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Internal Structure of Earth Notes

Earth's Internal Structure - Crust Mantle Core

» Earth is made up of several different layers, each with unique properties.
» The interior structure of the Earth is layered in spherical shells, like an onion.
» These layers can be defined by their chemical and their rheological properties.
» Three centuries ago, the English scientist Isaac Newton calculated, from his studies of planets and the force of gravity, that the average density of the Earth is twice that of surface rocks and therefore that the Earth's interior must be composed of much denser material.
» Earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core.
» The boundaries between these layers were discovered by seismographs which showed the way vibrations bounced off the layers during earthquakes. Between the Earth's crust and the mantle is a boundary called the moho. It was the first discovery of a major change in the Earth's structure as one goes deeper.
» Scientific understanding of the internal structure of the Earth is based on observations of topography and bathymetry, observations of rock in outcrop, samples brought to the surface from greater depths by volcanoes or volcanic activity, analysis of the seismic waves that pass through the Earth, measurements of the gravitational and magnetic fields of the Earth, and experiments with crystalline solids at pressures and temperatures characteristic of the Earth's deep interior.
» The planet Earth is made up of three main shells: the very thin, brittle crust, the mantle, and the core; the mantle and core are each divided into two parts

Depth of Different Layer of Earth's

Depth
Layer
Kilometres
Miles
0–35
0–22
Crust (locally varies between 5 and 70 km)
35–2,890
22–1,790
Mantle
210-270
130-168
… Upper mesosphere (upper mantle)
660–2,890
410–1,790
… Lower mesosphere (lower mantle)
2,890–5,150
1,790–3,160
Outer core
5,150–6,360
3,160–3,954
Inner core


Layers of Earth

» Earth’s interior is composed of 4 layers: 3 solid and 1 liquid
1.   Crust (Solid)
2.   Mantle (Solid)
3.   Outer Core (Solid)
4.   Inner Core (Liquid)

The Crust


» Because the crust is accessible to us, its geology has been extensively studied, and therefore much more information is known about its structure and composition than about the structure and composition of the mantle and core.
» The crust ranges from 5–70 kilometres (3.1–43.5 mi) in depth and is the outermost layer. The thin parts are the oceanic crust, which underlies the ocean basins (5–10 km) and is composed of dense (mafic) iron magnesium silicate igneous rocks, like basalt. The thicker crust is the continental crust, which is less dense and composed of (felsicsodium potassium aluminium silicate rocks, like granite.
» Major constituent elements of crust are Silica (Si) and Aluminium (Al) and thus, it is often termed as SIAL (Sometimes SIAL is used to refer Lithosphere, which is the region comprising the crust and uppermost solid mantle, also).
» The mean density of the materials in the crust is 3g/cm3.
» The discontinuity between the hydrosphere and crust is termed as the Conrad Discontinuity.
» The boundary between the crust and mantle is called the Mohorovicic discontinuity (or Moho); it is named in honour of the man who discovered it, the Croatian scientist Andrija Mohorovicic. No one has ever seen this boundary, but it can be detected by a sharp increase downward in the speed of earthquake waves there.
The crust is the outermost layer of the Earth. It is made of solid rocks. It is mostly made of the lighter elements, siliconoxygenaluminium. Because of this, it is known as sial (silicon = Si; aluminium = Al) or felsic.

The Mantle


» Earth's mantle extends to a depth of 2,890 km, making it the thickest layer of Earth.
» The mantle is divided into upper and lower mantle. The upper and lower mantle are separated by the transition zone. The lowest part of the mantle next to the core-mantle boundary is known as the D″ (pronounced dee-double-prime) layer.
» It has different temperatures at different depths. The temperature is lowest immediately beneath the crust and increases with depth. The highest temperatures occur where the mantle material is in contact with the heat-producing core.
» This steady increase of temperature with depth is known as the geothermal gradient.
» The major constituent elements of the mantle are Silicon and Magnesium and hence it is also termed as SIMA.
» The density of the layer is higher than the crust and varies from 3.3 – 5.4g/cm3.
» The uppermost solid part of the mantle and the entire crust constitute the Lithosphere.
» The discontinuity between the upper mantle and the lower mantle is known as Repetti Discontinuity.
» The mantle is the layer of the Earth right below the crust. It is made mostly of oxygen, silicon and the heavier element magnesium.
» It is known as sima (Si for silicon + ma for magnesium) or mafic.
» The mantle itself is divided into layers.
» The uppermost part of the mantle is solid and forms the base of the crust. It is made of the heavy rock peridotite. The continental and oceanic plates include both the crust proper and this uppermost solid layer of the mantle. Together this mass makes up the lithosphere.
» The lithosphere plates float on the semi-liquid asthenosphere below.
1.   Upper aesthenospheremagma
2.   Lower aesthenosphere
3.   Lower mantle


