{"id":2502,"date":"2026-03-04T12:18:39","date_gmt":"2026-03-04T06:48:39","guid":{"rendered":"https:\/\/vajiramandravi.com\/upsc-exam\/?p=2502"},"modified":"2026-03-10T12:26:36","modified_gmt":"2026-03-10T06:56:36","slug":"interior-of-the-earth","status":"publish","type":"post","link":"https:\/\/vajiramandravi.com\/upsc-exam\/interior-of-the-earth\/","title":{"rendered":"Interior of the Earth Sources and Structure"},"content":{"rendered":"<p>The interior of the Earth can be divided into several layers based on the chemical composition and mechanical stability. Based on these characteristics, Earth\u2019s internal structures are divided into crust, lithosphere, asthenosphere, mantle, outer core and inner core. Except for the liquid outer core, all the other layers are solid, including the semi-molten asthenosphere. The difference in the chemical and physical nature of the Earth\u2019s layers is due to differential temperature, pressure and density which have been shaped during the evolution of these layers.<\/p>\r\n<p>The internal structures of Earth have been proposed based on direct and indirect sources such as seismic waves which behave differently in the Earth\u2019s layers depending on the composition and physical nature of these layers.<\/p>\r\n<h2>Sources for the Interior of the Earth<\/h2>\r\n<p>The materials of the earth\u2019s surface are different from the interior. Therefore, to study the Earth\u2019s internal structure, direct and indirect sources are taken into consideration.<\/p>\r\n<ul>\r\n\t<li><strong>Direct Sources:\u00a0<\/strong>\r\n<ul>\r\n\t<li><strong>Mining:\u00a0<\/strong>The most readily available earth material is its minerals, which can be obtained through mining. Mines can be very deep also, for example, Gold mines in\u00a0<strong>South Africa<\/strong>\u00a0are as deep as 3 - 4 km.<\/li>\r\n\t<li><strong>Drilling Projects<\/strong>: There are many projects to penetrate deeper depths to explore the conditions in the crustal portions such as the \u201c<strong>Deep Ocean Drilling Project\u201d and \u201cIntegrated Ocean Drilling Project\u201d.<\/strong><\/li>\r\n\t<li><strong>Volcanic eruption:<\/strong>\u00a0During a volcanic eruption, molten material (<strong>magma<\/strong>) explodes onto the earth's surface and is then available for laboratory investigation. However, it is difficult to determine the depth of the magma's source.<\/li>\r\n<\/ul>\r\n<\/li>\r\n\t<li><strong>Indirect Sources:<\/strong>\r\n<ul>\r\n\t<li><strong>Temperature, Pressure, and Density:<\/strong>\u00a0Knowing the total thickness of the earth, scientists have estimated the values of temperature, pressure, and the density of materials at different depths.<\/li>\r\n\t<li><strong>Seismic Activity: The shadow zones of P- and S- waves help understand the different densities of the Earth\u2019s layers.<\/strong><\/li>\r\n\t<li>For example, the S-waves cannot be transmitted through fluids. The sudden \u201cshadow\u201d where s-waves disappear indicates that the Earth had a\u00a0<strong>liquid outer core<\/strong>.<\/li>\r\n\t<li>Different\u00a0<strong>discontinuities\u00a0<\/strong>within the Earth\u2019s interiors are based on the propagation and velocities of seismic waves through the layers of the Earth.<\/li>\r\n\t<li><strong>Gravitation:<\/strong>\u00a0The gravitational force differs at different latitudes on the Earth. Gravity anomalies provide information on the mass distribution of materials in the Earth.<\/li>\r\n\t<li><strong>Magnetic surveys:\u00a0<\/strong>These also offer information regarding the distribution of\u00a0<strong>magnetic materials<\/strong>\u00a0in the crustal portion, as well as the distribution of materials in this region.