iceberg, Ice shelf, Glacier

External links


- [http://www.70south.com 70South]
- [http://www.ats.org.ar Antarctic Treaty Secretariat]
- [http://www.anetstation.com ANetStation]
- [http://www.add.scar.org The Antarctic Digital Database - a source of digital topographic map data for Antarctica]
- [http://www.ejercito.mil.ar/antartico/historia/antarti_hist.htm Argentine Antarctic history]
- [http://www.aad.gov.au/ Australian Antarctic Division]
- [http://www.antarctica.ac.uk British Antarctic Survey]
- [http://www.comnap.aq/ Council of Managers of National Antarctic Programs (COMNAP)], official homepage.
- [http://www.awi-bremerhaven.de/Polar/index.html German Antarctic Ships and Stations]
- [http://www.loc.gov/rr/international/frd/antarctica/antarctica.html Portals on the World - Antarctica] from the Library of Congress
- [http://www.polarmuseum.sp.ru/Eng/ The Russian State Museum of Arctic and Antarctic]
- [http://www.scar.org The Scientific Committee for Antarctic Research - coordinating body for Antarctic Science]
- [http://members.eunet.at/castaway/stations/aa-bases.html Antarctic Research Stations]
- [http://www.cia.gov/cia/publications/factbook/geos/ay.html The World Factbook – Antarctica] from the U.S. Central Intelligence Agency
- [http://www.70south.com Latest Antarctic news and information by 70South]
- [http://www.planetavivo.org/english/ResearchPrograms/Antarctica/SlideShows/ArdleyIsland/ArdleyIsland1.html Biodiversity at Ardley Island, South Shetland archipelago, Antarctica]
- [http://www.iaato.org International Association of Antarctic Tour Operators (IAATO)] Category:Continents Category:Antarctica Category:Special territories Category:Lists of coordinates ja:南極大陸 ko:남극 ms:Antartika simple:Antarctica th:ทวีปแอนตาร์กติกา zh-min-nan:Lâm-ke̍k-tāi-lio̍k

Glacier

:This article is about the geographical formation. For the professional wrestler, see Ray Lloyd A glacier is a large, long-lasting river of ice that is formed on land and moves in response to gravity. A glacier is formed by multi-year ice accretion in sloping terrain. Glacier ice is the largest reservoir of fresh water on Earth, and second only to the oceans as the largest reservoir of total water. Glaciers can be found on every continent except Australia. Geologic features associated with glaciers include end, lateral, ground and medial moraines that form from glacially transported rocks and debris; U-shaped valleys and corries (cirques) at their heads, and the glacier fringe, which is the area where the glacier has recently melted. cirques

Types of glaciers

cirques There are two main types of glaciers: alpine glaciers, which are found in mountain terrains, and continental glaciers, which are associated with ice ages and can cover large areas of continents. Most of the concepts in this article apply equally to alpine glaciers and continental glaciers. A temperate glacier is one where liquid water is present at least part of the year. Polar glaciers are always below the freezing point. The smallest alpine glaciers form in mountain valleys and are referred to as valley glaciers. Larger ice layers can cover an entire mountain, mountain chain or even a volcano; this type is known as an ice cap. Ice caps feed outlet glaciers, tongues of ice that extend into valleys below, far from the margins of those larger ice masses. Outlet glaciers are formed by the movement of ice from a polar ice cap, or an ice cap from mountainous regions, to the sea. The largest glaciers are continental ice sheets, enormous masses of ice that are not affected by the landscape and extend over the entire surface, except on the margins, where they are thinnest. Antarctica and Greenland are the only places where continental ice sheets currently exist. These regions contain vast quantities of fresh water. The volume of ice is so large that if the Greenland ice sheet melted, it would cause sea levels to rise some six meters all around the world. If the Antarctic ice sheet melted, sea levels would rise up to 65 meters. Plateau glaciers resemble ice sheets, but on a smaller scale. They cover some plateaus and high-altitude areas. This type of glacier appears in many places, especially in Iceland and some of the large islands in the Arctic Ocean, and throughout the northern Pacific Cordillera from southern British Columbia to western Alaska. Tidewater glaciers are glaciers that flow into the sea. As the ice reaches the sea pieces break off, or calve, forming icebergs. Most tidewater glaciers calve above sea level, which often results in a tremendous splash as the iceberg strikes the water. If the water is deep, glaciers can calve underwater, causing the iceberg to suddenly explode up out of the water. The Hubbard Glacier is the longest tidewater glacier in Alaska and has a calving face over ten kilometers long. Yakutat Bay and Glacier Bay are both popular with cruise ship passengers because of the huge glaciers descending to them. Piedmont glaciers occupy broad lowlands at the base of steep mountains, and form when one or more alpine glaciers surge from the confining walls of mountain valleys. The size of piedmont glaciers varies greatly: among the largest is the Malaspina Glacier, which extends along the length of the southern coast of Alaska. It covers more than 5,000 km² of the coastal plain at the foot of the Saint Elias range. And it is only a part of the much bigger Kluane Icecap, which spans the Mount St. Elias and Chugach groups of mountain ranges all the way from the Malaspina Glacier to the Copper River and well into the southwestern Yukon, as well as southeast from the Malaspina towards the Iskut River in British Columbia. The highest alpine glacier in the world is the Siachen Glacier, which is also a zone of political conflict between India and Pakistan.

