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59-991: The National Geophysical Research Institute ( NGRI ) is a geoscientific research organization established in 1961 under the Council of Scientific and Industrial Research (CSIR), India's largest Research and Development organization. It is supported by more than 200 scientists and other technical staff whose research activities are published in several journals of national and international interest. Research areas covered by this institute include hydrocarbon and coal exploration, mineral exploration, deep seismic sounding studies, exploration and management of groundwater resources, earthquake hazard assessment, structure of Earth's interior and its evolution (theoretical studies), geophysical instrument development and geothermal exploration. The major facilities available at NGRI include: This article about an organisation in India

118-405: A base or reference level h b {\displaystyle h_{b}} , the depth of the ocean d ( t ) {\displaystyle d(t)} is of interest. Because d ( t ) + h ( t ) = h b {\displaystyle d(t)+h(t)=h_{b}} (with h b {\displaystyle h_{b}} measured from

177-586: A constant temperature T 1 . Due to its continuous creation, the lithosphere at x > 0 is moving away from the ridge at a constant velocity v , which is assumed large compared to other typical scales in the problem. The temperature at the upper boundary of the lithosphere ( z = 0) is a constant T 0 = 0. Thus at x = 0 the temperature is the Heaviside step function T 1 ⋅ Θ ( − z ) {\displaystyle T_{1}\cdot \Theta (-z)} . The system

236-591: A failed arm that was opening more slowly than the other two arms, but in 2005 the Ethiopian Afar Geophysical Lithospheric Experiment reported that in the Afar region , September 2005, a 60 km fissure opened as wide as eight meters. During this period of initial flooding the new sea is sensitive to changes in climate and eustasy . As a result, the new sea will evaporate (partially or completely) several times before

295-586: A field of a magnetic dipole currently tilted at an angle of about 11° with respect to Earth's rotational axis, as if there were an enormous bar magnet placed at that angle through the center of Earth. The North geomagnetic pole ( Ellesmere Island , Nunavut , Canada) actually represents the South pole of Earth's magnetic field, and conversely the South geomagnetic pole corresponds to the north pole of Earth's magnetic field (because opposite magnetic poles attract and

354-482: A hypothesis of continental drift in 1912, he suggested that continents plowed through the ocean crust. This was impossible: oceanic crust is both more dense and more rigid than continental crust. Accordingly, Wegener's theory wasn't taken very seriously, especially in the United States. At first the driving force for spreading was argued to be convection currents in the mantle. Since then, it has been shown that

413-413: A mid-ocean ridge is the spreading half-rate and is equal to half of the spreading rate). Spreading rates determine if the ridge is fast, intermediate, or slow. As a general rule, fast ridges have spreading (opening) rates of more than 90 mm/year. Intermediate ridges have a spreading rate of 40–90 mm/year while slow spreading ridges have a rate less than 40 mm/year. The highest known rate

472-518: Is a stub . You can help Misplaced Pages by expanding it . Geoscientific Geology is broadly the study of Earth's structure, substance, and processes. Geology is largely the study of the lithosphere , or Earth's surface, including the crust and rocks . It includes the physical characteristics and processes that occur in the lithosphere as well as how they are affected by geothermal energy . It incorporates aspects of chemistry, physics, and biology as elements of geology interact. Historical geology

531-549: Is assumed to be at a quasi- steady state , so that the temperature distribution is constant in time, i.e. T = T ( x , z ) . {\displaystyle T=T(x,z).} By calculating in the frame of reference of the moving lithosphere (velocity v ), which has spatial coordinate x ′ = x − v t , {\displaystyle x'=x-vt,} T = T ( x ′ , z , t ) . {\displaystyle T=T(x',z,t).} and

590-509: Is brought back into the Earth are convergent boundaries and those where plates slide past each other, but no new lithospheric material is created or destroyed, are referred to as transform (or conservative) boundaries. Earthquakes result from the movement of the lithospheric plates, and they often occur near convergent boundaries where parts of the crust are forced into the earth as part of subduction. Plate tectonics might be thought of as

649-522: Is distinct from human geography , which studies the human populations on Earth, though it does include human effects on the environment. Methodologies vary depending on the nature of the subjects being studied. Studies typically fall into one of three categories: observational, experimental, or theoretical. Earth scientists often conduct sophisticated computer analysis or visit an interesting location to study earth phenomena (e.g. Antarctica or hot spot island chains). A foundational idea in Earth science