<\/li>\r\n<\/ul>\r\n<\/li>\r\n\t<li><strong>Meteors: The material and the structure observed in the meteors are similar to that of the Earth. Hence, this becomes a source of information about the interior of the Earth.<\/strong><\/li>\r\n<\/ul>\r\n<h2>Structure of the Earth<\/h2>\r\n<p>Earth is made up of\u00a0<strong>several layers.\u00a0<\/strong>According to the mechanical properties, Earth's layers are the\u00a0<strong>Lithosphere<\/strong>,\u00a0<strong>Asthenosphere<\/strong>,\u00a0<strong>Lower mantle<\/strong>\u00a0(also known as mesospheric mantle), Outer core, and Inner core. Chemically, the layers are the Crust, Mantle, and Core.<\/p>\r\n<h3>Evolution of the Earth\u2019s Layered Structure<\/h3>\r\n<p>When Earth was formed about 4.5 billion years ago, it was a uniform ball of hot rock.\u00a0<strong>Radioactive decay\u00a0<\/strong>and\u00a0<strong>leftover heat<\/strong>\u00a0from planetary formation caused the ball to get even hotter.<\/p>\r\n<ul>\r\n\t<li><strong>Iron Catastrophe:\u00a0<\/strong>Eventually, after about 500 million years, Earth\u2019s temperature heated to the melting point of iron\u2014about 1,538\u00b0 Celsius. This key stage in Earth's history is known as the\u00a0<strong>Iron Catastrophe.\u00a0<\/strong>The iron catastrophe allowed more rapid movement of Earth\u2019s molten, rocky material.<\/li>\r\n\t<li><strong>Formation of layers:<\/strong>The early core was formed when droplets of iron, nickel, and other heavy metals gravitated to the\u00a0<strong>Earth's center\u00a0<\/strong>to form the core of the new planet.\u00a0<strong>Relatively buoyant materials<\/strong>, such as silicates, and water, stayed close to the planet\u2019s exterior.\r\n\r\n<ul>\r\n\t<li>This process is known as\u00a0<strong>planetary differentiation.\u00a0<\/strong><\/li>\r\n\t<li>The molten material that surrounded the core was the early mantle.<\/li>\r\n\t<li>Materials that initially stayed in their liquid phase during this process, called\u00a0<strong>\u201cincompatible elements,\u201d<\/strong>\u00a0ultimately became\u00a0<strong>Earth\u2019s brittle crust<\/strong>. The crusts are still evolving due to\u00a0<a href=\"https:\/\/vajiramandravi.com\/current-affairs\/plate-tectonics-theory\/\" target=\"_blank\"><strong>plate tectonics<\/strong><\/a>.<\/li>\r\n<\/ul>\r\n<\/li>\r\n\t<li><strong>Solidification of Mantle:<\/strong>\u00a0Water held within minerals erupted as lava, a process known as\u00a0<strong>\"outgassing.\"<\/strong>\u00a0As more water was expelled, the mantle solidified.<\/li>\r\n<\/ul>\r\n<h3>Thermal and Physical State of Earth\u2019s Interior<\/h3>\r\n<p><strong>Temperature<\/strong>,\u00a0<strong>pressure,\u00a0<\/strong>and\u00a0<strong>density\u00a0<\/strong>are responsible for the generation of the present state of affairs.<\/p>\r\n<ul>\r\n\t<li><strong>Temperature:\u00a0<\/strong>In deep wells and mines, the temperature rises as the depth increases.This evidence along with\u00a0<strong>molten lava<\/strong>\u00a0erupting from the<strong>\u00a0earth\u2019s interior<\/strong>, supports that temperature increases towards the center of the earth.\r\n\r\n<ul>\r\n\t<li>The pace of increase is not linear. Within the upper 100 kilometers, the\u00a0<strong>temperature gradient\u00a0<\/strong>is between 15\u00b0 and 30\u00b0C per kilometer. It then decreases substantially through the mantle, increases more swiftly at the base of the mantle, and finally gradually increases through the core.<\/li>\r\n\t<li>The temperature is around\u00a0<strong>1000\u00b0C\u00a0<\/strong>at the\u00a0<strong>crust's\u00a0<\/strong>base,\u00a0<strong>3500\u00b0C\u00a0<\/strong>at the\u00a0<strong>mantle's\u00a0<\/strong>base, and\u00a0<strong>5,000\u00b0C<\/strong>\u00a0at the\u00a0<strong>Earth's center.