The Crust, Mantle And Core



The inside of the earth, idealised, can be described as a series of concentric shells made up of layers. Since the time of Isaac Newton, who noted in a discussion of the planets that the average density of the earth is five to six times that of water, it has been recognised that the earth is not a homogeneous, structureless body. 
The earth's average density is 5.5 g per em3 (grams per cubic centimetre), and because the average density of surface rocks is only 2.8 g per em3, there must be a large mass of higher-density material inside the earth.
• We can deduct from this and other evidence that the earth has a large central mass. Indeed, over the last 60 years, geophysicists and geologists have increased their confidence in estimating the thickness and characteristics of each of the earth's successive layers, including variations within some layers. 
• Man has looked into the earth in deep mines and drilled holes for only a small portion of the 4,000-mile distance to the earth's centre, about 5 miles. Furthermore, because man will almost certainly never be able to drill a hole into the deep interior, we must rely on indirect evidence to learn about it.
At the moment, this evidence consists of:
(1) Direct observations of rocks at the surface, 
(2) Secondary observations based on geophysical phenomena (such as waves through the earth caused by earthquakes and explosive sources, planetary motions of the earth, the flow of heat from the interior, the magnetic field, and gravitational attraction),
(3) Laboratory experiments on surface rocks and minerals, and 
(4) Laboratory experiments on surface rocks and minerals. 
All of these sources have contributed to our current understanding of the earth's structural features and composition. We will use facts from these sources to consider layering, the existence of openings, and the physical state and composition of the rocks and minerals presumed to occur in the earth in the following discussion of the interior of the earth. Our composition estimates are currently no better than conjectures, but they are reasonably consistent with geophysical observations.


•    Compressional waves, P, in which solid particles move back and forth parallel to the direction of travel, and shear waves, S, in which particle motion is across, transverse to the direction of travel, are the two types of earthquake waves transmitted through the earth. Geophysicists study earthquake wave velocity and paths to learn more about the earth's interior.
•    In 1909, one of them, a Yugoslav named Mohorovicic (pronounced Mo-ho-ro-vee-chich), discovered a discontinuity between the crust and the mantle by observing a sharp increase in the velocity of earthquake waves as they passed through the crust. 
•    The discontinuity is sometimes referred to as the M discontinuity, or more colloquially as the "Moho" and a hole proposed to be drilled through it is referred to as the "Mohole."


•    It is the earth's solid outermost layer. It has a brittle texture. The crust thickness varies between oceanic and continental areas. When compared to continental crust, the oceanic crust is thinner. The oceanic crust has a thickness of 5 kilometres, while the continental crust has a thickness of around 30 kilometres. 
•    In the areas of major mountain systems, the continental crust is thicker. In the Himalayan region, it can be up to 70 kilometres thick. It is composed of denser rocks with a density of 3 g/cm3. Basalt is a type of rock found in the oceanic crust. Material density in the oceanic crust is 2.7 g/cm3.
•    Granite and basalt are the two basic rock types that make up the crust. Granite makes up the majority of the continental crust. Basalt is a volcanic lava rock that makes up the oceanic crust. 
The continental crust is primarily composed of:
(1)    Dense light-coloured igneous rocks like granite or quartz diorite in the upper part and 
(2)    Basalt, a dark and slightly denser igneous rock (commonly erupted from volcanoes) in the lower part. Basalt appears to make up nearly all of the oceanic crust.
•    The Earth's crust is broken into many pieces known as plates. The plates "float" on the soft, plastic mantle beneath the crust. These plates move along smoothly most of the time, but they can get stuck and build up pressure. The rock bends until it snaps as the pressure builds. When this happens, an earthquake happens!
•    The ocean plates' basaltic rocks are much denser and heavier than the continental plates' granitic rocks. The continents ride on the denser oceanic plates as a result of this. 
•    The Lithosphere is a zone of rigid, brittle rock formed by the crust and the upper layer of the mantle. The Asthenosphere is a layer of asphalt-like consistency beneath the rigid lithosphere (Plastic in nature). 


•    The mantle is the part of the interior that lies beneath the crust. From Moho's discontinuity to a depth of 2,900 km, the mantle extends. The Asthenosphere is the uppermost layer of the mantle. Astheno is a Greek word that means "weak." It is estimated to be 400 kilometres long. 
•    During volcanic eruptions, it is the primary source of magma that makes its way to the surface. Its density (3.4 g/cm3) is higher than that of the crust. The lithosphere is made up of the crust and the uppermost part of the mantle. Its thickness varies between 10 and 200 kilometres. The asthenosphere extends beyond the lower mantle. It is in a state of solidity.
•    The mantle is the mostly solid interior of the Earth. Between Earth's dense, super-heated core and its thin outer layer, the crust, is the mantle. The Earth's mantle is about 2,900 kilometres (1,802 miles) thick and accounts for 84 per cent of the planet's total volume. It is mostly made up of olivine-rich dense rocks. 
•    The majority of the rocks that make up the Earth's mantle are silicates, which are a group of compounds with a silicon and oxygen structure. Olivine, garnet, and pyroxene are common silicates found in the mantle.
•    Magnesium oxide is the other major type of rock found in the mantle. Iron, aluminium, calcium, sodium, and potassium are some of the other elements found in the mantle. 
•    The temperature of the mantle ranges from 1000° Celsius (1832° Fahrenheit) near the crust's boundary to 3700° Celsius (6692° Fahrenheit) near the core's boundary. Heat and pressure in the mantle generally increase with depth. The mantle's heat and material transfer helps to shape the Earth's landscape.
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•    Plate tectonics is driven by mantle activity, which results in volcanoes, seafloor spreading, earthquakes, and orogeny (mountain-building). The asthenosphere is the upper portion of the mantle that extends up to 400 kilometres. It is the primary source of magma, with a density greater than that of the crust. The outer and inner mantles are separated by the Repetti discontinuity. The asthenosphere extends beyond the lower mantle. It is in a state of solidity.


•    The earth's core is located beneath the mantle and was discovered by R. D. Oldham in 1906 after a study of earthquake records. 
•    The core is divided into two parts: an outer and an inner part. At a depth of 2,900 kilometres, the core-mantle boundary is found. 
•    The outer core is in the state of liquid, while the inner core is in the state of solid. The density of material at the mantle core boundary is around 5 g/cm3, while it is around 13 g/cm3 at the earth's core at 6,300 km. 
•    The core is made up of extremely dense material, primarily nickel and iron. The nife layer is a term used to describe this layer.
•    The earth's core makes up 16% of its total volume. The mineral materials in the core are the heaviest and densest. Its outer boundary is 2,890 kilometres (1,800 miles) below the surface of the Earth. The transition between the inner and outer cores is about 5,000 kilometres (3,100 miles) beneath the surface of the Earth.
•    The temperature of the outer core varies from 4400 degrees Celsius near the outer core to 6100 degrees Celsius near the inner core. The Earth's magnetic field is thought to be influenced by eddy currents in the nickel-iron fluid of the outer core.
•    Without the outer core, life on Earth would be very different. The average magnetic field strength in the Earth's outer core was measured to be 25 Gauss, which is 50 times stronger than the magnetic field at the surface. 
•    The Earth's magnetic field is created by the convection of liquid metals in the outer core. This magnetic field stretches thousands of kilometres outward from the Earth, creating a protective bubble around the planet that deflects the Sun's solar wind.
•    Seismology has revealed that the Earth's inner core is a solid sphere with a radius of 1,216 km (760 mi), or roughly 70% that of the Moon. It's thought to be an iron–nickel alloy with a temperature of around 5778 K (5505 °C), which is very close to the Sun's surface.

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