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...

Proterozoic

The Proterozoic rock record shows many features that suggest that large continents were present in this interval, including the first appearance in the geological record of very thick and abundant mature quartz sandstones, although some smaller examples are known from the Archean. These sedimentary rocks include well-sorted quartzites and quartz-rich graywackes, and indicate long periods of abrasion on stable continental shelves, and in some cases are depositionally related to abundant...

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...

Further Reading

Origin and Evolution of Earth, Principles of Historical Geology. upper saddle River, N.J. Prentice Hall, 1997. Windley, Brian F. The Evolving Continents. 3rd ed. Chichester, England John Wiley & sons, 1995. Paleolithic The Paleolithic is the first division of the stone Age in archaeological time, marked by the first appearance of humans and their associated tools and workings. The time of the Paleolithic corresponds generally with the Pleistocene (from 1.8...

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

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

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...

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...

Precession Nutation

Precession Nutation

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

Plate Tectonics Climate

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...

Summary

Modern classification schemes for the composition of asteroids and meteorites divide them into either chondrites or nonchondrites. The nonchondrites are divided into primitive and differentiated types. The differentiated nonchondrites have three groups, including the achondrites, stony-irons, and irons, based on the chemistry and texture of the meteorites and reflecting their origin. Chondrites have compositions similar to the sun, and represent the average composition of the solar system,...

Andes Tectonic Zonation

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...