<\/strong><\/li>\r\n\t<li>The disintegration of\u00a0<strong>radioactive elements<\/strong>\u00a0and chemical reactions occurring under high pressure may be the reason for the earth's extremely high temperature.<\/li>\r\n<\/ul>\r\n<\/li>\r\n\t<li><strong>Pressure:<\/strong>\u00a0Due to the enormous weight of the overlying rocks, there is also an increase in pressure from the surface of the earth towards its core. As a result, the pressure is extremely high in deeper areas.\r\n\r\n<ul>\r\n\t<li>The pressure near the center is considered to be 3 to 4 million times thepressure of the atmosphere at sea level.<\/li>\r\n<\/ul>\r\n<\/li>\r\n\t<li><strong>Density:<\/strong>On average, the density of the Earth\u2019s interior is\u00a0<strong>5.5 g\/cm3.\u00a0<\/strong>Due to the increase in pressure and presence of heavier materials towards the earth\u2019s center, the density of the earth\u2019s layers also increases.<\/li>\r\n<\/ul>\r\n<h2>Crust<\/h2>\r\n<p>The crust is the uppermost layer of the Earth. It possesses just\u00a0<strong>1% of Earth\u2019s mass<\/strong>\u00a0but contains almost all known life in the universe. The crust, created by the dynamic geologic forces, continues to be shaped by the planet\u2019s movement and energy.\u00a0<strong>Plate tectonics<\/strong>\u00a0is responsible for the formation and\u00a0<strong>destruction of crustal materials.<\/strong><\/p>\r\n<ul>\r\n\t<li><strong>Composition:<\/strong>\u00a0It is made up of\u00a0<strong>solid rocks\u00a0<\/strong>and\u00a0<strong>minerals<\/strong>.\r\n\r\n<ul>\r\n\t<li>Earth\u2019s crust is composed of<strong>\u00a0igneous, metamorphic, and sedimentary rocks.\u00a0<\/strong><\/li>\r\n\t<li><strong>Igneous rocks<\/strong>\u00a0such as\u00a0<strong>granite\u00a0<\/strong>and\u00a0<strong>basalt,\u00a0<\/strong>which form when magma cools, are the most prevalent types of rocks in the crust.<\/li>\r\n<\/ul>\r\n<\/li>\r\n\t<li><strong>Density:\u00a0<\/strong>less than 2.7 g\/cm3.<\/li>\r\n\t<li><strong>Types:\u00a0<\/strong>The crust is\u00a0<strong>subdivided into two types<\/strong>\u00a0-\u00a0<strong>oceanic\u00a0<\/strong>and\u00a0<strong>continental<\/strong>\u00a0crusts.\r\n\r\n<ul>\r\n\t<li><strong>The oceanic crust<\/strong>\u00a0is found under\u00a0<strong>oceans<\/strong>.<\/li>\r\n\t<li>The continental crust floats higher on the mantle because it is less dense than the oceanic crust.<\/li>\r\n<\/ul>\r\n<\/li>\r\n\t<li><strong>Discontinuity:\u00a0<\/strong>The transition zone between oceanic and continental crust is known as\u00a0<strong>Conrad discontinuity.<\/strong><\/li>\r\n<\/ul>\r\n<figure>\r\n<table>\r\n<tbody>\r\n<tr>\r\n<td class=\"tb-color\" colspan=\"3\"><strong>Difference between Oceanic and Continental Crust<\/strong><\/td>\r\n<\/tr>\r\n<tr>\r\n<td><strong>Features<\/strong><\/td>\r\n<td><strong>Oceanic Crust<\/strong><\/td>\r\n<td><strong>Continental Crust<\/strong><\/td>\r\n<\/tr>\r\n<tr>\r\n<td><strong>Composition<\/strong><\/td>\r\n<td>\r\n<p>- Mafic and ultramafic intrusive igneous.<\/p>\r\n<p>- Rocks of the oceanic crust referred to as \u201c<strong>SiMa\u201d,\u00a0<\/strong>stand for\u00a0<strong>Silicate and Magnesium<\/strong>, the most abundant minerals in the oceanic crust.<\/p>\r\n<\/td>\r\n<td>\r\n<p>- Granitic (felsic) intrusive igneous rocks.<\/p>\r\n<p>- The term\u00a0<strong>\"SiAl\"<\/strong>\u00a0refers to rocks of the continental crust that contain silicate and aluminium, the most abundant minerals in the crust.<\/p>\r\n<\/td>\r\n<\/tr>\r\n<tr>\r\n<td><strong>Formation<\/strong><\/td>\r\n<td>- Formed from magma that rose from the mantle and cooled at the ocean floor.