Brief History Of Astronomy

Ancient cultures were fascinated with the heavens, and astronomy developed into one of the earliest sciences as these cultures formalized their studies of the night skies. Much of the work of these early astronomers focused on observations and predictions of the motions of objects visible to the naked eye, and some cultures erected large monuments that likely have astronomical significance. Early Jewish, Chinese, and other cultures established calendars based on observations and calculations of...

Young Geochronologist

Holmes earned a National Scholarship Award in physics and enrolled at the Royal College of Science in London in 1907. The curriculum required all students to take mathematics, mechanics, chemistry, and physics during their first year, and Holmes took an elective geology course in his second year. The president of the Geological Society, William Watts, taught the course and enticed Holmes to change his course of study during his third year. Fortuitously, Robert J. Strutt (1875-1947) from the...

Chondrites

Chondrites are meteorites that have chemical compositions similar to that of the Sun. Since the Sun makes up about 99 percent of the mass of the solar system, it is assumed that the composition of the Sun represents the average composition for the entire solar system, and that this average composition resembles the original composition of the solar system when it was formed. Therefore since chondrites and the Sun have similar compositions, chondrites are thought to have very primitive...

Faultblock mountains

Fault-block mountains generally form by extension of the continental crust. The best examples include the Basin and Range Province of the western United States, and parts of the East African Rift System, including the Ethiopian Afar. These mountain belts are formed by the extension or pulling apart of the continental crust, forming basins between individual tilted fault-block mountains. These types of ranges are associated with thinning of the continental crust, and some have active volcanism...

Formation Of Solar System

South America Map

The solar system began to form from a spinning solar nebula about 5 billion years ago, 9 billion years after the universe started expanding from nothing in the big bang some 14 billion years before the present. This solar nebula consisted of a mass of gas, dust, and fragments that began spinning faster as gravitational forces caused the material to collapse on itself. Temperatures ranged from extremely hot in inner parts of the solar nebula to cold in the outer reaches. Planets began accreting...

Further Reading

Turcotte, Donald L., and Gerald Schubert. Geodynamics. 2nd ed. Cambridge Cambridge University Press, 2002. geographic information systems (GiS) Geographic information systems (Gis) are computer application programs that organize and link information to enable users to manipulate that information constructively. They typically integrate a database management system with a graphics display that shows links between different types of data. For instance, a Gis may show relationships among...

Glaciated Coasts

Glaciated and recently deglaciated coastlines offer a variety of environments that are significantly different from other coastal features so far discussed. some coastlines, such as many in Antarctica, Greenland, and Alaska, have active glaciers that reach the sea, whereas other coasts, such as from New England northward into Canada, scandinavia, and parts of the Far East have recently been deglaciated (within the past 18,000 years). The primary effects of glaciers on coastlines include the...

Nuclear Attack

One of the most popular ideas for deflecting asteroids away from a potential collision with Earth is to fire many nuclear missiles at the asteroid, with the idea that the blast would vaporize the asteroid, eliminating the danger. However, the energy requirements may not be attainable with the world's current arsenal of nuclear weapons, as there are currently no nuclear weapons that release enough energy to destroy an asteroid only a half mile (1 km) in diameter. If enough blasts or a large...

Mozambique

In 1911 Holmes obtained a position as a geological prospector for Memba Minerals Limited. After giving his research results to Strutt, Holmes left England for Mozambique in March, beginning a physically difficult six-month expedition in search of economically valuable minerals. While there, Holmes contracted malaria, and high fevers occasionally forced him to rest for several days. Lying in bed, he could not stop thinking about radiometric dating and contemplated how he could reconcile data...

Summary

Streams are dynamic systems that represent a balance between the forces that drive the current and those that resist the flow. Channels have many different styles that form in response to a quasi equilibrium between the gradient, or slope, of the streambed, the discharge of the stream, the amount of sediment being transported, the roughness of the streambed, and the resistance of the bank to erosion. The stream may form one of three main types of channels in response to the relative...

Solar Atmosphere

The lower part of the solar atmosphere, resting directly above the photosphere, is called the chromosphere. The chromosphere emits very little light compared to the photosphere, so is visible only during total solar eclipses, as a bright and somewhat irregular diffuse band around the Sun. The chromosphere has relatively few gas particles (hydrogen), so emits few photons. However, the chromosphere is a dynamic environment. Every few minutes the convection cells on the surface of the Sun emit...

