Further Reading

De Wit, Maarten J., Chris Roering, Robert J. Hart, Richard A. Armstrong, C. E. J. de Ronde, Rod W. E. Green, Marian Tredoux, Ellie Peberdy, and Roger A. Hart. Formation of an Archean Continent. Nature 357 (1992) 553-562. Kusky, Timothy M. Collapse of Archean Orogens and the Generation of Late- to Post-Kinematic Granitoids. Geology 21 (1993) 925-928. Kusky, Timothy M., Jianghai Li, and Robert T. Tucker. The Archean Dongwanzi Ophiolite Complex, North China Craton 2.505 Billion Year Old Oceanic...

Structural v Stratigraphic Thickness Of Greenstone Belts

Many studies of the stratigraphy of greenstone belts have assumed that thick successions of metamorphosed sedimentary and volcanic rocks occur without structural repetition, and that they have undergone relatively small amounts of deformation. As fossil control is virtually nonexistent in these rocks, stratigraphic correlations are based on broad similarities of rock types and poorly constrained isotopic dates. In pre-1980 studies it was common to construct single stratigraphic columns that...

Solidification Of magma

Just as rocks partially melt to form different liquid compositions, magmas may solidify to different minerals at different times to form different solids (rocks). This process also results in the continuous change in the composition of the magma if one mineral is removed the resulting composition is different. If this occurs, a new magma composition results. The removal of crystals from the melt system may occur by several processes, including the squeezing of melt away from the crystals or by...

Cenozoic Tectonics Of Asia

Many large Mesozoic and Cenozoic basins cover the eastern North China craton and extend northward into Mongolia. The development of these large basins was concentrated in two time periods, the Jurassic to Cretaceous and the Cretaceous to present. An overall NW-SE-trending extensional stress field during formation of these basins was related to changes in convergence rates of India-Eurasia and Pacific-Eurasia combined with mantle upwelling. Two stages of basin formation may have been related to...

Types Of Volcanism In Different Arcs

The most essential part of an island arc is the volcanic center, consisting of a line of volcanic islands comprising volcanic and pyroclastic debris, forming a linear chain about 60-70 miles (100-110 km) above the subducting slab. In island arcs the volcanic rocks are generally of several different types called volcanic series. These include a tholeiitic series, consisting of tholeiitic basalt, andesite, and less common dacite. The calc-alkaline series has basalts rich in alumina, abundant...

Molecular Clouds

Geology Wedge Uplift

Molecular clouds are among the largest structures of interstellar space. They consist of cold and relatively dense (1012 particles cm3) collections of matter in molecular form. Molecules in these clouds can become excited by collision with other particles or by interacting with radiation. When either happens, the molecules reach a higher energy state when they are excited, and when they relax to a lower energy state, they emit a photon that can then be detected by astronomers. Molecules are...

Dust Clouds

Dark areas of the sky can be voids, or alternatively, areas where the light is obscured by cold and relatively dense clouds of dust particles. They typically appear as dark, irregular areas in otherwise starlight areas of the sky. Dark dust clouds are typically about 100 kelvin (equivalent to -173 C, or -279 F), but can be considerably colder, range in size from bigger than Earth's solar system to many parsecs across, and have densities thousands to millions of times greater than surrounding...

Nebulae

Nebulae are areas of interstellar space that appear fuzzy yet are clearly distinguishable from surrounding areas of space, and many of those visible from Earth are concentrated in the plane of the Milky Way Galaxy. Many nebulae are clouds of interstellar gas and dust. In some cases these clouds block the light of stars that are located behind (from the observer's point of view) the nebula, and in other cases the nebulae appear bright and are lit up from the inside, typically by groups of young...

Proterozoic Gneiss Belts And Basins

The Archean cratons of Australia are welded together by several Proterozoic orogenic belts, the most important of which include the Musgrave orogen and its continuation to the west as the Paterson orogen that together link north and south Australia. The Capricorn orogen is located between the Pilbara and Yil-garn cratons convergent tectonism across this belt joined those cratons and their flanking sedimentary basin sequences in the Paleoproterozoic at around 2.2 billion years ago, with remnants...

Devonian strata

In the late silurian and Devonian a major regression affected most of the craton, exposing the underlying rocks to subaerial erosion, except for a few deep basins and narrow seaways. This major unconformity is overlain by a new transgressive sequence known as the Kaskaskia sequence, which, like the two preceed-ing sequences, is marked by a basal quartz sandstone, overlain in turn by a thick carbonate sequence. Much of the continent was again covered by carbonate and shale deposition, and areas...

Different Types Of Supernovas

Enough supernovas have been observed to characterize some differences between them. Some supernovas have very little hydrogen associated with them (called Type-I supernovas), whereas others are hydrogen-rich (Type-II supernovas) and are associated with the star collapse or implosion described above. These two types of supernovas that have observationally different luminosity vs. time curves also have fundamentally different origins. A Type-I supernova, also known as a carbon-detonation...

Hazards of Mud ows Floods Debris Flows and Avalanches

When pyroclastic flows and nu es ardentes move into large rivers, they quickly cool and mix with water, becoming fast-moving mudflows known as lahars. Lahars may also result from the extremely rapid melting of icecaps on volcanoes. A type of lahar in which ash, blocks of rock, trees, and other material is chaotically mixed together is known as a debris flow. some lahars originate directly from a pyroclastic flow moving out of a volcano and into a river, whereas other lahars are secondary and...

