The mantle is hot and represents about 68 percent of Earth’s mass. It is the innermost concentric shell of the Earth as concluded from the record of seismic waves. It is the most superficial layer of the Earth and the thinnest, constituting only 1% of its mass, is in contact with the atmosphere and the hydrosphere. It is the most superficial layer of the Earth and the thinnest, constituting only 1% of its mass, is in contact with the atmosphere and the hydrosphere. Image Guidelines 4. The Continental Crust is further distinguished into three layers- A, B and C. The A or the Upper Layer is between 2-10 km thick and is of low density (2.2 g/cc). Function of the layers The lithosphere is made up of rigid lithospheric plates floating over the underlying plastic asthenosphere. The density for the materials of mantle is also calculated to range from 3.3 to 5.7 g/cc. Enough seismic data is available to suggest that density in the mantle rises from 3.3 g/cc from just below the crust to about 5.7g/cc at the base of the mantle. The final picture of the internal structure of the Earth as developed from the study of the seismic wave records of the earthquakes divides it into three well defined shells or zones or spheres- the Crust, the Mantle and the Core. It has been sub-divided into an upper and lower mantle, the boundary between the two layers being placed at 900-1,000 km below the earth. The inner core is under such extreme pressure that it remains solid. The asthenosphere is also in motion. Comparison of the earth with a large old apple will help in clarifying the concept of crust. The seismic waves travel in all directions from the focus. (ii) The three types of seismic waves are recorded during each earthquake in a definite sequence at various seismographic stations; their records are known as seismograms. The internal structure of the Earth is made up of the asthenosphere, the upper mantle, the lower mantle, the outer core and the inner core. Prohibited Content 3. It is the deepest part of the Earth, has a radius of 3,500 kilometers and represents 60% of its total mass. STRUCTURE AND COMPOSITION The real interior of the Earth is nowhere exposed to our direct observation. The most important facts about seismic waves as are relevant to the internal structure of the earth are summarized as follows: (i) In every earthquake elastic waves of three main types are generated at the focus (point of origin below the surface) of the earthquake. Shock waves developed during big explosions are similar in all details to seismic waves. The oceanic crust constitutes the bottoms of the oceans. Its main function is that of thermal insulation. It is named after its discoverer, Beno Gutenberg, a German seismologist who discovered it in 1.914. It has an average thickness of 7 kilometers and is formed by dense rocks, essentially basalt and gabbro. See our User Agreement and Privacy Policy. This explains the slow movement of tectonic plates. It is below the crust and is the largest layer, occupying 84% of the volume of the Earth and 65% of its mass. At over 1000 degrees C, the mantle is solid but can deform slowly in a plastic manner. Seismology is a branch of geophysics that deals with the study of elastic or seismic waves generated within the earth during an earthquake. The earth is divided into four main layers: the inner core, outer core, mantle, and crust. Such a gradual and uniform increase with increasing depth is on expected lines since their velocity is related to density of the medium which is normally expected to increase with depth. It is approximately 1,221 km thick and has a density of 12.8g/cm3 at the top of the section and 13.1g/cm3 at its deepest point. It is an area where the iron is in the liquid state. It is argued by many that the iron meteorites are actually fragments from the core of a planet or planet like body of our solar system that has suffered disintegration during the process of evolution of solar system. Further, the depths calculated from these discontinuities show remarkable agreement and hence may be taken as demarcating zones of different material composition within the earth. This zone starting from the lower boundary of the crust continues up to a depth of 2,900 km. Since the beginning of studies about the interior of the Earth, many models have been proposed to describe its internal structure (Educational, 2017). The second discontinuity, recorded at depth of 2,900 km, while demarcating the end of Mantle also marks the beginning of the third major zone of the Earth that is named as CORE. STRUCTURE c. Ataxites- Fine grained in nature and contains nickel in still higher proportions. Clipping is a handy way to collect important slides you want to go back to later. The layers that make up the inner part of the earth are: the outer shell or shell, the mantle or middle layer, and the inner shell or core. Because of this, the electric currents that originate the Earth's magnetic field are produced. D. VELOSITY AND DENSITY VARIATION Copyright 9. (i) From the study of travel time curves of these waves as obtained from various earthquake records, it is possible to calculate the velocity of any one type of these waves at any depth within the earth. DETERMINING THE EARTH'S INTERNAL It is observed that both P and S waves on reaching these depths undergo sharp increase in their velocity. We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. The mantle is composed of magnesium, iron silicates, sulfides and silicon oxides. It is part of the lithosphere and its name comes from the Greek lithos, which means stone. In every major earthquake, P and S waves are recorded at all the stations lying between the epicenter and 142° arc distance (11,000 km); further between 105° and 142° arc distances (11,000-16,000 km), only P waves reappear. The inner core is solid and is composed of iron and nickel. Not all ocean waters are part of this crust, there is a surface area corresponding to the continental crust. C. THE EARTH'S INTERNAL LAYERED A. The nucleus is divided into two zones: outer nucleus and inner nucleus. Critically Evaluate the cyclone preparedness Program (CPP) of Bangladesh. If we cut a piece of fruit in half, we will see that it is composed of three parts: 1) a very thin skin, 2) a seed of significant size located in the center, and 3) most of the mass of the fruit being contained within the flesh. Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. Conversely, a major change in the velocity of seismic waves at some specific depths below the surface in numerous records can be taken to mean there is a change in the nature of medium (material) at that particular depth. 2.6). The behavior of P and S waves below the depth of 2,900 km throws sufficient light on the existence of the third major shell, the Core. As of this date, Scribd will manage your SlideShare account and any content you may have on SlideShare, and Scribd's General Terms of Use and Privacy Policy will apply. The P-waves attain a velocity of 7.75 km/sec from an original velocity of 5.4 km/sec in the immediately overlying layer. It is of fundamental importance in the interpretation of the internal structure of the Earth. The thickness of the crust is varied; the thickest part is on the continents, under the great mountain ranges, where it can reach 60 kilometers. It is believed to be the source of much volcanic activity of the Earth and many other processes. This material is a good conductor of electricity and circulates at high speed on the outside. It comprises the earth's crust and the upper and colder part of the mantle, distinguished as a lithosphere mantle. It is generally the extension of C layer of the continental crust that makes the top layer of the oceans in most cases; A and B layers being practically absent from there. At the bottom of the ocean it barely exceeds 10 kilometers. This zone has been named as asthenosphere (Greek “asthenes” – without strength). It is approximately 2,259 km thick. Although it is one of the smaller layers, the inner core is the warmest layer. Core, mantle, and crust are divisions based on composition. In the crust is a rocky bed, made mainly of solid silicate rocks such as granite and basalt. The asthenosphere is a semisolid layer of hot rock that's found at the top of the upper mantle. It was first discovered from the seismic records by B.Gutenberg in 1918 and subsequently confirmed by Jefferys in 1939. Very significant variations in the density of material immediately outside and inside of the core are suggested by seismic observations. The continental crust forms the continents, its average thickness is 35 kilometers, but can reach more than 70 kilometers. 1. The crust is to the earth what skin is to an old apple – a very thin, hard and wrinkled sheet of rock covering.

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