The Seashell Question

Thomas Bartholin, an anatomy professor from the university of Copenhagen, was famous for his discovery of the vessels that carry lymph throughout the body. Lymph is a transparent, yellowish fluid that plays an important role in the immune system and in the transportation of certain materials throughout the body. Bartholin not only conveyed an appreciation for anatomy to steno but introduced the famous seashell question to him. In mountainous regions, objects which resembled seashells and other...

Theory Of The Earth

On March 7, 1785, Hutton was to read his paper, Theory of the Earth or an Investigation of the Laws Observable in the Composition, Dissolution, and Restoration of Land upon the Globe to the newly chartered Royal Society of Edinburgh. But he became overly nervous from anticipation and the task fell to his friend Joseph Black. He had recovered by the next meeting on April 4, when he read the remainder of his paper. At the time the prevailing theory for the Earth's formation emphasized the...

Water As A Resource

Since freshwater is essential for life, it may be considered an economic resource to manage effectively. Water is needed for drinking, irrigation, household, recreational, and industrial applications. In the United States agriculture uses about 43 percent of all water resources, and industry uses another 38 percent. On a global scale irrigation for agriculture accounts for an even higher percentage of water use, an estimated 69 percent of total water consumption, whereas industry uses only...

Water as a hazard

While the supply of clean freshwater is barely able to meet present demands and is expected to become a bigger problem, sometimes there is too much water in one place at one time, creating hazards of another kind. When rains, heavy snowmelts, or combinations of these events bring more water than normal into populated areas, floods result. Many floods cause significant damage and destruction because over the past couple of centuries many cultures have moved large segments of their populations...

Galactic Evolution

Despite years of research, there is still remarkably little known about the processes of galaxy formation and why there is such variety in the structure of different galaxies. Most astronomers suggest that small density fluctuations in the primordial matter led to the formation of many small pregalactic masses that were similar to present-day dwarf galaxies, and that collisions and mergers of these galaxies led to the formation of the larger galaxies common in the pres ent universe. As the...

Geomagnetism geomagnetic reversal

Severity of such destructive natural events reduces their consequences significantly. Communities can use this information to plan evacuations, strengthen buildings, and make detailed plans of what needs to be done in natural disasters to such a degree that their costs have been greatly reduced. Increased government responsibility accompanies this greater understanding. Formerly society hardly looked to government for aid in natural disasters. For instance, nearly 10,000 people perished in a...

Electromagnetic Radiation

The electromagnetic spectrum categorizes types of radiation according to wavelength, with the shortest wavelengths being cosmic rays, and in increasing wavelength, gamma rays, X-rays, ultraviolet rays, visible rays, infrared rays, microwave rays, radio waves, and television waves. The environment contains a low level of constant background radiation, mostly from the radioactive decay of minerals and radioactive gases such as radon and thoron. Some background radiation, known as cosmic...

Regional Flood Disasters

Some flooding events are massive, covering with water hundreds of thousands of acres along the entire floodplain of a river system. These floods tend to rise slowly and may have high water for weeks or even months. History has shown that many levees fail during regional long-term flooding events, because most levees are designed to hold back high water for only a short time. The longer the water remains high, the more the water pressure acts on the levee, slowly forcing the water into the...

Supernova Remnants

Supernovas are observed only about every hundred years from Earth, but many supernova remnants are still observable long after their peak of luminosity and radiance. The most famous of these is the Crab Nebula, now a dim nebula sitting about 5,940 light-years (1,800 parsecs) from the Earth and having a visible angular diameter about one-fifth that of the Moon. The Crab Nebula is so interesting because in 1054 its initial explosion was recorded by Chinese, Native American, and Middle Eastern...

Later scientific contributions

In 1908 Einstein finally received an academic position at the University of Bern, which gave him the title privatdozent (roughly equivalent to a postdoctoral researcher, granted by some European universities for those who hold a Ph.D. and Habilitation and want to pursue an academic career). Einstein published a paper in 1910 on critical opalescence, describing how light is scattered by molecules in the atmosphere, making the sky appear blue. He also worked more on the quantization of light,...

The Problem With Lead

In 1912 Imperial College offered Holmes a position as a demonstrator in geology, and in July 1914 the 23-year-old geologist married Margaret Howe. Holmes kept busy lecturing and researching the pet-rographical material he brought back from Mozambique. When World War I broke out in August, the military declared Holmes unfit for military service because of his recurring bouts of malaria. His contributions toward the war effort included making scaled topography maps for naval intelligence and...