The Groundwater System

Groundwater is best thought of as a system of many different parts, some of which act as conduits and reservoirs, and others that serve as offramps and onramps into the groundwater system. Recharge areas are where water enters the groundwater system, and discharge areas are where water leaves the groundwater system. In humid climates recharge areas encompass nearly the land's entire surface (except for streams and floodplains), whereas in desert climates recharge areas consist mostly of the...

Influence Of Longterm Climate Effects On Sea level

Many changes in the Earth's climate that control relative sea level are caused by variations in the amount of incoming solar energy, which in turn are caused by systematic changes in the way the Earth orbits the Sun. These systematic changes in the amount of incoming solar radiation caused by variations in Earth's orbital parameters are known as Milankov-itch cycles, after the Serbian mathematician Milutin Milankovitch, who first clearly described these cycles. These changes can affect many...

Geochronology And The Age Of The Earth

Why do geologists say that the Earth is 4.6 billion years old For many hundreds of years, most people in European, Western, and other cultures believed the Earth to be about 6,000 years old, based on interpretations of passages in the Torah and old Testament. However, based on the principles of unifor-mitarianism outlined by James Hutton and Charles Lyell, geologists in the late 1700s and 1800s began to understand the immense amount of time required to form the geologic units and structures on...

Southern Chile 1960 magnitude

The largest earthquake ever recorded struck the Concepci n area of southern Chile on May 22, 1960. This was a subduction zone earthquake, and a huge section of the downgoing oceanic slab moved during this and related precursors and aftershocks spanning a few days. The main shock was preceded by a large foreshock at 2 45 p.m. on sunday, may 22, which was fortunate because this foreshock scared most people into the streets and away from buildings soon to collapse. Thirty minutes later at 3 15...

Gold

Gold is found in a diverse array of deposit types, ranging from concentrations in quartz veins in igne-ous-metamorphic rocks controlled by the plate tectonic setting, to metamorphic settings, to wide areas called alluvial deposits where streams eroded primary gold sources and deposited them in places where the stream currents slowed and dropped the gold out of suspension. most of the lode gold deposits are found in quartz veins in intrusions, granites, shear zones, and deformed turbidite...

Hawaiian Hot Spot

The most famous hot spot in the world consists of the chain of the Hawaiian Islands, extending northwest to the Emperor Seamount chain. Hawaii is a group of eight major and about 130 smaller islands in the central Pacific Ocean. The islands are volcanic in origin, having formed over a magmatically active hot spot that has melted magmatic channels through the Pacific plate as it moves over the hot spot, forming a chain of southeastward younging volcanoes over the hot spot. Kilauea volcano on the...

Iron Meteorites

Iron meteorites consist of iron, 5-20 percent nickel, and some minor metals, and they contain almost no silicate minerals. They are thought to represent the differentiated cores of large planetesimals or proto- planets that formed in the early solar system in the asteroid belt, grew large enough to melt partially and differentiate into core and mantle and crust, then were broken apart by large impacts exposing the core material to outer space. Iron meteorites therefore represent valuable...

Achondrites

Meteorites Plate Tectonics

Achondrite meteorites resemble typical igneous rocks found on Earth. They formed by crystallizing from a Computer artwork of main asteroid belt of the solar system (not to scale), between orbits of Mars and Jupiter (Mark Garlick Photo Researchers, Inc.) silicate magma and are remnants of larger bodies in the solar system that were large enough to undergo differentiation and internal melting. These meteorites do not contain chondrules or remnant pieces of the early solar system since they...

Precambrian Shield Of Southern India

Southern India consists largely of Precambrian rocks, partly covered by the Deccan flood basalts and thin sedimentary sequences. The shield is made of seven main cratons of Archean age, including the Western Dharwar, Eastern Dharwar, southern Granulite Terrane, Eastern Ghats, Bhandara, singhbhum, and Aravalli cratons. Each of these cratons is somewhat different from the others, and most are now joined along intervening thrust belts or wide orogenic belts of intense deformation and metamorphism....

Straight Channels

Stream channels are rarely straight, and a stream is said to have a straight channel if the ratio of the stream length to valley length is 1.5. Although this ratio, called the sinuosity, seems to have no particular mechanical significance, this measure is useful to describe the shape of stream channels. Many stream channels are straight because they inherit their path from incision into an underlying bedrock fracture, whereas others are relatively straight for short distances. In either case...

Appalachians

The Appalachian Mountain belt extends for 1,600 miles (2,600 km) along the east coast of North America, stretching from the St. Lawrence Valley in Quebec, Canada, to Alabama. Many classifications consider the Appalachians to continue through Newfoundland in maritime Canada, and before the Atlantic Ocean opened, the Appalachians were continuous with the Caledonides of Europe. The Appalachians are one of the best-studied mountain ranges in the world, and understanding of their evolution was one...

Stratigraphic Principles And The Rock Record As Indicators Of Earth History

Stratigraphy is the study of rock strata or layers and is concerned with aspects of the rock layers such as their succession, age relationships, lithologic composition, geometry, distribution, correlation, fossil content, and environments of deposition. The main aim of stratigraphy is to understand and interpret the rock record in terms of paleoenvironments, mode of origin of the rocks, and the causes of similarities and differences between different stratigraphic units. These units can then be...

Knighthood And Baronetcy

Lyell's wife, Mary, died of typhoid fever in 1873. Lyell's own health had begun to fail in 1869. He died on February 22, 1875, and was buried in Westminster Abbey. Considered a classic in geology today, Lyell's Principles of Geology was just as popular during the 19th century, evidenced by the fact that Lyell had just finished writing the 12th edition at the time of his death. Queen Victoria conferred knighthood on Lyell in 1848 and made him a baronet in 1864. He had served as president of the...

