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Aug 1, 2023 · The four main layers of the Earth are the crust, mantle, outer core, and inner core. The Earth, like an onion, consists of several concentric layers, each with its own unique set of properties and characteristics. The four primary layers are the crust, the mantle, the outer core, and the inner core. However, geologists subdivide these layers ...
- Overview
- The outer shell
Earth’s outermost, rigid, rocky layer is called the crust. It is composed of low-density, easily melted rocks; the continental crust is predominantly granitic rock (see granite), while composition of the oceanic crust corresponds mainly to that of basalt and gabbro. Analyses of seismic waves, generated by earthquakes within Earth’s interior, show that the crust extends about 50 km (30 miles) beneath the continents but only 5–10 km (3–6 miles) beneath the ocean floors.
At the base of the crust, a sharp change in the observed behaviour of seismic waves marks the interface with the mantle. The mantle is composed of denser rocks, on which the rocks of the crust float. On geologic timescales, the mantle behaves as a very viscous fluid and responds to stress by flowing. Together the uppermost mantle and the crust act mechanically as a single rigid layer, called the lithosphere.
The lithospheric outer shell of Earth is not one continuous piece but is broken, like a slightly cracked eggshell, into about a dozen major separate rigid blocks, or plates. There are two types of plates, oceanic and continental. An example of an oceanic plate is the Pacific Plate, which extends from the East Pacific Rise to the deep-sea trenches bordering the western part of the Pacific basin. A continental plate is exemplified by the North American Plate, which includes North America as well as the oceanic crust between it and a portion of the Mid-Atlantic Ridge. The latter is an enormous submarine mountain chain that extends down the axis of the Atlantic basin, passing midway between Africa and North and South America.
The lithospheric plates are about 60 km (35 miles) thick beneath the oceans and 100–200 km (60–120 miles) beneath the continents. (It should be noted that these thicknesses are defined by the mechanical rigidity of the lithospheric material. They do not correspond to the thickness of the crust, which is defined at its base by the discontinuity in seismic wave behaviour, as cited above.) They ride on a weak, perhaps partially molten, layer of the upper mantle called the asthenosphere. Slow convection currents deep within the mantle generated by radioactive heating of the interior drive lateral movements of the plates (and the continents on top of them) at a rate of several centimetres per year. The plates interact along their margins, and these boundaries are classified into three general types on the basis of the relative motions of the adjacent plates: divergent, convergent, and transform (or strike-slip).
In areas of divergence, two plates move away from each other. Buoyant upwelling motions in the mantle force the plates apart at rift zones (such as along the middle of the Atlantic Ocean floor), where magmas from the underlying mantle rise to form new oceanic crustal rocks.
Lithospheric plates move toward each other along convergent boundaries. When a continental plate and an oceanic plate come together, the leading edge of the oceanic plate is forced beneath the continental plate and down into the asthenosphere—a process called subduction. Only the thinner, denser slabs of oceanic crust will subduct, however. When two thicker, more buoyant continents come together at convergent zones, they resist subduction and tend to buckle, producing great mountain ranges. The Himalayas, along with the adjacent Plateau of Tibet, were formed during such a continent-continent collision, when India was carried into the Eurasian Plate by relative motion of the Indian-Australian Plate.
Earth’s outermost, rigid, rocky layer is called the crust. It is composed of low-density, easily melted rocks; the continental crust is predominantly granitic rock (see granite), while composition of the oceanic crust corresponds mainly to that of basalt and gabbro. Analyses of seismic waves, generated by earthquakes within Earth’s interior, show that the crust extends about 50 km (30 miles) beneath the continents but only 5–10 km (3–6 miles) beneath the ocean floors.
At the base of the crust, a sharp change in the observed behaviour of seismic waves marks the interface with the mantle. The mantle is composed of denser rocks, on which the rocks of the crust float. On geologic timescales, the mantle behaves as a very viscous fluid and responds to stress by flowing. Together the uppermost mantle and the crust act mechanically as a single rigid layer, called the lithosphere.