Scientific ContnBUTIONS

After completing his studies, Nicolaus Copernicus returned to Prussia and took on the position of secretary to his uncle Lucas Watzenrode, who was at the time the bishop of Warmia. During this time he lived at the bishop's castle at Lidzbark Warminski (Heilsberg) and started his research on the heliocentric model of the universe. Copernicus obtained a position as a burgher of Warmia in the Collegiate Church of the Holy Cross in Wroclaw (Breslau) in Bohemia, and he kept this position for most of...

Cretaceoustertiary Boundary And The Cenozoic

The Cenozoic Era marks the emergence of the modern Earth, starting at 66 million years ago and continuing until the present. The Cenozoic includes the Tertiary (Paleogene and Neogene) and Quaternary Periods, and the Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and Holocene Epochs. Many modern ecosystems developed in the Ceno-zoic, with the appearance of mammals, advanced mollusks, birds, modern snakes, frogs, and angio-sperms such as grasses and flowering weeds. Mammals...

Ground Motion

How Tectonic Plates Leads Landslides

One of the primary hazards of earthquakes is ground motion caused by the passage of seismic waves through populated areas. The most destructive waves Collapsed 10-story apartment building in Islamabad, Pakistan, after earthquake October 8, 2005 The building pancaked as one floor fell, thereby causing each lower floor to collapse. (AP images) Damage from ground shaking and landslides in Yingxiu, Sichuan Province, China, from May 12, 2008, magnitude 7.9 earthquake (T. Kusky) are surface waves,...

Haiti 2010 magnitude

On Tuesday, January 10, 2010, at 4 53 p.m., Port-au-Prince, the capital city of Haiti, was hit by a magnitude 7.0 earthquake that essentially leveled the city, killing an estimated 200,000 people and severely affecting another 3 million. As of January 31, 2010, about 150,000 bodies had been recovered, but of necessity many were dumped in mass graves outside the capital, so exact estimates of the number of people killed may never be known. Cities and towns outside the capital, such as Jacmel,...

Tsunami Hazard zones and Risk Mapping

The USGS and other Civil Defense agencies have mapped many areas that are particularly prone to tsunamis. Recent tsunamis, historical records, and deposits of ancient tsunamis identify some of these areas. Many coastal communities, especially those in Hawaii, have posted coastal areas with tsunami warning systems, showing maps of specific areas prone to tsunami inundation. Tsunami warning signals are in place and residents are told what to do and where to go if the alarms are sounded. Residents...

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Alfred Wegener with pipe and parka (Alfred-Wegener-Institut, Germany) and Africa lined up if the continents were once together, and belts of distinctive rock types, such as coal, also matched on different continents if they were restored to his hypothesized supercontinent of Pangaea (meaning all land). Alfred Wegener studied the fossils and found that narrow belts of distinctive fauna and flora, such as the reptiles Mesosaurus and Lystrosaurus, matched on the former supercontinent and that the...

Glossary

Abrasion a process that occurs when particles of sand and other sizes are blown by the wind and impact each other absorption in physics and astronomy, the process where energy from a photon is taken up by matter, typically electrons of an atom, and converted into some other form of energy (typically heat), causing reduction of light from a distant source. An absorption line is a dark line in an otherwise continuous spectrum, where the light from one narrow frequency range has been removed by...

Forerunner

Impressed, the grand duke granted him a salary, and Steno became a full member of the Cimento. He was able to explore fully his new geological interests with all expenses paid. He traveled around Tuscany collecting fossils, climbing mountains, and examining strata. He also continued dabbling in anatomy and arrived at a startling conclusion during this time. It was obvious that females of many species of animals laid eggs, but Steno proved that females that gave birth to live organisms also...

China

China contains some of the most complex geology in the world, ranging from a number of ancient Archean cratons, to active tectonic belts, and offshore marine basins. The geomorphology changes from deep marine basins, to coastal plains, flat steppes, deserts, mountains, and the highest plateau of uplifted crust in the world. With such diversity it is fortunate that China has a long history of geological exploration and records, although much of this is not easily accessible to the Western world....

Active Faulting Of Lake Alaotra Central Madagascar

The Lake Alaotra-Ankay rift valley of central Madagascar forms a roughly northeast-southwest oriented depression that is filled with Neogene to Recent sediments, and is part of a more regional post-Miocene graben system that strikes north-south across much of the central part of the island. The region is characterized by a number of small earthquakes, steep fault-scarp bound valleys, several levels of terraces, and deeply incised topography related to intense tropical weathering. The origin and...