The Core


» Earth has a core, but this is really two distinct parts: the inner core and the outer core.
» Both parts of the core are made up of mostly iron and some nickel.
» The difference is that in the inner core, those minerals are solid and in the outer core, they're liquid.
» The average density of Earth is 5,515 kg/m3. Because the average density of the surface material is only around 3,000 kg/m3, we must conclude that denser materials exist within Earth's core.
» Seismic measurements show that the core is divided into two parts, a "solid" inner core with a radius of ≈1,220 km and a liquid outer core extending beyond it to a radius of ≈3,400 km.
» The densities are between 9,900 and 12,200 kg/m3 in the outer core and 12,600–13,000 kg/m3 in the inner core.
» It is composed mainly of iron (Fe) and nickel (Ni) and hence it is also called as NIFE.
» The core constitutes nearly 15% of earth’s volume and 32.5% of earth’s mass.
» The core is the densest layer of the earth with its density ranges between 9.5-14.5g/cm3.
» The Earth's core is made of solid iron and nickel and is about 5000–6000oC.
» Outer core is a liquid layer below the mantle,
» Inner core is the very centre of the Earth. It is very hot and, due to the high pressure, it is solid.
» The discontinuity between the upper core and the lower core is called as Lehmann Discontinuity.



1.The density of the inner core of the earth is high due to?
[A] More iron
[B] Less Nickel
[C] Less Silicon
[D] All of above
Answer: B. Less Nickel


2.The outer core of the earth is in molten condition due to?
[A] Less pressure than inner core
[B] Magnesium
[C] basalt
[D] Granite
Answer: A. Less pressure than inner core


3.The inner core of the earth is in solid state due to?
[A] Heavy temperature
[B] Heavy pressure
[C] Basalt rocks
[D] a and b
Answer: D. a and b


4.The temperature in the inner core of the earth is?
[A] 3000 degree c
[B] 4000 degree c
[C] 5000 degree c
[D] 6000 degree c
Answer: D. 6000 degree c


5.The thickness of the inner solid core is?
[A] 900 kms
[B] 3000 kms
[C] 2600 kms
[D] 1220 kms
Answer: D. 1220 kms


6.The thickness of the outer liquid core is?
[A] 1000 kms
[B] 2200 kms
[C] 500 kms
[D] 1800 kms
Answer: B. 2200 kms


7.The core of the earth contains layers called?
[A] Outer Core
[B] Inner Core
[C] Mantle
[D] a and b
Answer: B. Inner Core


8.Mantle of the earth comprises?
[A] Iron and Magnesium
[B] Nickel
[C] Granite
[D] All of above
Answer: A. Iron and Magnesium


9.The rocks present in the crust of the earth are?
[A] Granite
[B] Basalt
[C] a and b
[D] Nickle
Answer: C. a and b


10.Which of the following is the middle layer of the earth?
[A] Core
[B] Mantle
[C] Crust
[D] Basalt
Answer: B. Mantle
11.The thickness of crust under continents is?
[A] 40-100 kms
[B] 35-60 kms
[C] 80-100 kms
[D] 50-100 kms
Answer: B. 35-60 kms


12.The thickness of crust under oceans is?
[A] 10-15 kms
[B] 60-160 kms
[C] 5-12 kms
[D] 30-100 kms
Answer: C. 5-12 kms


13.The outer layer of the earth is called?
[A] Mantle
[B] Crust
[C] Core
[D] Magma
Answer: B. Crust


14.What are the layers in the interior of the earth?
[A] Crust
[B] Mantle
[C] Core
[D] All the above
Answer: D. All the above

Frequently asked questions:

How do we know about the internal structure of the earth?

Most of what we know about the interior of the Earth comes from the study of seismic waves from earthquakes. Seismic waves from large earthquakes pass throughout the Earth. These waves contain vital information about the internal structure of the Earth.

What is the percentage of iron in the chemical composition of Earth?

Fresh water exists in liquid form in lakes and rivers and as water vapour in the atmosphere, which causes much of Earth's weather. Earth's crust is made up of several elements: oxygen, 47 percent; silicon, 27 percent; aluminium, 8 percent; iron, 5 percent; calcium, 4 percent; magnesium, potassium and sodium, 2 percent.


What are the layers of the Earth and describe each?

Earth can be divided into three main layers: the core, the mantle and the crust.Each of these layers can be further divided into two parts: the inner and outer core, the upper and lower mantle and the continental and oceanic crust. Both the inner and outer core are made up of mostly iron and a little bit of nickel.

What is the structure of the earth?

The interior structure of the Earth is layered in spherical shells, like an onion. These layers can be defined by their chemical and their rheological properties. Earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core.

How deep is the earth's crust?

The Earth's radius is about 4,000 miles (6,400 kilometres). The main layers of its interior are in descending order: crust, mantle and core. The crust thickness averages about 18 miles (30 kilometres) under the continents, but is only about 3 miles (5 kilometres) under the oceans.

What is the most abundant element in the earth?

Hydrogen is more plentiful than any other element, making up about 3/4 the mass of the universe. Helium is second, making up almost all of the remaining 25%.Oxygen is a distant third. On earth, oxygen is the most common element, making up about 47% of the earth's mass.

See also:

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