Formation of glaciers

Siachen Glacier The snow which forms glaciers is subject to repeated freezing and thawing, which changes it into a form of granular ice called névé. Under the pressure of the layers of ice and snow above it, this granular ice fuses into denser firn. Over a period of years, layers of firn undergo further compaction and become glacial ice. Glacial ice contains minute air bubbles as a result, giving it a distinctive blue tint due to Rayleigh scattering. The lower layers of glacial ice flow and deform plastically under the pressure, allowing the glacier as a whole to move slowly like a viscous fluid. Glaciers do not need a slope to flow, being driven by the continuing accumulation of new snow at their source. The upper layers of glaciers are more brittle, and often form deep cracks known as crevasses as they flex. These crevasses make travel over glaciers dangerous. Glacial meltwaters flow throughout and underneath glaciers, carving channels in the ice similar to caves in rock and also helping to lubricate the glacier's movement. In the summer, the melted ice from the glacier alone may be enough to create a stream, and while the glacier may be a barren waste of dense ice, fertile land is often nearby.

Anatomy of a glacier

cave The upper part of a glacier that receives most of the snowfall is called the accumulation zone. As a rule of thumb, the accumulation zone accounts for 60-70% of the glacier's surface area. The depth of ice in the accumulation zone exerts a downward force sufficient to cause deep erosion of the rock in this area. After the glacier is gone, this often leaves a bowl or amphitheater-shaped depression called a cirque. On the opposite end of the glacier, at its foot or terminal, is the deposition or ablation zone, where more ice is lost through melting than gained from snowfall and sediment is deposited. The place where the glacier thins to nothing is called the ice front. The altitude where the two zones meet is called the equilibrium line. At this altitude, the amount of new snow gained by accumulation is equal to the amount of ice lost through ablation. The downward erosive forces of the accumulation zone and the tendency of the ablation zone to deposit sediment also cancel each other out. Erosive lateral forces are not canceled; therefore, glaciers turn v-shaped river-carved valleys into u-shaped glacial valleys. The "health" of a glacier is defined by the area of the accumulation zone compared to the ablation zone. Healthy glaciers have large accumulation zones. Several non-linear relationships define the relation between accumulation and ablation. The worldwide shrinking of 70% of glaciers [http://www.grida.no/climate/ipcc_tar/wg1/064.htm] is among the evidence for global warming. Approximately 30% of glaciers are advancing. Even in very cold climates, there may be unglaciated areas, which receive too little precipitation to form permanent ice. This was the case in most of Siberia, central and northern Alaska and all of Manchuria during glacial periods of the Quaternary, and occurs today in that part of the Andes between 19°S and 27°S above the hyperarid Atacama Desert where, although the mountains reach 6700 metres above sea level, the cold Humboldt Current competely suppresses precipitation. During ice ages, continental glaciers may be as much as 1500 meters thick. A more extreme instance of glacial growth may have occurred during the Snowball Earth period. In the past several centuries the Earth's glaciers have generally been retreating, often dramatically.

Glacial motion

Earth Ice behaves like an easily breaking solid until its thickness exceeds about 50 meters (160 ft). Below that depth the increased pressure causes ice to become plastic and flow. The glacial ice is made up of layers of molecules stacked on top of each other, with relatively weak bonds between the layers. When the stress exceeds the inter-layer binding strength, the layers start to slide past each other. Another type of movement is basal gliding. In this process, the whole glacier moves over the terrain on which it sits, lubricated by thawed ice. As the pressure increases toward the base of the glacier, the melting point of water decreases, and the ice melts. Friction between ice and rock and geothermal heat from the Earth's interior also contribute to thawing. The top 50 meters of the glacier are more rigid. In this section, known as the fracture zone, there are no layers which slide past each other; instead the ice mostly moves as a single unit. Ice in the fracture zone moves over the top of the lower section. When the glacier moves through irregular terrain, cracks form in the fracture zone. These cracks can be up to 50 meters deep, at which point they meet the plastic flow underneath that seals them.

Speed of glacial movement

The speed of glacial displacement is partly determined by friction. Friction makes the ice at the bottom of the glacier move slower than the upper portion. In alpine glaciers, friction is also generated at the valley's side walls, which slows the edges relative to the center. This has been confirmed by experiments in the 19th century, in which stakes were planted in a line across an alpine glacier, and as time passed, those in the center moved further. Mean speeds vary; some have speeds so slow that trees can establish themselves among the deposited scourings. In other cases they can move as fast as many meters per day, as is the case of Byrd Glacier, an overflowing glacier in Antarctica which moves 750-800 meters per year (some 2 meters (6 ft) per day), according to studies using satellites. Many glaciers have periods of very rapid advancement called