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Structure of Earth

The Earth’s structure is a fascinating and complex arrangement of layers that make up our planet’s interior. Understanding this structure is crucial for geologists and scientists as it provides insights into the Earth’s composition, behavior, and the processes that shape our planet. This knowledge is also essential for various fields, including geology, seismology, and plate tectonics , as it helps explain natural phenomena like earthquakes , volcanoes , and the formation of continents and ocean basins.

Interior of the Earth: Crust, Mantle and Core

What should you understand about the interior of the earth, sources of information about the interior of the earth, structure of the earth’s interior, composition of earth, temperature, pressure and density of the earth’s interior, temperature, earth’s magnetic field.

The Earth’s interior can be divided into three main layers: the crust, the mantle, and the core. These layers have distinct properties and compositions, which play a significant role in shaping our planet’s geology and behavior.

• The Earth’s crust is the outermost layer and the one we interact with directly. It varies in thickness, with oceanic crust being thinner (about 4-7 miles or 6-11 kilometers) and continental crust being thicker (averaging about 19 miles or 30 kilometers).
• The crust is primarily composed of solid rock, with different types of rock prevailing in continental and oceanic regions. Continental crust is mostly made up of granitic rocks , while oceanic crust is primarily composed of basaltic rocks.
• The Earth’s crust is where we find the Earth’s landforms , such as mountains, valleys, and plains, as well as the ocean floor.
• The mantle is located beneath the Earth’s crust and extends to a depth of about 1,800 miles (2,900 kilometers). It is the thickest layer of the Earth.
• The mantle is composed of solid rock, primarily silicate minerals . Although it is solid, the mantle behaves like a very viscous or plastic material over geological timescales. This property allows the mantle to flow slowly, leading to the movement of tectonic plates and the associated geological phenomena like earthquakes and volcanoes.
• The heat generated from the Earth’s interior and the decay of radioactive elements contribute to the high temperatures within the mantle.
• The Earth’s core is divided into two parts: the outer core and the inner core.
• The outer core is located beneath the mantle, beginning at a depth of about 1,800 miles (2,900 kilometers) and extending to around 3,500 kilometers below the surface.
• It is primarily composed of molten iron and nickel . The high temperatures and pressures in the outer core keep these materials in a liquid state.
• The motion of molten iron in the outer core is responsible for generating the Earth’s magnetic field through the geodynamo process.
• The inner core is situated at the very center of the Earth, starting at a depth of about 3,500 kilometers.
• It is primarily composed of solid iron and nickel. Despite the extremely high temperatures at this depth, the inner core remains solid due to the tremendous pressure.
• The inner core’s solid nature is important for understanding the Earth’s internal dynamics, including how seismic waves pass through it.

The Earth’s structure and the interactions between these layers are responsible for various geological phenomena, including earthquakes, volcanic eruptions, and the movement of tectonic plates. The knowledge of the Earth’s interior structure is crucial for understanding and predicting these natural events, as well as for exploring the planet’s history and geology.

• It is not possible to know about the earth’s interior by direct observations because of the huge size and the changing nature of its interior composition.
• It is an almost impossible distance for the humans to reach till the centre of the earth (The earth’s radius is 6,370 km).
• Through mining and drilling operations we have been able to observe the earth’s interior directly only up to a depth of few kilometers.
• The rapid increase in temperature below the earth’s surface is mainly responsible for setting a limit to direct observations inside the earth.
• But still, through some direct and indirect sources, the scientists have a fair idea about how the earth’s interior look like.

Direct Sources:

• Rocks from mining area
• Volcanic eruptions

Indirect Sources

• By analyzing the  rate of change of temperature and pressure  from the surface towards the interior.
• Meteors , as they belong to the same type of materials earth is made of.
• Gravitation , which is greater near poles and less at the equator.
• Gravity anomaly , which is the change in gravity value according to the mass of material, gives us information about the materials in the earth’s interior.
• Magnetic sources .
• Seismic Waves : the shadow zones of body waves (Primary and secondary waves) give us information about the state of materials in the interior.

Structure of earth’s interior is fundamentally divided into three layers –  crust, mantle and core .

