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. Finally, the core is mostly iron metal. The mantle is hot and represents about 68 percent of Earth’s mass. 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. We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. It is the second concentric shell of the Earth that lies beneath the crust everywhere. The major structural components in the earth that are separated by sharp discontinuities are the crust, the mantle, and the core. It is the innermost concentric shell of the Earth as concluded from the record of seismic waves. At over 1000 degrees C, the mantle is solid but can deform slowly in a plastic manner. Being relatively cold, the crust is rocky and brittle, so it can fracture in earthquakes. Meteorites are considered to be the wandering fragments of planetary matter. This value reaches a figure of 12.7 g/cc at the boundary of the inner core and becomes 13.0 g/cc at the center of the earth. It is the center of the Earth, about 1,250 kilometers thick, and is the second smallest layer. It is made predominantly of basic minerals (rich in magnesium silicates) and hence is sometimes named as SIMA (Si for silica and Ma for magnesium). Similarly, the S-waves traveling at 3.35km/sec attain velocity of 4.35 km/sec. 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. Comparison of the earth with a large old apple will help in clarifying the concept of crust. The inner core, with a thickness of around 1,790 km is believed to be a solid metallic body. It occurs in the seismic records at depths of 30-40 km below the continents, 5-6 km below the oceans and 60-70 km below the mountains. The interior of the Earth has always been a mystery, something inaccessible because it is not possible to drill to its center. STRUCTURE AND COMPOSITION Each of these models is based on the idea of a concentric structure, composed of three main layers. 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. If you continue browsing the site, you agree to the use of cookies on this website. The study of seismic waves (released during earthquakes and nuclear shocks) forms the single most important source of information for the interior of the Earth. Thanks to this, at the moment, you have a very good idea about its composition and structure. Content Filtration 6. These forces occur because our planet is made up of numerous different geological processes. Other non-seismological grounds suggesting to a nickel iron core of the Earth are: (i) The High Density of the Earth as a Planet: It is fairly established that the mean density of the Earth is 5.517 g/cc. In the outer layer of the upper mantle. According to the studies, the lithosphere is not a continuous cover, but is divided into plates that move slowly on the surface of the Earth, to a few centimeters per year. Because of this, the electric currents that originate the Earth's magnetic field are produced. (Fig. As the surface of the Earth cooled, the rocky materials solidified and so the primitive crust formed. The continental crust is much older than the oceanic crust. This layer (the crust) is merely 35 km thick (on an average) below the continental surfaces and about 5-6 km thick under the oceans. The P and S waves travel through the body of the earth and hence are distinguished as body waves. See our Privacy Policy and User Agreement for details. The core is composed mostly of iron (Fe) and is so hot that the outer core is molten, with about 10% sulphur (S). The exact nature of the mantle is as yet incompletely understood. (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 crust, mainly in the continental zones, is the most heterogeneous part of the Earth, and it undergoes continuous changes due to the action of opposing forces, the endogenous or constructive ones of relief, and the exogenous that … The crust is to the earth what skin is to an old apple – a very thin, hard and wrinkled sheet of rock covering. The nucleus is divided into two zones: outer nucleus and inner nucleus. See our User Agreement and Privacy Policy. 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. You can change your ad preferences anytime. This is due to a change from a plastic mantle or layer to a rigid one.
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