Aquifers

Aquifers are any body of permeable rock or regolith saturated with water through which groundwater moves. The term aquifer is usually reserved for rock or soil bodies that contain economical quantities of water that are extractable by existing methods. The quality of an aquifer depends on two main qualities, porosity and permeability. Porosity is a measure of the total amount of open void space in the material. Permeability refers to the ease at which a fluid can move through the open-pore...

Prevention of Downslope Flows

Slopes can be reduced by removing material, reducing the potential for landslides. If this is not possible, the slope can be terraced, which decreases runoff and stops material from falling all the way to the base of the slope. slopes can also be covered with stone, concrete, or other material that can reduce infiltration of water, and reduce erosion of the slope material. Retaining walls can be built to hold loose material in place, and large masses of rocks can be placed along the base of the...

Hazardous Elements Minerals And Materials

Many of the more than 100 naturally occurring elements are toxic to humans in high doses, and some occur in high concentrations in the soil. The same elements may be beneficial or even necessary in small, dilute doses and pose little or no threat in intermediate concentrations. Most elements show similar toxicity effects on humans, although not all are toxic in high doses. Understanding the effects of trace elements in the environment on human health is the realm of the huge and rapidly growing...

Iceland Hot Spot

The mid-Atlantic ridge rises above sea level on the North Atlantic island of Iceland, lying 178 miles (287 km) off the coast of Greenland and 495 miles (800 km) from the coast of Scotland. Iceland has an average elevation of more than 1,600 feet (500 m), and owes its elevation to a hot spot interacting with the midocean ridge system beneath the island. The mid-Atlantic ridge crosses the island from southwest to northeast and has a spreading rate 1.2 inches per year (3 cm yr), with the mean...

Summary

The chances of experiencing a large meteorite impact on Earth are small, but the risks associated with large impacts are extreme. Small objects hit the Earth many times every day but burn up in the atmosphere. Events that release enough energy to destroy a city happen about once every thousand years, while major impacts that can significantly alter the Earth's climate happen every 300,000 years. Truly catastrophic impacts that cause mass extinctions, death of at least 25 percent of the world's...

Southern Granulite Terrane

The southern tip of the Indian subcontinent comprises the Southern Granulite terrane, a region of complexly and strongly metamorphosed granulite facies gneisses, as well as amphibolite facies gneisses and lower-grade sedimentary sequences. The Southern Granulite terrane is bounded to the north by the Eastern and Western Dharwar cratons. Rock types in the Southern Granulite terrane are highly unusual and include a suite of metamorphic rocks derived from older sedimentary, volcanic, and gneissic...

Stratigraphic Classification

Because rocks laid down in succession each record environmental conditions on the Earth when they were deposited, experienced geologists can read the record in the stratigraphic pile like a book recording the history of time. Places like the Grand Canyon are especially spectacular because they record billions of years of history. Classical stratigraphy is based on the correlation of distinct rock stratigraphic units, or unconformity surfaces, that are internally homogeneous and occur over large...

Loess

Loess, silt and clay deposited by wind, forms a uniform blanket that covers hills and valleys at many altitudes, distinguishing it from deposits of streams. strong winds that blow across desert regions sometimes pick up dust made of silt and clay particles and transport them thousands of miles (thousands of km) from their source. For instance, dust from China is found in Hawaii, and the sahara Desert commonly drops dust in Europe. This dust is a nuisance, has a significant influence on global...

Biogeography And Paleogeography

Biogeography is the study of the geographic distribution of plants and animals, and paleogeography is the study of the past distribution of plants, animals, landmasses, mountains, basins, and climate belts. The distribution of organisms may be explained by one of two general theories. The dispersal theory in biogeography states that a specific group of organisms was created at an initial center spot and radiated outward, during which time specific lineages evolved as they migrated. An...

Hubble image of M51 Whirlpool Galaxy dated November 7 2002 NASA Goddard Space Flight Center

Most of the stars in elliptical galaxies appear to be old, relatively cold, reddish low-mass stars, similar to the stars in the halo of the Milky Way and other spiral galaxies. Ellipticals are therefore old systems in which the gas and dust was all swept up by the star systems long ago, and the stars are moving about in irregular paths within the elliptical mass. As with most generalized statements, there are exceptions. Recent observations have shown that some giant elliptical...

Baffling Marine Geology DiscovERIES

In July 1950 a group of scientists studying the sea-floor of the Pacific ocean made surprising discoveries that influenced the formulation of Hess's developing ideas about the origin and evolution of ocean basins. scientists believed that the oceanic crust was mostly flat and extremely thick owing to the accumulation of billions of years of sediment from continental erosion. Using explosives and seismic waves, the crew determined the thickness of the oceanic crust to be about four miles (7 km)....

The History Of Life And Mass ExTinctions

Life on Earth has evolved from simple prokaryotic organisms such as Archaea that appeared on Earth by 3.85 billion years ago. Life may have been here earlier, but the record is not preserved, and the method by which life first appeared is also unknown and the subject of much thought and research by scientists, philosophers, and religious scholars. The ancient Archaea derived energy from breaking down chemical bonds of carbon dioxide, water, and nitrogen, and anaerobic archaeans have survived to...

Tsunami nightmare

One of the worst natural disasters of the 21st century unfolded on December 26, 2004, following a magnitude 9.0 earthquake off the coast of northern Sumatra in the Indian Ocean. The earthquake was the largest since the 1964 magnitude 9.2 event in southern Alaska and released more energy than all the earthquakes on the planet in the last 25 years combined. During this catastrophic earthquake, a segment of the seafloor the size of the state of California, lying above the Sumatra subduction zone...