<\/td>\r\n<td>- Formed from the melting of rocks and the accumulation of sediments.<\/td>\r\n<\/tr>\r\n<tr>\r\n<td><strong>Mineralogy<\/strong><\/td>\r\n<td>- Rich in iron and magnesium<\/td>\r\n<td>- Rich in silicon and oxygen<\/td>\r\n<\/tr>\r\n<tr>\r\n<td><strong>Thickness<\/strong><\/td>\r\n<td>- Oceanic crust is typically about 5-10 kilometers thick.<\/td>\r\n<td>- Continental crust can be up to 40 kilometers thick.<\/td>\r\n<\/tr>\r\n<tr>\r\n<td><strong>Density<\/strong><\/td>\r\n<td>- 2.9 grams per cubic centimeter<\/td>\r\n<td>- 2.7 grams per cubic centimeter<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<\/figure>\r\n<h2>Mantle<\/h2>\r\n<p>It is the 2,900 km thick layer between Earth\u2019s dense, superheated core and its thin outer layer, the crust.<\/p>\r\n<ul>\r\n\t<li><strong>Volume:<\/strong>\u00a0The mantle lies below the crust and is by far the largest layer making up\u00a0<strong>84%\u00a0<\/strong>of Earth's volume and\u00a0<strong>67<\/strong>% of the Earth\u2019s mass.<\/li>\r\n\t<li><strong>Density:\u00a0<\/strong>The density of the mantle is3.9 g\/cm3.<\/li>\r\n\t<li><strong>Composition:<\/strong>\u00a0The majority of the rocks that make up the mantle of the Earth are\u00a0<strong>silicates<\/strong>.\r\n\r\n<ul>\r\n\t<li>Olivine, garnet, and pyroxene are the common silicates found in Mantle.<\/li>\r\n\t<li>Magnesium oxide is the other main type of rock that can be found in the mantle.<\/li>\r\n\t<li>Other elements include aluminium, iron, calcium, sodium, and potassium.<\/li>\r\n<\/ul>\r\n<\/li>\r\n\t<li><strong>Discontinuity:<\/strong>\u00a0The Mohorovicic Discontinuity, or Moho, marks the beginning of the mantle. The Moho is defined as the\u00a0<strong>density\u00a0<\/strong>contrast from less<strong>\u00a0dense crust<\/strong>\u00a0to the<strong>\u00a0denser mantle<\/strong>\u00a0and whereseismic wave velocities increase.<\/li>\r\n<\/ul>\r\n<h3>Layers of Mantle<\/h3>\r\n<p>The Earth\u2019s Mantle is divided into mainly two layersi.e.,<strong>\u00a0the Upper mantle and the Lower mantle.\u00a0<\/strong>The discontinuity between the\u00a0<strong>upper mantle<\/strong>\u00a0and the<strong>\u00a0lower mantle<\/strong>\u00a0is known as\u00a0<strong>Repetti Discontinuity.\u00a0<\/strong><\/p>\r\n<ul>\r\n\t<li><strong>Upper Mantle:<\/strong>\u00a0Despite being mostly solid, the upper mantle's more malleable regions contribute to\u00a0<strong>tectonic<\/strong>\u00a0activity.\r\n\r\n<ul>\r\n\t<li>The thickness of the Upper mantle is around 410 Kms.<\/li>\r\n\t<li>Two parts of the upper mantle are often recognized as distinct regions in\u00a0<strong>Earth\u2019s interior<\/strong>\u00a0i.e., the\u00a0<strong>lithosphere\u00a0<\/strong>and the\u00a0<strong>asthenosphere<\/strong>.<\/li>\r\n<\/ul>\r\n<\/li>\r\n\t<li><strong>Transition zone: It is present at the depth from 410 Km to 660 Km.<\/strong><\/li>\r\n\t<li>It prevents the large exchanges of material between the lower and upper mantle.<\/li>\r\n\t<li>The most important aspect of the mantle\u2019s transition zone is its abundance of water. Crystals in the transition zone hold as much water as all the oceans on Earth\u2019s surface.<\/li>\r\n\t<li><strong>Lower Mantle:<\/strong>\u00a0The lower mantle extends from about 660 kilometers to about 2,700 kilometers beneath Earth\u2019s surface.\r\n\r\n<ul>\r\n\t<li>Compared to the upper mantle, the lower mantle is hotter and denser.<\/li>\r\n<\/ul>\r\n<\/li>\r\n\t<li><strong>D\u2019\u2019 (D-double prime):<\/strong>\u00a0It is a shallow region beneath the lower mantle.