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708-402: Is forced into the asthenosphere melts, and some portion of the melted material becomes light enough to rise to the surface—giving birth to volcanoes. Atmospheric science initially developed in the late-19th century as a means to forecast the weather through meteorology , the study of weather. Atmospheric chemistry was developed in the 20th century to measure air pollution and expanded in

767-641: Is forced under either continental crust or oceanic crust. Today, the Atlantic basin is actively spreading at the Mid-Atlantic Ridge . Only a small portion of the oceanic crust produced in the Atlantic is subducted. However, the plates making up the Pacific Ocean are experiencing subduction along many of their boundaries which causes the volcanic activity in what has been termed the Ring of Fire of

826-464: Is formed through volcanic activity and then gradually moves away from the ridge. Earlier theories by Alfred Wegener and Alexander du Toit of continental drift postulated that continents in motion "plowed" through the fixed and immovable seafloor. The idea that the seafloor itself moves and also carries the continents with it as it spreads from a central rift axis was proposed by Harold Hammond Hess from Princeton University and Robert Dietz of

885-477: Is found within the crustal accretion zone. The differences in spreading rates affect not only the geometries of the ridges but also the geochemistry of the basalts that are produced. Since the new oceanic basins are shallower than the old oceanic basins, the total capacity of the world's ocean basins decreases during times of active sea floor spreading. During the opening of the Atlantic Ocean , sea level

944-459: Is generated by electric currents due to the motion of convection currents of a mixture of molten iron and nickel in Earth's outer core : these convection currents are caused by heat escaping from the core, a natural process called a geodynamo . The magnitude of Earth's magnetic field at its surface ranges from 25 to 65 μT (0.25 to 0.65 G). As an approximation, it is represented by

1003-510: Is small compared to L 2 / A {\displaystyle L^{2}/A} , where L is the ocean width (from mid-ocean ridges to continental shelf ) and A is the age of the ocean basin. The effective thermal expansion coefficient α e f f {\displaystyle \alpha _{\mathrm {eff} }} is different from the usual thermal expansion coefficient α {\displaystyle \alpha } due to isostasic effect of

1062-408: Is the application of geology to interpret Earth history and how it has changed over time. Geochemistry studies the chemical components and processes of the Earth. Geophysics studies the physical properties of the Earth. Paleontology studies fossilized biological material in the lithosphere. Planetary geology studies geoscience as it pertains to extraterrestrial bodies. Geomorphology studies

1121-480: Is the density of water. By substituting the parameters by their rough estimates: gives: where the height is in meters and time is in millions of years. To get the dependence on x , one must substitute t = x / v ~ Ax / L , where L is the distance between the ridge to the continental shelf (roughly half the ocean width), and A is the ocean basin age. Rather than height of the ocean floor h ( t ) {\displaystyle h(t)} above

1180-420: Is the notion of uniformitarianism , which states that "ancient geologic features are interpreted by understanding active processes that are readily observed." In other words, any geologic processes at work in the present have operated in the same ways throughout geologic time. This enables those who study Earth history to apply knowledge of how the Earth's processes operate in the present to gain insight into how

1239-441: Is the study of oceans. Hydrogeology is the study of groundwater . It includes the mapping of groundwater supplies and the analysis of groundwater contaminants. Applied hydrogeology seeks to prevent contamination of groundwater and mineral springs and make it available as drinking water . The earliest exploitation of groundwater resources dates back to 3000 BC, and hydrogeology as a science was developed by hydrologists beginning in

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1298-471: The U.S. Naval Electronics Laboratory in San Diego in the 1960s. The phenomenon is known today as plate tectonics . In locations where two plates move apart, at mid-ocean ridges, new seafloor is continually formed during seafloor spreading. Seafloor spreading helps explain continental drift in the theory of plate tectonics . When oceanic plates diverge , tensional stress causes fractures to occur in

1357-399: The cryosphere (corresponding to ice ) as a distinct portion of the hydrosphere and the pedosphere (corresponding to soil ) as an active and intermixed sphere. The following fields of science are generally categorized within the Earth sciences: Seafloor spreading Seafloor spreading , or seafloor spread , is a process that occurs at mid-ocean ridges , where new oceanic crust