Wyoming and Churchill Cratons

The Wyoming craton is exposed discontinuously in the Laramide ranges of Wyoming and Montana. Rocks in the province include abundant shelf-type metasedimentary rocks, including quartzite, marble, and pelite, and older crust consisting of 3.6 to 3.1 billion-year-old granulites and gneisses. The rocks have been complexly folded and sheared, making correlations difficult, but most seem to have been deformed and assembled between 2.9 and 2.6 billion years ago. A late Archean suture has been...

Comets And The Origins Of Life

Comets are rich in water, carbon, nitrogen, and complex organic molecules that originate deep in space from radiation-induced chemical processes. Many of the organic molecules in the coma of comets originated in the dust of the solar nebula at the time and location where the comets initially formed in the early history of the solar system. Comets are relatively small bodies that have preserved these early organic molecules in a cold, relatively pristine state. This has led many scientists to...

Origin Of Life

The Earth is believed to be unique in the solar system in that it supports life, yet how life appeared is still unknown. A popular model for the origin of life was formulated in the 1920s. This model suggests that life originated as a consequence of chemical reactions on the early, nonliving Earth. The planet naturally contains a lot of carbon, hydrogen, oxygen, and nitrogen, the major building blocks for life in most organisms. Water is a universal solvent, and early ideas for the origin of...

Tsunamis and Seiche Waves

Several types of large waves are associated with earthquakes, including tsunamis and seiche waves. Tsunamis, also known as seismic sea waves, form most usually from submarine landslides that displace a large volume of rock and sediment on the seafloor, which in turn displaces a large amount of water. Tsunamis may be particularly destructive as they travel very rapidly (hundreds of miles per hour), and may reach many tens of yards above normal high-tide levels. The most devastating tsunami in...

Historical Development Of The Plate Tectonic Paradigm

India Asia Collision Tectonic

The plate tectonic paradigm was developed from a number of different models, ideas and observations that were advanced over the prior century by a number of scientists on different continents. Between 1912 and 1925, Alfred Wegener, a German meteorologist, published a series of papers and books outlining his ideas for the evolution of continents and oceans. Wegener was an early proponent of continental drift. He looked for a driving mechanism to move continents through the mantle, and invoked an...

Eskola Pentti 18831964 Finnish Geologist

Pentti Eelis Eskola was born in Lellained, Finland, to a farming family. After growing up on the farm he studied at the university of Helsinki, then in 1922 moved to the Carnegie Institution in Washington, D.C., for a postdoctoral position where he conducted experimental studies on the chemical behavior of rock and mineral systems. After two years in Washington Eskola moved back to the university of Helsinki, where he became a chemist before specializing in petrology. He remained a professor...

Global Firestorm and Global Winter

The force of large- and medium-scale impacts ejects enormous quantities of superheated dust and gases into the atmosphere, some of which would fall back to Earth as flaming fireballs. Most of the dust would make it into the upper atmosphere, where it would encircle the entire planet. The energy from the impact would heat the atmosphere to such a degree that it would spontaneously ignite forests and much of the biomass, sending dark clouds of smoke into the atmosphere. This smoke and the dust...

Caledonides

The Caledonides are an early Paleozoic orogenic belt in north and east Greenland, scandinavia, and the northern British Isles. The Caledonides were continuous with the Appalachian Mountains before the opening of the Atlantic Ocean, together extending more than 4,101 miles (6,600 km). The history of the opening and closing of the Early Paleozoic Iape-tus Ocean and the Tornquist Sea is preserved in the Caledonian-Appalachian orogen, which is one of the best-known and studied Paleozoic orogenic...

Early Years

Harry Hammond Hess was born on May 24, 1906, in New York City, to Julian and Elizabeth Engel Hess. His father worked at the New York Stock Exchange. Harry had one brother, Frank. When he was five Harry's parents photographed him in a sailor suit and fittingly titled the portrait The Little Admiral, foreshadowing Harry's career. He attended Asbury Park High School in New Jersey, where he specialized in foreign languages. In 1923 Hess enrolled at Yale University, where he planned to major in...

Sealevel Changes Related To Changes in continental AREA

Continent-continent collisions can lower sea levels by reducing the area of the continents. When continents collide, mountains and plateaus are uplifted, and the amount of material that is taken from below sea level to higher elevations no longer displaces seawater, causing sea levels to drop. The ongoing India-Asia collision has caused sea levels to drop by 33 feet (10 m). other things, such as mid-plate volcanism, can also change sea levels. The Hawaiian islands are hot-spot style mid-plate...