On river dynamics

The long history of flooding and attempted flood-control measures along the Mississippi River basin had taught engineers valuable lessons on how to manage flood control on river basins. Levees are commonly built along riverbanks to protect towns and farmlands from river floods. These levees usually succeed at the job they were intended to do, but they also cause other collateral effects. First, the levees do not allow waters to spill onto the floodplains, so the floodplains do not receive the...

Work In The Petroleum Industry

By the end of World War I Holmes had written three books but was still only a demonstrator at Imperial College. In 1918 the Holmeses had their first child, Norman, and a demonstrator's income was not sufficient to support the family. The Yomah Oil Company hired Holmes as chief geologist with the promise of a much larger salary. His family moved to Burma in November 1920 and settled in Yenangyaung, where Holmes spent two years frantically searching for new oil finds to save the struggling...

Russian East European Craton

The Russian or East European craton is well exposed in the Baltic states and in the Ukrainian shield, but it is mostly buried beneath late Precambrian to Pha-nerozoic cover in the Russian craton. The amalgamated East European craton, which formed the core of the Baltica block in the Proterozoic supercontinents of Rodinia and Gondwana, consisted of the Fen-noscandian block (Baltic shield) in the northwest, the Volgo-Uralia block in the east, and the Sarmatia block in the south. The Baltic shield...

Geothermal Energy In Regions With Geysers

Geysers, hot springs, and fumaroles are associated with regions of elevated temperature at depth, and in some cases these high temperatures have been exploited for geothermal energy. Temperatures in the Earth generally increase downward at 90 -250 F (30 -140 C) per mile (68-212 F 20 -100 C per km), following the geothermal gradient for the region. some regions near active volcanic vents and deep-seated plutons have even higher geothermal gradients and are typified by abundant fumaroles and hot...

Types Of Surface Subsidence And Collapse

Some subsidence occurs because of processes that happen at depths of thousands of feet beneath the surface, and is referred to as deep subsidence. Other subsidence is caused by shallow near-surface pro cesses and is known as shallow subsidence. Tectonic subsidence is a result of the movement of the plates on a lithospheric scale, whereas human-induced subsidence refers to cases where the activities of people, such as extraction of fluids from depth, have resulted in lowering of the land...

Climate and Seasonality

Variations in the average weather at different times of the year are known as seasons, controlled by the average amount of solar radiation received at the surface in a specific place for a certain time. several factors determine the amount of radiation received at a particular point on the surface, including the angle at which the sun's rays hit the surface, the length of time the rays warm the surface, and the distance to the sun. As the Earth orbits the sun approximately once every 365 days,...

Oort Cloud

The oort Cloud is a roughly spherical region containing many comets and other objects, extending from about 60 A.u. to beyond 50,000 A.u., or about 1,000 times the distance from the sun to Pluto, or about one light year. This distance of the outer edge of the solar system is also about one quarter of the way to the closest star neighbor, Proxima Centauri. The oort Cloud is thought to be the source for long- period comets and Halley-type comets that enter the inner solar system. It contains...

Cenozoic Tectonics And Climate

Cenozoic global tectonic patterns are dominated by the opening of the Atlantic Ocean, closure of the Tethys Ocean, and formation of the Alpine-Himalayan Mountain System, and mountain building along the western North American cordillera. Uplift of mountains and plateaus and the movement of continents severely changed oceanic and atmospheric circulation patterns, changing global climate patterns. As the North and South Atlantic Oceans opened in the Cretaceous, western North America was...

Valdez Alaska 1964 magnitude

One of the largest earthquakes ever recorded struck southern Alaska at 5 36 p.m. on March 27, 1964, second in the amount of energy released only to the 1960 Chile earthquake. The energy released during the Valdez earthquake was more than the world's largest nuclear explosion and greater than the Earth's total average annual release of seismic energy, yet, remarkably, only 131 people died during this event. Damage is estimated at 240 million (1964 dollars), a remarkably small figure for an...

Admired And Honored

Beginning in 1962 Hess chaired the Space Science Advisory Board of the National Academy of Sciences. The board's responsibility was to advise NASA. In 1966 he was at Woods Hole, Massachusetts, chairing a meeting to discuss the scientific objectives of lunar exploration when he began having chest pains. He died of a heart attack on August 25, 1969, and was buried at the Arlington National Cemetery. Hess was elected to membership of several academic societies including the National Academy of...

San Francisco 1906 magnitude

Perhaps the most infamous earthquake of all time is the magnitude 7.8 temblor that shook San Francisco at 5 12 a.m. on April 18, 1906, virtually destroying the city, crushing 315 people to death and killing 700 people throughout the region. Many of the unrein-forced masonry buildings that were common in San Francisco immediately collapsed, but most steel and wooden frame structures remained upright. Ground shaking and destruction were most intense where structures were built on areas filled in...

Principles And Elements

Geologists of the time were prepared to reject Werner's ideas for Hutton's, but they needed a push. They were ready to accept that basalt was of igneous origin but more hesitant to accept uniformity of geological processes of the past and the present and of uniform gradual rates of change. Lyell published Principles of Geology An Attempt to Explain the Former Changes in the Earth's Surface by Reference to Causes Now in Operation, which appeared in three volumes between 1830 and 1833 and is now...