1416-424: The heat equation is: where κ {\displaystyle \kappa } is the thermal diffusivity of the mantle lithosphere. Since T depends on x' and t only through the combination x = x ′ + v t , {\displaystyle x=x'+vt,} : Thus: It is assumed that v {\displaystyle v} is large compared to other scales in

1475-403: The lithosphere . The motivating force for seafloor spreading ridges is tectonic plate slab pull at subduction zones , rather than magma pressure, although there is typically significant magma activity at spreading ridges. Plates that are not subducting are driven by gravity sliding off the elevated mid-ocean ridges a process called ridge push . At a spreading center, basaltic magma rises up

1534-460: The solar wind . As the Earth is 4.5 billion years old, it would have lost its atmosphere by now if there were no protective magnetosphere. Earth's magnetic field , also known as the geomagnetic field, is the magnetic field that extends from Earth's interior out into space, where it interacts with the solar wind , a stream of charged particles emanating from the Sun . The magnetic field

1593-427: The 17th century. Ecohydrology is the study of ecological systems in the hydrosphere . It can be divided into the physical study of aquatic ecosystems and the biological study of aquatic organisms. Ecohydrology includes the effects that organisms and aquatic ecosystems have on one another as well as how these ecoystems are affected by humans. Glaciology is the study of the cryosphere, including glaciers and coverage of

1652-515: The 1970s in response to acid rain . Climatology studies the climate and climate change . The troposphere , stratosphere , mesosphere , thermosphere , and exosphere are the five layers which make up Earth's atmosphere. 75% of the mass in the atmosphere is located within the troposphere, the lowest layer. In all, the atmosphere is made up of about 78.0% nitrogen , 20.9% oxygen , and 0.92% argon , and small amounts of other gases including CO 2 and water vapor. Water vapor and CO 2 cause

1711-500: The Earth by ice and snow. Concerns of glaciology include access to glacial freshwater, mitigation of glacial hazards, obtaining resources that exist beneath frozen land, and addressing the effects of climate change on the cryosphere. Ecology is the study of the biosphere . This includes the study of nature and of how living things interact with the Earth and one another and the consequences of that. It considers how living things use resources such as oxygen , water , and nutrients from

1770-425: The Earth to sustain themselves. It also considers how humans and other living creatures cause changes to nature. Physical geography is the study of Earth's systems and how they interact with one another as part of a single self-contained system. It incorporates astronomy, mathematical geography, meteorology, climatology, geology, geomorphology, biology, biogeography, pedology, and soils geography. Physical geography

1829-469: The Earth's atmosphere to catch and hold the Sun's energy through the greenhouse effect . This makes Earth's surface warm enough for liquid water and life. In addition to trapping heat, the atmosphere also protects living organisms by shielding the Earth's surface from cosmic rays . The magnetic field —created by the internal motions of the core—produces the magnetosphere which protects Earth's atmosphere from

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1888-435: The Earth's crust lies the mantle which is heated by the radioactive decay of heavy elements . The mantle is not quite solid and consists of magma which is in a state of semi-perpetual convection . This convection process causes the lithospheric plates to move, albeit slowly. The resulting process is known as plate tectonics. Areas of the crust where new crust is created are called divergent boundaries , those where it

1947-497: The North Pacific): Assuming isostatic equilibrium everywhere beneath the cooling plate yields a revised age depth relationship for older sea floor that is approximately correct for ages as young as 20 million years: Thus older seafloor deepens more slowly than younger and in fact can be assumed almost constant at ~6400 m depth. Parsons and Sclater concluded that some style of mantle convection must apply heat to

2006-618: The Pacific Ocean. The Pacific is also home to one of the world's most active spreading centers (the East Pacific Rise) with spreading rates of up to 145 ± 4 mm/yr between the Pacific and Nazca plates . The Mid-Atlantic Ridge is a slow-spreading center, while the East Pacific Rise is an example of fast spreading. Spreading centers at slow and intermediate rates exhibit a rift valley while at fast rates an axial high

2065-402: The asthenosphere from mantle plumes near the spreading center. Seafloor spreading occurs at spreading centers, distributed along the crests of mid-ocean ridges. Spreading centers end in transform faults or in overlapping spreading center offsets. A spreading center includes a seismically active plate boundary zone a few kilometers to tens of kilometers wide, a crustal accretion zone within