The Sun And Changes In ExTernalenergy Caused By Orbital Variations

The Sun is the main external contributor of energy to the Earth. The amount of radiation emitted by the Sun is nearly constant on human timescales, but solar emissions vary on 1,500-year timescales. Variations in Earth's orbital parameters around the Sun cause other more significant and systematic changes in the amount of incoming solar radiation. These changes can affect many Earth systems, causing glaciations, global warming, and changes in the patterns of climate and sedimentation. Radiant...

Baltic Shield and Caledonides on Svalbard and Spitzbergen Island

Spitzbergen is the largest island (15,000 square miles 40,000 km2) of Svalbard, a large island territory of Norway located in the Arctic Ocean. The islands are on the Barents Shelf, bounded by the Greenland Sea on the west and the Arctic Ocean on the north. The entire Svalbard archipelago was originally referred to as Spitzbergen, but in 1940 the name was changed to Svalbard, and Spitzbergen was reserved for the largest island of the archipelago that also includes the islands of Nordaustlandet,...

Influence Of Shortterm Climate Changes On Sea level

Minor changes in sea level of up to about a foot (30 cm) happen in many places in yearly seasonal cycles. Many of these are caused by changes in the wind patterns, as the sun alternately heats different belts of the ocean, and the winds blow water from one side of the ocean to the other. When water is heated in the summer months it also expands slightly, accounting for sea-level changes of an inch (2.5 cm) or so. Thermal expansion associated with global warming may raise sea levels about 12...

Controls of deformation

Deformation of the lithosphere is controlled by the strength of rocks, which in turn depends mostly on temperature and pressure. strength increases with pressure and decreases exponentially with increasing temperature. Because temperature and pressure both increase downward, a cross section through the crust or lithosphere will have different zones where the effects of either pressure or temperature dominate. In the upper layers of the crust, effects of pressure dominate, and rocks that are...

Oceans And Climate

The compositions of the Earth's early atmospheres and oceans are not well known, but most models fall into two groups. One is that the early atmosphere was relatively oxygen free (anaerobic), and the other, that it was aerobic, or had oxygen levels approaching modern values. The early anaerobic atmosphere-ocean model was suggested by biochemists to support their model for the origin of life. This is supported by many dark-colored Archean sedimentary rocks that contain unoxidized carbon, iron...

Unconformities And Gaps In The HistonCal Geological record

Unconformities are regional surfaces that extend for large distances and represent periods of time missing from the geological record at that location. To interpret unconformities and understand what each means for the history of the region and Earth, it is important to determine how much of a time gap is represented, and what caused the stratum that would have been deposited in that interval to not be preserved. In some cases the stratum was once there and has since been eroded, and in other...

Relative ages of strata

Biostratigraphy is the branch of stratigraphy that uses fossil assemblages and index fossils to correlate and assign relative ages to strata. Index fossils are used to identify and define geological periods, or faunal stages. Ideal index fossils are short-lived, have a broad distribution, and are easy to identify. Most good index fossils are floating or swimming organisms that live independently of the bottom environment. Many have floating larval stages that are dispersed by currents, seeds or...

Fold and thrust belts

Fold and thrust mountain chains are contractional features, formed when two tectonic plates collide, forming great thrust faults and folding metamorphic rocks and volcanic rocks. By examining and mapping the structure in the belts we can reconstruct their history and essentially pull them back apart in the reverse of the sequence in which they formed. By reconstructing the history of mountain belts in this way, we find that many of the rocks in the belts were deposited on the bottom of the...

DRY valleys Of Antarctica

The Dry Valleys are the largest area on Antarctica not covered by ice. Approximately 98 percent of the continent is covered by ice, but the Dry Valleys, located near McMurdo Sound on the side of the continent closest to New Zealand, have a cold desert climate and receive only four inches (10 cm) of precipitation per year, overwhelmingly in the form of snow. The Dry Valleys are one of the coldest, driest places on Earth and are used by researchers from NASA as an analog for conditions on Mars....

Causes Of Changing Sea Levels

The average position of the median sea level may appear to rise or fall with respect to the land surface to an observer on a shoreline, and this is called relative sea-level rise or fall. However, it is difficult for the observer on the local shoreline to know if the height of the water is changing, or if the height of the continent is rising or falling. In many places plate tectonics causes areas of the crust to rise slowly out of the sea or to sink gradually downward below sea level, while...

Modifications And Channelization Of RivEr Systems To Alleviate Water Shortages

Some desert and semiarid regions of the world have undergone rapid population explosions, necessitating the alteration of river courses to bring water to thirsty cities and to provide irrigation to farmlands to feed this growing population. In the American desert southwest, California, and the middle East, riverways have been extensively modified, regulated, and sometimes diverted hundreds of miles from their Population curve showing the number of humans on Earth natural course to provide water...