Final Years

Having accomplished his two career goals of dating the Earth and constructing a geological timescale that could be applied to common rocks, Holmes concentrated on his professorial duties. In 1943 the university of Edinburgh appointed him regius professor of geology, a position subsidized by the king of England. The outbreak of World War II forced Holmes to reduce his geology course from one year to six months. Though it would have saved lecture time to assign students reading material before...

Timelines And Diachronous Boundaries

In many sedimentary systems, such as the continental shelf, slope, and rise, different types of sediments are deposited in different places at the same time. We can draw time lines through these sequences to represent all the sediments deposited at a given time or to represent the old sediment water interference at a given time. In these types of systems, the transition from one rock type to another, such as from the sandy delta front to the marsh facies, will be diachronous in time (it will...

Coastal Lagoons

Lagoons are a special, rather rare class of restricted coastal bays that are separated from the ocean by an efficient barrier that blocks any tidal influx, and they do not have significant freshwater influx from the mainland. Water enters lagoons mainly from rainfall and occasional storm wash-over. Evaporation from the lagoon causes their waters to have elevated salinity and distinctive environments and biota. most lagoons are elongate parallel to the coast and separated from the ocean by a...

Hazards of Volcanicinduced Earthquakes and Tsunamis

Minor earthquakes generally accompany volcanic eruptions. The earthquakes are generated by magma forcing its way upward through cracks and fissures into the volcano from the magma chamber at depth. Gas explosions in the magma conduits under the volcano generate other earthquakes. The collapse of large blocks of rock into calderas or the shifting of mass in the volcano may also initiate earthquakes. some of these earthquakes happen with a regular frequency, or time between individual shocks, and...

Pakistan October 8 2005 magnitude

At 8 50 a.m. on saturday, october 8, 2005, remote areas of northern Pakistan, north of Islamabad and neighboring Afghanistan, were hit by a major earthquake that caused catastrophic damage to a wide area, largely because of the inferior construction of buildings throughout the region. This earthquake killed more than 86,000 people and injured more than 69,000, leaving about 4 million homeless as the freezing cold of the Kashmir winter set in to the mountainous region. Worst hit was the...

Intertidal Flats

Many coastlines have flat areas within the tidal range sheltered from waves, dominated by mud, and devoid of vegetation that are accumulating sediment, known as intertidal (or just tidal) flats. The width of tidal flats depends on the tidal range and the shape and morphology of the coastline or bay where they are located. some large bays with large tidal ranges, such as the Bay of Fundy in eastern Canada, are dominated by tidal flats. Tidal flats are typically flat areas cut by many channels...

Baltic Shield

The Baltic (Fennoscandian) shield is an Archean cra-ton divided into three distinct parts. The northern, Lapland-Kola province consists mainly of several previously dispersed Archean crustal terranes that together with the different Paleoproterozoic belts have been involved in a collisional-type orogeny at 2.0 to 1.9 billion years ago. A central, northwest-trending segment known as the Belomorian mobile belt is occupied by assemblages of gneisses and amphibo-lites. This part of the Baltic...

Andes

Rio Plata Craton

The Andean mountain chain is a 5,000-mile- (8,000km-) long belt of deformed igneous, metamorphic, and sedimentary rocks in western south America, running generally parallel to the coast, between the Caribbean coast of Venezuela in the north and Tierra del Fuego in the south. some sections are characterized by active volcanoes, others by their absence. Most of the Andes are located above the subducting Nazca plate except for the southern Andes, which are located above the subducting Antarctic...

Chilimanzi Suite

The Chilimanzi suite of K-rich granitoids is one of the last magmatic events in the Zimbabwe craton, with reported ages of 2.57 to 2.6 billion years. These granites appear to be associated with a system of large intracontinental shear zones that probably controlled their position and style of intrusion. These relatively late structures are related to north-northwest to south-southeast shortening and associated southwestward extrusion of crust during the continental accretion and collision as...

Core Contraction And Hydrogen Shell Burning

As the helium in the core builds up it cannot burn, since it requires much higher temperatures to fuse than does hydrogen. The result is that when the hydrogen is used up, the core contracts, since the gas pressure without high temperatures from nuclear fusion is not sufficient to counteract the force of gravity. The shrinkage of the core then releases gravitational potential energy that creates heat, raising the temperature of the core. As the core grows increasingly hot in this way (but not...

Interstellar Cloud

Stars that are close to a solar mass start their evolution as an ordinary, dense, and cold interstellar cloud that may be tens of parsecs across (1 parsec equals 3.3 light years), having temperatures of about 10 K, and densities of around 109 particles per cubic meter. The amount of mass in these types of interstellar clouds may be thousands or millions of times a solar mass at this stage. Typical giant molecular clouds that collapse to form solar-type stars are 6,000,000 solar masses and 100...

Transform Boundaries In The Oceans

Transform plate boundaries in the oceans include the system of ridge-ridge transform faults that are an integral part of the mid-ocean ridge system. Magma upwells along the ridge segments, cools and crystallizes, becoming part of one of the diverging plates. The two plates then slide past each other along the transform fault between the two ridge segments, until the plate on one side of the transform meets the ridge on the other side of the transform. At this point, the transform fault is...

Drying Of The American Southwest

A drought is a prolonged lack of rainfall in a region that typically experiences a significant amount of precipitation. If a desert normally receives a small amount of rainfall, and it still is getting little rainfall, then it is not experiencing a drought. In contrast, a different area that normally receives more rainfall than the desert may be experiencing a drought if it normally receives significantly more rainfall than it is at present, even if it still experiences more rainfall than the...