2124-457: The base of the continental crust which causes it to become more plastic and less dense. Because less dense objects rise in relation to denser objects, the area being heated becomes a broad dome (see isostasy ). As the crust bows upward, fractures occur that gradually grow into rifts. The typical rift system consists of three rift arms at approximately 120-degree angles. These areas are named triple junctions and can be found in several places across

2183-514: The boundary zone where the ocean crust is youngest, and an instantaneous plate boundary – a line within the crustal accretion zone demarcating the two separating plates. Within the crustal accretion zone is a 1–2 km-wide neovolcanic zone where active volcanism occurs. In the general case, seafloor spreading starts as a rift in a continental land mass , similar to the Red Sea - East Africa Rift System today. The process starts by heating at

2242-533: The change in water column height above the lithosphere as it expands or retracts. Both coefficients are related by: where ρ ∼ 3.3   g ⋅ c m − 3 {\displaystyle \rho \sim 3.3\ \mathrm {g} \cdot \mathrm {cm} ^{-3}} is the rock density and ρ 0 = 1   g ⋅ c m − 3 {\displaystyle \rho _{0}=1\ \mathrm {g} \cdot \mathrm {cm} ^{-3}}

2301-472: The continent is completely severed, then a new ocean basin is created. The Red Sea has not yet completely split Arabia from Africa, but a similar feature can be found on the other side of Africa that has broken completely free. South America once fit into the area of the Niger Delta . The Niger River has formed in the failed rift arm of the triple junction . As new seafloor forms and spreads apart from

2360-399: The continental crust is attenuated as far as it will stretch. At this point basaltic oceanic crust and upper mantle lithosphere begins to form between the separating continental fragments. When one of the rifts opens into the existing ocean, the rift system is flooded with seawater and becomes a new sea. The Red Sea is an example of a new arm of the sea. The East African rift was thought to be

2419-399: The elevation of the rift valley has been lowered to the point that the sea becomes stable. During this period of evaporation large evaporite deposits will be made in the rift valley. Later these deposits have the potential to become hydrocarbon seals and are of particular interest to petroleum geologists . Seafloor spreading can stop during the process, but if it continues to the point that

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2478-427: The fractures and cools on the ocean floor to form new seabed . Hydrothermal vents are common at spreading centers. Older rocks will be found farther away from the spreading zone while younger rocks will be found nearer to the spreading zone. Spreading rate is the rate at which an ocean basin widens due to seafloor spreading. (The rate at which new oceanic lithosphere is added to each tectonic plate on either side of

2537-414: The mantle half-space model, the seabed height is determined by the oceanic lithosphere and mantle temperature, due to thermal expansion. The simple result is that the ridge height or ocean depth is proportional to the square root of its age. Oceanic lithosphere is continuously formed at a constant rate at the mid-ocean ridges . The source of the lithosphere has a half-plane shape ( x = 0, z < 0) and

2596-406: The mid-ocean ridge it slowly cools over time. Older seafloor is, therefore, colder than new seafloor, and older oceanic basins deeper than new oceanic basins due to isostasy. If the diameter of the earth remains relatively constant despite the production of new crust, a mechanism must exist by which crust is also destroyed. The destruction of oceanic crust occurs at subduction zones where oceanic crust

2655-425: The mid-ocean ridge were the mirror image of those on the other side. By identifying a reversal with a known age and measuring the distance of that reversal from the spreading center, the spreading half-rate could be computed. In some locations spreading rates have been found to be asymmetric; the half rates differ on each side of the ridge crest by about five percent. This is thought due to temperature gradients in

2714-405: The motion of the continents is linked to seafloor spreading by the theory of plate tectonics, which is driven by convection that includes the crust itself as well. The driver for seafloor spreading in plates with active margins is the weight of the cool, dense, subducting slabs that pull them along, or slab pull. The magmatism at the ridge is considered to be passive upwelling, which is caused by

2773-575: The north end of a magnet, like a compass needle, points toward Earth's South magnetic field. Hydrology is the study of the hydrosphere and the movement of water on Earth . It emphasizes the study of how humans use and interact with freshwater supplies. Study of water's movement is closely related to geomorphology and other branches of Earth science. Applied hydrology involves engineering to maintain aquatic environments and distribute water supplies. Subdisciplines of hydrology include oceanography , hydrogeology , ecohydrology , and glaciology . Oceanography