Siluriandevonian 436360 Million Years Ago History Of Life

Reducing Tectonic Risk

In the Silurian and Devonian, organisms continued to evolve rapidly in the shallow sea that covered much of the continent, and like the late Ordovician, brachiopods and bryozoans were the most common organisms in the shallow seas. However, echinoderms became increasingly more important and abundant in the Silurian. By Silurian times the nautiloids and cephalopods had nearly disappeared, and the grapto- lites were virtually extinct. One line of descent of the nautiloids survived and evolved into...

Storm Surges and Bangladesh

The area that seems to be hit by the most frequent and most destructive storm surges is Bangladesh. A densely populated, low-lying country, Bangladesh sits mostly at or near sea level between India and Myanmar. It is a delta environment, built where the Ganges and Brahmaputra Rivers drop their sediment eroded from the Himalaya Mountains. Bangladesh is frequently flooded from high river levels, with up to 20 percent of the low-lying country being under water in any year. It also sits directly in...

Formation Of Glaciers

Glaciers form mainly by the accumulation and compaction of snow, and are deformed by flow under the influence of gravity. When snow falls it is porous, and with time the pore spaces close by precipitation and compaction. When snow first falls, it has a density of about 1 10th that of ice after a year or more the density is transitional between snow and ice, and it is called firn. After several years the ice reaches a density of 0.9 g cm3, and it flows under the force of gravity. At this point...

Sealevel Changes Related To Changes In Midocean Ridge Volume

Sea levels may change at different rates and amounts in response to changes in several other Earth systems. Local tectonic effects may mimic sea-level changes through regional subsidence or uplift, and these effects must be taken into account and filtered out when trying to deduce ancient, global (eustatic) sea-level changes. The global volume of the mid-ocean ridges can change dramatically, either by increasing the total length of ridges, or changing the rate of seafloor spreading. The total...

Gravity gravity anomaly Gravity is the attraction between any body in the universe and all other bodies described by

Where F represents the force of gravity, M represents the masses of the two bodies that are attracted, and r represents the distance between the objects. Often the term gravity refers specifically to the force exerted on any body on or near the surface of the Earth by the mass of the Earth and any centrifugal force resulting from the planet's rotation. A gravity anomaly is the difference between the observed value of gravity at a point and the theoretically calculated value of gravity at that...

Ekman Spirals

Ekman spirals are differences in current directions with depth, and form through the turning of water with depth as a result of the Coriolis force. They form because each (infinitesimally thin) layer of the ocean water exerts a frictional drag on the layer below, so that as the top layer moves, the layers below move slightly less with each depth increment. Because the Coriolis force causes moving objects to deflect to the right in the Northern Hemisphere and to the left in the Southern...

Water Politics and the Middle East

Tectonic Plate Boundaries Grid

Water shortage, or drought, coupled with rapid population growth provides for extreme volatility in any region. In the Middle East water shortage issues are coupled with long-standing political and religious differences. The Middle East, stretching from North Africa and the Arabian Peninsula, through Israel and Lebanon to Turkey, and along the Tigris-Euphrates valleys, has only three major river systems and a few smaller rivers. The population stands at about 160 million. The Nile has an annual...

Gravitational Tractor Strategies

Many asteroids and comets are composed of piles of disconnected rubble. Deflection strategies that rely on kinetic impact or deflection by explosion would not necessarily work on these types of asteroids, since any impact would only deflect the fragment that it directly hit. One alternative type of deflection strategy involves slowly moving these asteroid rubble piles by moving a massive spacecraft near the asteroid and letting the gravitational attraction of the spacecraft slowly pull the...

Platinum Group Elements

Some rare metals known as platinum group elements (PGEs) form economic concentrations in some ultra-mafic igneous rocks and take several forms. Chro-mite may occur as layers, typically in continental intrusions or as small pods in ultramafic rock associations. Chromite and platinum group elements are typically associated with sulfide minerals and form when there is enough sulfur in the magma to crystallize these phases while the rock is still in liquid forms. In many cases the metal phases are...

Classification Of Rock Units

The layered rocks in the Arabian shield are classified into three major rock units, each of them belonging to one of the three tectonic cycles mentioned above. These major layered rock units are the lower, middle, and upper layered rock units. The lower layered rock unit covers those rock groups that formed in the early upper Proterozoic tectonic cycle (older than 800 Ma) and includes rocks with continental affinity. The volcanic rocks that belong to this unit are characterized by tholei-itic...