Jet Streams

Jet streams are high-level, narrow, fast-moving currents of air typically thousands of kilometers long, hundreds of kilometers wide, and a couple of miles (several kilometers) deep. Jet streams typically form near the tropopause, six to nine miles (10-15 km) above the surface, and can reach speeds of 115-230 miles per hour (100-200 knots). Rapidly moving cirrus clouds often reveal the westerly jet streams moving air from west to east. several jet streams are common the subtropical jet stream...

Landslideinduced Tsunamis of the Canary Islands Atlantic Ocean

The Canary Islands form a hot-spot chain of small rugged volcanic islands off the northwest coast of Africa. They constitute two provinces of Spain, Santa Cruz de Tenerife and Las Palmas. The high est point on the islands is Mt. Teide on Tenerife at 12,162 feet (3,709 m) above sea level, although the volcanoes actually rise more than 10,000-13,000 feet (3,000-4,000 m) from the seafloor before the rise above sea level. The Canary Islands are hotspot type shield volcanoes, very similar to Hawaii,...

Polar

Polar lows are hurricane- or gale-strength storms that form over water behind (poleward) the main polar front. They can form over either the Northern or Southern Hemisphere oceans but are a larger menace to the more populated regions around the North Atlantic, North Sea, and Pacific Ocean, as well as the Arctic Ocean. Most polar lows are much smaller than tropical and midlatitude cyclones, with diameters typically fewer than 600 miles (1,000 km). Like hurricanes, many polar lows have spiral...

Types Of Island And Convergent Margin Arcs

There are major differences in processes that occur at continental or Andean-style versus oceanic or island arc systems, also known as Marianas-type arcs. Andean-type arcs have shallow trenches, fewer than four miles (6 km) deep, whereas marianas-type arcs typically have deep trenches reaching seven miles (11 km) in depth. most Andean-type arcs subduct young oceanic crust and have very shallow-dipping subduction zones, whereas Marianas-type arcs subduct old oceanic crust and have steeply...

Kinds Of Metamorphism

Metamorphism is a combination of chemical reactions induced by changing pressure and temperature conditions and mechanical deformation caused by differential stresses. The relative importance of physical and chemical processes changes with meta-morphism in different tectonic settings. Near large plutons or hot igneous intrusions, rocks are heated to high temperatures without extensive mechanical deformation. These elevated temperatures cause rocks next to plutons to grow new minerals, but these...

Kalaharicraton

Southern Africa's Kalahari craton is composed of two older cratons, the Kaapvaal and Zimbabwe, that collided and were sutured 2.5 billion years ago along the Limpopo belt and have acted as a single craton since that time. For times before 2.5 billion years ago, therefore, the two parts (Kaapvaal and Zimbabwe cratons) are discussed separately, but from True-color composite satellite image of Africa from data collected by the Thematic Mapper instrument on an American Landsat satellite. The Sahara...

Physical Properties Of The

The Sun contains no solid material, but the apparent surface visible as a glowing solar disk is known as the photosphere. Above the photosphere is the Sun's lower atmosphere, called the chromosphere, and extending far past that is the corona, an outer atmosphere (visible during eclipses) that gradually merges into the solar wind and consists of particles that flow through the whole solar system. Extending below the photosphere toward the deep interior of the Sun are three more main zones. The...

Causes Of Shortterm Climate Change

The IPCC issued new reports, Climate Change 2007, in 2007 revealing that concentrations of some greenhouse gases have increased dramatically as a result of human activities, mostly starting with the early industrial revolution around 1750 and accelerating in the late industrial revolution around 1850. The greenhouse gases that show the most significant increases are carbon dioxide, methane, and nitrous oxide. Carbon dioxide (C02), the most significant anthropogenic greenhouse gas, is produced...

Kinetic Impact Strategies

One of the alternative strategies that may be effective in deflecting an asteroid from Earth's orbit is to send a massive spacecraft to collide with the asteroid, altering its momentum and removing it from the collision course. This strategy is currently the object of a major study and mission, called Don Quijote, by the European Space Agency. Early results from this mission have shown that it is possible, and a model of the deflection of near-Earth asteroid 99942 Apophis shows that it would...

Desert Landforms

Desert landforms are some of the most beautiful on Earth, often presenting bizarre sculpted mountains, steep walled canyons, and regional gravel plains. They can also be some of the most hazardous landscapes on the planet. The regolith, or mixture of soil and altered bedrock in deserts is thin, discontinuous, and much coarser-grained than in moist regions, and is produced predominantly by mechanical weathering. Chemical weathering is only of minor importance because of the rare moisture. Also...

Pacific Plate Subduction

Subduction along the Pacific margin of China was active from 200 to 100 Ma, soon after closure of the ocean basins on the northern side of the North China craton. Westward-directed oblique subduction was responsible for the generation of arc magmas, deformation, and possibly mantle hydration during this interval. Although the duration and history of Mesozoic subduction beneath the eastern margin of China is not well known, the active margin stepped outward by the Cenozoic, from which a better...

Survey Of Impact Craters On Earth And The Moon

Map Largest Known Crater Earth

Impact craters are known from every continent including Antarctica. Several hundred impact craters have been mapped and described in detail by geologists, and some patterns about the morphology, shape, and size of the craters have emerged from these studies. The most obvious variations in crater style and size are related to the size of the impacting meteorite, but other variations depend on the nature of the bedrock or cover, the angle and speed of the impact, and what the impactor was rock or...