2832-454: The ocean surface): The depth predicted by the square root of seafloor age derived above is too deep for seafloor older than 80 million years. Depth is better explained by a cooling lithosphere plate model rather than the cooling mantle half-space. The plate has a constant temperature at its base and spreading edge. Analysis of depth versus age and depth versus square root of age data allowed Parsons and Sclater to estimate model parameters (for

2891-419: The origin of landscapes. Structural geology studies the deformation of rocks to produce mountains and lowlands. Resource geology studies how energy resources can be obtained from minerals. Environmental geology studies how pollution and contaminants affect soil and rock. Mineralogy is the study of minerals and includes the study of mineral formation, crystal structure , hazards associated with minerals, and

2950-425: The physical and chemical properties of minerals. Petrology is the study of rocks, including the formation and composition of rocks. Petrography is a branch of petrology that studies the typology and classification of rocks. Plate tectonics , mountain ranges , volcanoes , and earthquakes are geological phenomena that can be explained in terms of physical and chemical processes in the Earth's crust. Beneath

3009-466: The planet has evolved and changed throughout long history. In Earth science, it is common to conceptualize the Earth's surface as consisting of several distinct layers, often referred to as spheres: the lithosphere , the hydrosphere , the atmosphere , and the biosphere , this concept of spheres is a useful tool for understanding the Earth's surface and its various processes these correspond to rocks , water , air and life . Also included by some are

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3068-418: The plates are sliding apart over the mantle upwelling in the process of ridge push. The depth of the seafloor (or the height of a location on a mid-ocean ridge above a base-level) is closely correlated with its age (age of the lithosphere where depth is measured). The age-depth relation can be modeled by the cooling of a lithosphere plate or mantle half-space in areas without significant subduction . In

3127-558: The plates being pulled apart under the weight of their own slabs. This can be thought of as analogous to a rug on a table with little friction: when part of the rug is off of the table, its weight pulls the rest of the rug down with it. However, the Mid-Atlantic ridge itself is not bordered by plates that are being pulled into subduction zones, except the minor subduction in the Lesser Antilles and Scotia Arc . In this case

3186-452: The problem; therefore the last term in the equation is neglected, giving a 1-dimensional diffusion equation: with the initial conditions The solution for z ≤ 0 {\displaystyle z\leq 0} is given by the error function : Due to the large velocity, the temperature dependence on the horizontal direction is negligible, and the height at time t (i.e. of sea floor of age t ) can be calculated by integrating

3245-423: The process by which the Earth is resurfaced. As the result of seafloor spreading , new crust and lithosphere is created by the flow of magma from the mantle to the near surface, through fissures, where it cools and solidifies. Through subduction , oceanic crust and lithosphere vehemently returns to the convecting mantle. Volcanoes result primarily from the melting of subducted crust material. Crust material that

3304-436: The thermal expansion over z : where α e f f {\displaystyle \alpha _{\mathrm {eff} }} is the effective volumetric thermal expansion coefficient, and h 0 is the mid-ocean ridge height (compared to some reference). The assumption that v is relatively large is equivalent to the assumption that the thermal diffusivity κ {\displaystyle \kappa }

3363-435: The world today. The separated margins of the continents evolve to form passive margins . Hess' theory was that new seafloor is formed when magma is forced upward toward the surface at a mid-ocean ridge. If spreading continues past the incipient stage described above, two of the rift arms will open while the third arm stops opening and becomes a 'failed rift' or aulacogen . As the two active rifts continue to open, eventually

3422-566: Was over 200 mm/yr during the Miocene on the East Pacific Rise . In the 1960s, the past record of geomagnetic reversals of Earth's magnetic field was noticed by observing magnetic stripe "anomalies" on the ocean floor. This results in broadly evident "stripes" from which the past magnetic field polarity can be inferred from data gathered with a magnetometer towed on the sea surface or from an aircraft. The stripes on one side of

3481-593: Was so high that a Western Interior Seaway formed across North America from the Gulf of Mexico to the Arctic Ocean . At the Mid-Atlantic Ridge (and in other mid-ocean ridges), material from the upper mantle rises through the faults between oceanic plates to form new crust as the plates move away from each other, a phenomenon first observed as continental drift. When Alfred Wegener first presented

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