Braided river channel and alluvial terraces on Golmud River in the Kunlun Mountains Qinghai Province China Fletcher

Geomorphology represent a significant movement away from classical geomorphology, which is concerned mostly with the evolutionary development of landforms. Geomorphological phenomena depend on many different processes that operate on the surface of the planet, so the geomorphologist needs to integrate hydrology, climate, sedimentology, geology, forestry, pedology, and many other sciences. This type of research has relevant applications to everyday life for example, the decomposition of bedrock...

Discovery Of A Sauvary Duct

During his studies steno was examining the arteries and veins surrounding the jaws on a butchered sheep head and inserted his skinny metal probe through a small tunnel and heard a clinking noise from hitting teeth. After close examination, he realized he had discovered a previously unrecognized duct leading from the parotid gland to the oral cavity. The parotid glands supply saliva to the mouth. he pointed this out to his teacher. Blaes immediately cast off steno's finding as a blunder. he...

Predicting future earthquakes in the western united states

The Earth is a dynamic planet composed of different internal layers that are in constant motion, driven by a vast heat engine deep in the planet's interior. The cool surface layer is broken into dozens of rigid tectonic plates that move around on the surface at rates of up to a few inches ( 5 cm) per year, driven by forces from the internal heat and motion in the partly molten layers within the planet. Most destructive earthquakes are associated with motions of continents and ocean floor rocks...

The Mid Ocean Ridge Is Approximately 75000 Miles Long

Knapp, A. Perez-Estaun, T. Hismatulin, N. Yunusov, and A. Lipilin. Orogenic Evolution of the Ural Mountains Results from an Integrated Seismic Experiment. Science 274 (1996) 220-221. Bogdanova, Svetlana V., R. Gorbatschev, and R. G. Garetsky. The East European Craton. In Encyclopedia of Geology, vol. 5, edited by R. C. Selley, L. R. Cocks, and I. R. Plimer, 34-49. Amsterdam London Elsevier Academic, 2005. Condie, Kent C., and Robert Sloan. Origin and Evolution of...

Pangaea

The Late Paleozoic saw the formation of Pangaea, which included the southern continents amassed in Gondwana and the northern continents grouped in Laurasia. Most of the evidence for the formation of the supercontinent of Pangaea comes from the southern continents, since nearly all of these contain nearly identical fossils and stratigraphy. These were studied extensively by Alex Du Toit from south Africa, and Alfred Wegener from Germany. Separately these two scientists pieced together evidence...

Granulitegneiss Belts

High-grade granitoid gneiss terrains form the second main type of Archean terrain. Examples include the Limpopo belt of southern Africa, the Lewisian of the North Atlantic Province, the Hengshan of north China, and some less-well-documented belts in Siberia and Antarctica. The high-grade gneiss assemblage seems similar in many ways to the lower-grade greenstone belts, but more strongly deformed and metamorphosed, reflecting burial to 12.5-25 miles (20-40 km) depth. Strongly deformed mylonitic...

Geographic information systems

Magma through subvolcanic feeder systems and in lava tubes, flow of material into (and out of) subduction zones, as well for understanding mantle flow associated with glacial rebound. Thermal convection is modeled in fluid dynamics and has obvious applications to mantle convection, the driving forces of plate tectonics, and also to systems such as modeling fluid flow around hot springs, submarine black smoker chimneys, and geological mineral deposits formed by circulating hot fluids....

Divergent Plate Boundaries And The Creation Of Oceanic Crust

Where plates diverge, seafloor spreading produces new oceanic crust. As the plates move apart, the pressure on deep underlying rocks decreases, which causes them to rise and partially melt by 15-25 per cent. Basaltic magma is produced by partially melting the peridotitic mantle, leaving a residue type of rock in the mantle known as harzburgite. The magma produced in this way upwells from deep within the mantle to fill the gap opened by the diverging plates. This magma forms a chamber of molten...

Archean

In the Archean the surface of the planet looked very different than it does now. Life was limited to primitive bacteria, so the land had no vegetative cover. The Earth was also producing more heat in the Archean than it is now, so it is likely that heat loss mechanisms, particularly plate tectonics, were operating much more vigorously then than now, with more seafloor volcanism, perhaps greater ridge length, and faster plate motion. Precambrian rocks form about 50 percent of the continental...

The large hadron collider

Physicists go to extreme lengths to solve some of the deepest mysteries of the universe. The Large Hadron Collider (LHC) is a huge, 16.7-mile- (27-km-) long ring containing 9,300 superconducting magnets buried 109 yards (100 m) underground near Geneva, crossing the border between Switzerland and France. It is the world's largest particle accelerator (and the largest machine of any type in the world), designed to study the smallest known particles that are the building blocks of all things. The...