Silica and Coal Dust

Other minerals can be hazardous if made into small airborne particles that can lodge in the lungs. As with asbestos, both silica- and coal-mining operations release large amounts of dust particles into the air, also known, respectively, as quartz dust and coal dust. Workers exposed to these dusts are at risk for diseases broadly similar to asbestosis. Quartz dust is commonly produced during rock drilling and sandblasting operations. These practices produce airborne particles of various sizes,...

Cretaceous Volcanics And The Marion Hot Spot

On the southern side of the island of Madagascar, the shallow-water Madagascar plateau extends 500 miles (800 km) south along the Marion hot spot track to Marion Island. The volcanics associated with this hot spot track correlate with the Late Cretaceous (90 Ma) volcanics abundant on the island, associated with the separation of Madagascar from the Seychelles and India. They become younger progressively to the south to zero-age volcanic on Marion Island. Madagascar was most likely flat and near...

Rainshadow Deserts

A third type of desert is found on the leeward, or back, side of some large mountain ranges, such as the sub-Andean Patagonian Gran Chaco and Pampas of Argentina, Paraguay, and Bolivia. A similar effect is partly responsible for the formation of the Mojave and Sonoran Deserts of the United States. These deserts form because as moist air masses move toward the mountain ranges, they must rise to move over the ranges. As the air rises it cools, and cold air cannot hold as much moisture as warm...

Vredefort Impact Structure South Africa

The Vredefort dome of South Africa is one of the world's largest and oldest known, well-preserved impact structures. Located in the late Archean Wit-watersrand basin, the Vredefort dome is a large, multiring structure with a diameter of 87 miles (140 km) formed by the impact of a meteorite 1.97 billion years ago. The geology and structure of the Vredefort dome is complex, and its origin was the subject of debates for many years. The crater is characterized by a series of concentric rims of rock...

Can Desalination Help SolvE The Water Crisis

With the hydrologie cycle changing through climate change and increased water use, it is important to find new sources of water. Desalination includes a group of water-treatment processes that remove salt from water it is becoming increasingly more important as freshwater supplies dwindle and population grows, yet desalination is exorbitantly expensive and cannot be afforded by many countries. A number of different processes can accomplish desalination of salty water, whether it comes from the...

Gravity anomalies potential Field Studies

Gravity anomalies are the difference between the observed value of gravity at a point and the theoretically calculated value of gravity at that point, based on a simple gravity model. The value of gravity at a point reflects the distribution of mass and rock units at depth, as well as topography. The average gravitational attraction on the surface is 32 feet per second squared (9.8 m s2), with one gravity unit (g. u.) being equivalent to one ten-millionth of this value. Another older unit of...

Solar Core

The energy from the Sun comes from nuclear reactions in its core, generating a luminosity of 4 x 1026 W, or 2 x 104 W kg. The Sun has been producing approximately this vast amount of energy for the past 4.5 billion years. For the entire lifetime of the Sun, the total amount of energy generated has been 3 x 1013 joule kg. The generation of this energy has been remarkably steady and is expected to continue for another 5 billion years, through the process of nuclear fusion. Fusion works by...

South China Craton

The South China craton is divided into the Yangtze craton and the Cathaysia block, joined together in a plate collision in the late Mesoproterozoic. Radio-metric dating of two ophiolite suites in the eastern part of the suture between the Yangtze and Cathay-sia blocks gives ages of 1.03 to 1.02 billion years for the age of this collision. Late Mesoproterozoic suture zones have been also reported from the northwestern and northern margins of the Yangtze block. An ophi-olitic m lange in western...

Siberian Traps

A large part of the central Siberian plateau northwest of Lake Baikal is covered by a thick series of mafic volcanic flows. They are more than half a mile thick (1 km) over an area of 210,000 square miles (543,900 km2) but have been significantly eroded from an estimated volume of 1,240,000 cubic miles (5,168,545 km3). This extraordinary sequence of lavas was erupted over a remarkably short period of less than 1 million years, 250 million years ago, at the Permian-Triassic boundary. Within the...

Hurricane Andrew 1992

Hurricane Andrew was the second-most destructive hurricane in U.S. history, causing more than 30 billion in damage in August 1992. Andrew began to form over North Africa and grew in strength as trade winds drove it across the Atlantic. On August 22 Andrew had grown to hurricane strength and moved across the Bahamas with 150-mile-per-hour (241 km hr) winds, killing four people. On August 24 Andrew smashed into southern Florida with a nearly 17-foot (5.2-m) high storm surge, steady winds of 145...

Grenville belts and the rodinia supercontinent

The Proterozoic saw the development of many continental-scale orogenic belts, many of which have been recently recognized to be parts of global-scale systems that reflect the formation, breakup, and reassembly of several supercontinents. Paleoproterozoic orogens include the Wopmay in northern Canada, interpreted to be a continental margin arc that rifted from North America, then collided soon afterward, closing the young back arc basin. There are many 1.9-1.6-Ga orogens in many parts of the...

Lematre Georges 18941966 Belgian

Cosmologist Georges Lema tre is most famous for proposing the theory of the big bang in 1933. He was born July 17, 1894, in Charleroi, Belgium, where he studied civil engineering and obtained a Ph.D. for his dissertation, L'Approximation des fonctions de plusieurs variables r elles (Approximation of functions of several real variables). He was ordained in 1923 as a Catholic priest before moving to Cambridge, United Kingdom, to study astrophysics at St. Edmund's College. He then moved to the...