\r\n\r\n<ul>\r\n\t<li>In some areas, it is a<strong>\u00a0razor-thin boundary<\/strong>\u00a0with the outer core while in others, it has thick accumulations of iron and silicates.<\/li>\r\n<\/ul>\r\n<\/li>\r\n<\/ul>\r\n<h3>Lithosphere<\/h3>\r\n<p>It is the\u00a0<strong>solid<\/strong>, outer part of\u00a0<strong>Earth.\u00a0<\/strong>It is made up of the crust and the upper mantle, above the asthenosphere. Of all the layers of the Earth, the lithosphere is both the\u00a0<strong>coolest\u00a0<\/strong>and the\u00a0<strong>most rigid<\/strong>.<\/p>\r\n<ul>\r\n\t<li><strong>Thickness:<\/strong>\u00a0The average thickness of the lithosphere<strong>\u00a0is 100 km<\/strong>\u00a0and may\u00a0<strong>go up to 300 km<\/strong>\u00a0below the\u00a0<strong>orogenic mountains<\/strong>.\r\n\r\n<ul>\r\n\t<li>The thickness of the lithosphere is less than 50 km below the\u00a0<strong>oceanic crust.<\/strong><\/li>\r\n<\/ul>\r\n<\/li>\r\n\t<li><strong>Composition:<\/strong>\u00a0The lithosphere consists of many different large segments or blocks, called\u00a0<strong>lithospheric plates or tectonic plates.<\/strong>\r\n<ul>\r\n\t<li>These plates are considered rigid bodies floating horizontally over the\u00a0<strong>asthenosphere<\/strong>, and\u00a0<strong>tectonic deformations<\/strong>\u00a0typically occur at the plate boundaries as a result of plate interactions with other plates.<\/li>\r\n<\/ul>\r\n<\/li>\r\n<\/ul>\r\n<h3>Asthenosphere<\/h3>\r\n<p>The asthenosphere is a\u00a0<strong>hot<\/strong>,\u00a0<strong>soft<\/strong>, mechanically weak, ductile and\u00a0<strong>semi-viscous<\/strong>\u00a0region and consists of semi-molten rock materials.<\/p>\r\n<ul>\r\n\t<li><strong>Properties:\u00a0<\/strong>The Asthenosphere is part of the\u00a0<strong>upper mantle<\/strong>\u00a0also known as<strong>\u00a0the Low-Velocity Zone (LVZ)<\/strong>\u00a0because the velocity of<strong>\u00a0seismic wavesdecreases\u00a0<\/strong>in this zone.\r\n\r\n<ul>\r\n\t<li>This zone allows the\u00a0<strong>lithospheric plate to float<\/strong>\u00a0and move over it.<\/li>\r\n<\/ul>\r\n<\/li>\r\n\t<li><strong>Thickness:\u00a0<\/strong>The average thicknessis between 180 to 220 km.<\/li>\r\n\t<li><strong>Depth:\u00a0<\/strong>It\u00a0<strong>lies below the lithosphere<\/strong>\u00a0at an average depth of 100 km and extends to a depth of 350 to 650 km.<\/li>\r\n\t<li><strong>Composition:<\/strong>\u00a0It is composed of peridotite rock, containing mostly the olivine and pyroxene minerals.<\/li>\r\n<\/ul>\r\n<h2>Core<\/h2>\r\n<p>The extremely hot and dense center of our planet is known as the Earth's core. The\u00a0<strong>Gutenberg discontinuity<\/strong>\u00a0signals the end of the mantle and the commencement of Earth's liquid outer core.<\/p>\r\n<ul>\r\n\t<li><strong>Volume:\u00a0<\/strong>The core accounts for 33% of the Earth\u2019s mass and 16 percent of the Earth\u2019s volume.<\/li>\r\n\t<li><strong>Composition:<\/strong>\u00a0Unlike the mineral-rich mantle and crust, it is made almost entirely of metal - iron (Fe) and nickel (Ni) hence, sometimes called\u00a0<strong>NiFe layer.<\/strong><\/li>\r\n\t<li><strong>Siderophiles, the elements that dissolve in iron (gold, platinum, cobalt, etc) are also found in the core.<\/strong><\/li>\r\n\t<li>The core contains\u00a0<strong>90% of the earth's sulfur.<\/strong><\/li>\r\n\t<li>The other elements speculated to be the parts of the core are\u00a0<strong>oxygen\u00a0<\/strong>and\u00a0<strong>silicon<\/strong>.<\/li>\r\n\t<li><strong>Two layers:\u00a0<\/strong>The core is further divided into two layers -\u00a0<strong>inner core<\/strong>\u00a0and\u00a0<strong>outer core.