Flash Floods in the Northern Oman Mountains

The Northern Oman (Hajar) Mountains are a steep, rugged mountain range on the northeastern Arabian Peninsula, with deep, long canyons that empty into the Gulf of Oman and the Arabian Sea. These are normally dry canyons or wadis, and the local villagers dig wells in the wadi bottoms to reach the groundwater table for use in homes and agriculture. The region is normally very dry, but infrequent thunderstorms grow and explode over parts of the mountains. Occasionally a typhoon works its way from...

Copper Deposits

Most economic copper deposits are found in association with volcanic-plutonic arc sequences in porphyry copper deposits, but other economic resources of copper are known from sedimentary deposits. In porphyry copper deposits the copper is carried by the sulfide mineral chalcopyrite, which is enriched and carried upward by the granitic magmas and by hydrothermal fluids associated with the plutons. Copper is also often found in association with nickel, gold, lead, and zinc deposits. Copper can...

Urbanization and Changes in the Missouri river Floodplain

The Missouri River stretches more than 2,300 miles and drains one-sixth of the united states. It was once one of the wildest stretches of rivers in the American Midwest. During the past two centuries the Missouri, along with its adjacent wetlands and floodplains, has been dramatically modified in various attempts to promote transportation, agriculture, and development. These modifications have included draining wetlands for cultivation, straightening stream channels to facilitate navigation,...

Magma Composition And Naming Igneous Rocks

Determining whether an igneous rock is phaneritic or aphanitic is just the first stage in giving it a name. The second stage is determining its chemical com Fountaining and lava flow from Pu'u O eruption of Kilauea, Hawaii, January 31, 1984 (J.D. Griggs, USGS) ponents. The composition of magma is controlled by the most abundant elements in the Earth, including silicon (Si), aluminum (Al), iron (Fe), calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), hydrogen (H), and oxygen (O). Oxygen...

Tsunami Warning Systems

Tsunami warning systems have been developed that are capable of saving many lives by alerting residents of coastal areas that a tsunami is approaching their location. These systems are most effective for areas located more than 500 miles (750 km), or one hour away from the source region of the tsunami, but may also prove effective at saving lives in closer areas. The tsunami warning system operating in the Pacific ocean basin integrates data from several different sources, and involves several...

Lunar Impact Craters

The Earth's Moon is the closest celestial object, and it is covered by many impact craters, large and small. The lack of water, crustal recycling through plate tectonics, and weathering as on Earth has preserved craters that are billions of years old, providing scientists with a natural laboratory to observe and model impact craters of different sizes and styles. Thousands on thousands of photographs have revealed the great diversity in styles of lunar craters and have yielded insight into the...

Stony Iron Meteorites

As the name implies, stony-iron meteorites consist of mixtures of metal and silicate (rocky) components, resembling a cross between achondrites and iron meteorites. They are thought to come from the part of a planetesimal or parent body near the boundary of the core and mantle, incorporating parts of each in the meteorite. Stony-iron meteorites are classified into pallas-ites and mesosiderites. Pallasites contain a mixture of Widmannstatten-textured iron phases and large yellow to green olivine...

Introduction

Folding Faulting Making Things

Encyclopedia of Earth and Space Science is a two-volume reference intended to complement the material typically taught in high school Earth science and astronomy classes, and in introductory college geology, atmospheric sciences, and astrophysics courses. The substance reflects the fundamental concepts and principles that underlie the content standards for Earth and space science identified by the National Committee on Science Education Standards and Assessment of the National Research Council...

Divergent plate boundaries in continents

Brittle Ductile Transition

Rifts are elongate depressions formed where the entire thickness of the lithosphere has ruptured in extension. In these places the continents are beginning to break apart as immature divergent boundaries, and if successful, may form new ocean basins. The general geomorphic feature that initially forms is known as a rift valley. Rift valleys have steep, fault-bounded sides, with rift shoulders that typically tilt slightly away from the rift valley floor. Drainage systems tend to be short,...

Foreland Basins

Foreland basins are wedge-shaped sedimentary basins that form on the continentward side of fold-thrust belts, filling the topographic depression created by the weight of the mountain belt. Most foreland basins have asymmetric, broadly wedge-shaped pro files with the deeper side located toward the mountain range, and a flexural bulge developed about 90 miles (150 km) from the foothills of the mountains where the deformation front is located. The indo-Gangetic plain on the south side of the...

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...

Tectonic Setting Of 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...