Juvenile island arc accretion

Many Archean granite-greenstone terranes are interpreted as juvenile island arc sequences that grew above subduction zones and later amalgamated during collisional orogenesis to form new continental crust. The island arc model for the origin of the continental crust is supported by geochemical studies that show the crust has a bulk composition similar to arcs. Island arcs are extremely complex systems that may exhibit episodes of distinctly different tectonics, including accretion of ophiolite...

Coastal Deserts

Some deserts are located along coastlines, where intuition would seem to indicate that moisture should be plentiful. The driest place on Earth is the Atacama Desert, however, located along the coast of Peru and Chile. The Namib Desert of southern Africa is another coastal desert, known legendarily as the skeleton Coast, because it is so dry that many of the large animals that roam out of the more humid interior climate zones perish there, leaving their bones sticking out of the blowing sands....

Dynamics Of Stream Flow

Streams are dynamic systems and constantly change their channel patterns and the amount of water (discharge) and sediment being transported in the system. streams may transport orders of magnitude more water and sediment in times of spring floods, as compared with low-flow times of winter or drought. since streams are dynamic systems, as the amount of water flowing through the channel changes, the channel responds by changing its size and shape to accommodate the extra flow. For instance, in a...

Northern Hemisphere snow cover

Graphs of global average temperature, sea level, and snow cover for the past 160 years (Data from IPCC 2007) Spruce killed by spruce bark beetle near Homer, Alaska (Peter Essick Aurora Getty Images) Spruce killed by spruce bark beetle near Homer, Alaska (Peter Essick Aurora Getty Images) Northern and the Southern Hemispheres. Changes in the ice caps on Greenland and Antarctica show an increased outflow of glacial ice and meltwater, so melting of the polar ice caps is very likely contributing to...

The Hydrologic Cycle

The water cycle describes the sum of processes operative in the hydrosphere, a dynamic mass of liquid continuously on the move between the different reservoirs on land and in the oceans and atmosphere. The hydrosphere includes all the water in oceans, lakes, streams, glaciers, atmosphere, and groundwa-ter, although most water is in the oceans. The hydro-logic, or water, cycle encompasses all of the changes, both long- and short-term, in the Earth's hydrosphere. It is powered by heat from the...

Beauty And The Beach Rethinking Coastal Living

Civilized societies have built villages, cities, and industrial sites near the sea for thousands of years. Coastal settings offer beauty and commercial convenience but also invite disaster with coastal storms, tsunami, and rising sea levels. In 2004 and 2005 the world witnessed two furious incursions of the sea into heavily populated coastal regions, killing hundreds of thousands of people and causing trillions of dollars in damage. Coastal communities are experiencing early stages of a new...

Radon

Radon is a poisonous gas released during radioactive decay of the uranium decay series. Radon is a heavy gas, and it presents a serious indoor hazard in every part of the country because it accumulates in poorly ventilated basements and well-insulated homes that are built on specific types of soil or bedrock rich in uranium minerals. Radon causes lung cancer, and since it is an odorless, colorless gas, its presence can go unnoticed in homes for years. However, the hazard of radon is easily...

Emission Nebulae

The sections above focused on the formation of stars from the collapse of interstellar dust clouds but did not focus on the effects these processes have on the surrounding intergalactic medium. Star formation as described above does not usually result in the formation of just one star, but rather a group or cluster of stars with similar characteristics and ages in a region that represents the original collapsed interstellar cloud. The more massive the original collapsed dust cloud, the more new...

Flash Floods

Flash floods result from short periods of heavy rainfall and are common near warm oceans, along steep mountain fronts in the path of moist winds, and in areas prone to thunderstorms. They are well known from the mountain and canyon lands of the U.S. desert Southwest and many other parts of the world. Some of the heaviest rainfalls in the United States have occurred along the Balcones escarpment in Texas. Atmospheric instability in this area often forms along the boundary between dry desert air...

Namib desert and the skeleton coast

Namibia's Atlantic coastline is known as the skeleton coast, named for the suffering and death that beset many sailors attempting to navigate the difficult waters swept by the cold Benguela current, which moves along the coast, and warm winds coming off the Namib and Kalahari Deserts. The coastline is littered with numerous shipwrecks, testifying to the difficult and often unpredictable nature of shifting winds and ocean currents. Giant sand dunes of the Namib sand sea reach to the coast, and...

Mount St Helens 1980 and the Cascades Today

The most significant eruption in the contiguous united states in the past 90 years is that of Mount st. Helens in 1980, a mountain that had lain dormant for 123 years. The volcano is part of the active Cascade volcanic arc, a continental-margin arc built on the western coast of North America above where the minor Juan de Fuca plate is being subducted beneath North America. The arc is relatively small (about 1,200 miles, or 2,000 km, long), and stretches from Lassen Peak in California to Mount...

Rapid Changes In Ocean Circulation Patterns And Cumate Change

World Map London

Some models of climate change show that patterns of ocean circulation can suddenly change and cause global climate conditions to switch from warm to cold, or cold to warm, over periods of a few decades. Understanding how fast climate can shift from a warm period to a cold, or cold to a warm, is controversial. The record of climate indicators is incomplete and difficult to interpret. Only 18,000 years ago the planet was in the midst of a major glacial interval, and since then global average...

Glaciation And Glacial Landforms

Glaciation is the modification of the land's surface by the action of glacial ice. When glaciers move over the land's surface, they plow up the soils, abrade and file down the bedrock, carry and transport the sedimentary load, steepen valleys, then leave thick deposits of glacial debris during retreat. In glaciated mountains a distinctive suite of landforms results from glacial action. Glacial stria- tions are scratches on the surface of bedrock, formed when a glacier drags boulders across the...