\u00a0<\/strong>The\u00a0<strong>Lehmann discontinuity<\/strong>\u00a0or the\u00a0<strong>Bullen discontinuity<\/strong>\u00a0is the boundary separating these regions.<\/li>\r\n<\/ul>\r\n<h3>Outer Core<\/h3>\r\n<p>The 2,200 km thick outer core is composed of liquid iron and nickel, in a<strong>\u00a0molten state<\/strong>.<\/p>\r\n<ul>\r\n\t<li><strong>Properties:<\/strong>\u00a0The hottest part of the core (at the Bullen discontinuity) is as hot as the surface of the sun (around 6,000\u00b0 Celsius).\r\n\r\n<ul>\r\n\t<li>The liquid metal in the outer core has<strong>\u00a0low viscosity.<\/strong><\/li>\r\n<\/ul>\r\n<\/li>\r\n\t<li><strong>Earth's magnetic field: The Earth's magnetic field is created in the outer core by a self-exciting dynamo process.\u00a0<\/strong><\/li>\r\n\t<li>The magnetic field is generated by electrical currents flowing through slow-moving molten iron.<\/li>\r\n<\/ul>\r\n<h3>Inner core<\/h3>\r\n<p>Earth\u2019s inner core is\u00a0<strong>solid\u00a0<\/strong>andextends from<strong>\u00a05150 Km to 6370 Km,<\/strong>\u00a0and is mostly composed of\u00a0<strong>iron.<\/strong><\/p>\r\n<ul>\r\n\t<li><strong>Solid core: Despite the temperature of the inner core being more than the melting point of iron, the inner core is solid.\u00a0<\/strong><\/li>\r\n\t<li>This is due to the intense pressure and density of the inner core.<\/li>\r\n\t<li><strong>Rotation:\u00a0<\/strong>The inner core rotates eastward but at a little faster rate than the other part of the Earth.<\/li>\r\n\t<li><strong>Growth:\u00a0<\/strong>The inner core grows by about a millimeter every year as the Earth is slowly cooling.<\/li>\r\n\t<li>Consequently, the outer core is solidifying or freezing.<\/li>\r\n<\/ul>\r\n<table style=\"border-collapse: collapse;width: 100%;height: 210px\">\r\n<tbody>\r\n<tr style=\"height: 25px\">\r\n<td class=\"tb-color\" style=\"width: 100%;text-align: center;height: 25px\" 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href=\"https:\/\/vajiramandravi.com\/upsc-exam\/godavari-river-system\/\" target=\"_blank\"><strong>Godavari River System<\/strong><\/a><\/td>\r\n<td style=\"width: 50%;text-align: center;height: 25px\"><a href=\"https:\/\/vajiramandravi.com\/upsc-exam\/tsunami\/\" target=\"_blank\"><strong>Tsunami<\/strong><\/a><\/td>\r\n<\/tr>\r\n<tr style=\"height: 25px\">\r\n<td style=\"width: 50%;text-align: center;height: 25px\"><strong><a href=\"https:\/\/vajiramandravi.com\/upsc-exam\/big-bang-theory\/\" target=\"_blank\">Big Bang Theory<\/a> <\/strong><\/td>\r\n<td style=\"width: 50%;text-align: center;height: 25px\"><a href=\"https:\/\/vajiramandravi.com\/upsc-exam\/western-disturbances-in-india\/\" target=\"_blank\"><strong>Western Disturbances in India<\/strong><\/a><\/td>\r\n<\/tr>\r\n<tr style=\"height: 25px\">\r\n<td style=\"width: 50%;text-align: center;height: 25px\"><a href=\"https:\/\/vajiramandravi.com\/upsc-exam\/latitudes-and-longitudes\/\" target=\"_blank\"><strong>Latitude and Longitude<\/strong><\/a><\/td>\r\n<td style=\"width: 50%;text-align: center;height: 25px\"><a href=\"https:\/\/vajiramandravi.com\/upsc-exam\/the-universe-origin-and-its-composition\/\" target=\"_blank\"><strong>The Universe<\/strong><\/a><\/td>\r\n<\/tr>\r\n<tr style=\"height: 25px\">\r\n<td style=\"width: 100%;text-align: center;height: 25px\" colspan=\"2\"><a href=\"https:\/\/vajiramandravi.com\/upsc-exam\/asteroid\/\" target=\"_blank\"><strong>Asteroid<\/strong><\/a><\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>","protected":false},"excerpt":{"rendered":"<p> Three major layers that make up the interior structure of the Earth are crust, mantle, and core each having a distinct chemical composition and physical 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