The lithospheric outer shell of Earth is not one continuous piece but is broken, like a slightly cracked eggshell, into about a dozen major separate rigid blocks, or plates. There are two types of plates, oceanic and continental. An example of an oceanic plate is the Pacific Plate, which extends from the East Pacific Rise to the deep-sea trenches bordering the western part of the Pacific basin. A continental plate is exemplified by the North American Plate, which includes North America as well as the oceanic crust between it and a portion of the Mid-Atlantic Ridge. The latter is an enormous submarine mountain chain that extends down the axis of the Atlantic basin, passing midway between Africa and North and South America.
The lithospheric plates are about 60 km (35 miles) thick beneath the oceans and 100–200 km (60–120 miles) beneath the continents. (It should be noted that these thicknesses are defined by the mechanical rigidity of the lithospheric material. They do not correspond to the thickness of the crust, which is defined at its base by the discontinuity in seismic wave behaviour, as cited above.) They ride on a weak, perhaps partially molten, layer of the upper mantle called the asthenosphere. Slow convection currents deep within the mantle generated by radioactive heating of the interior drive lateral movements of the plates (and the continents on top of them) at a rate of several centimetres per year. The plates interact along their margins, and these boundaries are classified into three general types on the basis of the relative motions of the adjacent plates: divergent, convergent, and transform (or strike-slip).
In areas of divergence, two plates move away from each other. Buoyant upwelling motions in the mantle force the plates apart at rift zones (such as along the middle of the Atlantic Ocean floor), where magmas from the underlying mantle rise to form new oceanic crustal rocks.
Lithospheric plates move toward each other along convergent boundaries. When a continental plate and an oceanic plate come together, the leading edge of the oceanic plate is forced beneath the continental plate and down into the asthenosphere—a process called subduction. Only the thinner, denser slabs of oceanic crust will subduct, however. When two thicker, more buoyant continents come together at convergent zones, they resist subduction and tend to buckle, producing great mountain ranges. The Himalayas, along with the adjacent Plateau of Tibet, were formed during such a continent-continent collision, when India was carried into the Eurasian Plate by relative motion of the Indian-Australian Plate.
- Crust. Temperature: 475 K (∼200°C) at the surface to 1300 K (∼1000°C) Thickness: 25 miles (32 km) for continental crust and 3-5 miles (8 km) for oceanic crust.
- Upper Mantle. Temperature: 1200 K (∼ 932°C) at the upper boundary with the crust to 1900 K (∼1652 °C) at the boundary with the lower mantle. Thickness: 255 miles (410 km)
- Lower Mantle. Temperature: 1900 K (∼ 1600°C) in the outer regions which can reach up to 4300 K (∼4000°C) at the bottom. Thickness: 1,400 miles (2,250 km)
- Outer Core. Temperature: 4,300 K (4,030°C) in the outer regions to 6,000 K (5,730°C) closest to the inner core. Thickness: 1,355 miles (2,180 km) Density: 9,900 – 12,200 kg/m3.
Apr 25, 2024 · Subjects. “ Crust ” describes the outermost shell of a terrestrial planet. Our planet ’s thin, 40-kilometer (25-mile) deep crust—just 1 percent of Earth ’s mass—contains all known life in the universe. Earth has three layers: the crust, the mantle, and the core. The crust is made of solid rocks and minerals.
Sep 21, 2023 · The lithosphere is the rigid, outermost, rocky shell of the Earth. It is composed of the crust and the top part of the mantle, called the lithospheric mantle. This extends around 40 to 280 ...
- Founding Editor
Dec 15, 2020 · The earth is split into four major layers: the crust, the mantle, the outer core and the inner core. The crust is what humans live on, and it consists of only one percent of the Earth's mass. The centre of the Earth is a solid ball of nickel and iron roughly 70% the size of the moon. Geologists have come a long way in terms of the collective ...
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Aug 8, 2023 · The inner core is the deepest layer and has a solid inner core and a liquid outer core with a temperature range of 4400 °C to 6100 °C (7,952 °F to 11,012 °F). The outermost layer is the crust, which is mostly composed of basalt and granite. Therefore, there are only four layers of the Earth.