• It is the outermost solid part of the earth, normally about 8-40 kms thick.
• It is brittle in nature.
• Nearly 1% of the earth’s volume and 0.5% of earth’s mass are made of the crust.
• The thickness of the crust under the oceanic and continental areas are different. Oceanic crust is thinner (about 5kms) as compared to the continental crust (about 30kms).
• 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 portion of the interior beyond the crust is called as the mantle.
• The discontinuity between the  crust and mantle  is called as the  Mohorovich Discontinuity or Moho discontinuity.
• The mantle is about 2900kms in thickness.
• Nearly 84% of the earth’s volume and 67% of the earth’s mass is occupied by the mantle.
• 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  asthenosphere  (in between 80-200km) is a highly viscous, mechanically weak and ductile,  deforming region of the upper mantle which lies just below the lithosphere.
• The asthenosphere is the main source of magma and it is the layer over which the lithospheric plates/ continental plates move (plate tectonics).
• The discontinuity between the  upper mantle and the lower mantle  is known as  Repetti Discontinuity .
• The portion of the mantle which is just below the lithosphere and asthenosphere, but above the core is called as  Mesosphere .
• It is the innermost layer surrounding the earth’s centre.
• The  core is separated from the mantle by Guttenberg’s Discontinuity .
• 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 Core consists of two sub-layers: the inner core and the outer core.
• The inner core is in solid state and the outer core is in the liquid state (or semi-liquid).
• The discontinuity between the upper core and the lower core is called as  Lehmann Discontinuity.
• Barysphere  is sometimes used to refer the core of the earth or sometimes the whole interior.

Major Elements and Minerals in Earth’s Composition:

• Oxygen (O): Oxygen is the most abundant element in Earth’s composition, making up approximately 46.6% of the Earth’s crust by weight. It is a crucial component of minerals and compounds, such as silicates and oxides.
• Silicon (Si): Silicon is the second most abundant element in the Earth’s crust, accounting for about 27.7% of its composition. It is a key component in various silicate minerals, which are the primary building blocks of the Earth’s crust.
• Aluminum (Al): Aluminum makes up around 8.1% of the Earth’s crust. It is often found in minerals like feldspar , bauxite , and various silicates.
• Iron (Fe): Iron is another essential element in Earth’s composition, constituting approximately 5% of the Earth’s crust. It is found in various minerals, including hematite and magnetite .
• Calcium (Ca): Calcium makes up about 3.6% of the Earth’s crust and is commonly found in minerals like calcite and gypsum .
• Sodium (Na) and Potassium (K): Sodium and potassium together account for around 2.8% of the Earth’s crust. These elements are typically found in minerals like feldspar.
• Magnesium (Mg): Magnesium constitutes about 2.1% of the Earth’s crust and is found in minerals such as olivine and serpentine .
• Titanium (Ti): Titanium makes up approximately 0.57% of the Earth’s crust and is present in minerals like ilmenite and rutile .
• Hydrogen (H): While hydrogen is not a major component of the Earth’s crust, it is a significant element in the Earth’s overall composition, mainly in the form of water (H2O).
• Other Elements: Various other elements, including sulfur , carbon, phosphorus, and many trace elements, are present in smaller amounts in the Earth’s composition.

Distribution of Elements Within Earth’s Layers:

• Crust: The Earth’s crust is primarily composed of silicate minerals, including quartz , feldspar, mica , and various types of rock. Silicon and oxygen are the most abundant elements in the crust, forming the backbone of these minerals.
• Mantle: The mantle is composed mainly of silicate minerals, with iron and magnesium as dominant elements. Olivine, pyroxenes, and garnet are common minerals found in the mantle.
• Outer Core: The outer core is primarily composed of liquid iron and nickel. This layer is responsible for generating Earth’s magnetic field, with iron being the dominant element.
• Inner Core: The inner core is composed of solid iron and nickel. Despite the extremely high temperatures, the intense pressure keeps these elements in a solid state.

The distribution of elements within Earth’s layers is a result of the differentiation and separation of materials during the Earth’s early history. The layered structure of the Earth is a consequence of the physical and chemical processes that have occurred over billions of years, including planetary accretion, differentiation, and geological activity.

• A rise in temperature with increase in depth is observed in mines and deep wells.
• These evidence along with molten lava erupted from the earth’s interior supports that the temperature increases towards the centre of the earth.
• The different observations show that the rate of increase of temperature is not uniform from the surface towards the earth’s centre. It is faster at some places and slower at other places.
• In the beginning, this rate of increase of temperature is at an average rate of 1C for every 32m increase in depth.
• While in the upper 100kms, the increase in temperature is at the rate of 12C per km and in the next 300kms, it is 20C per km. But going further deep, this rate reduces to mere 10C per km.
• Thus, it is assumed that the  rate of increase of temperature beneath the surface is decreasing   towards the centre  (do not confuse rate of increase of temperature with increase of temperature.  Temperature is always increasing from the earth’s surface towards the centre ).
• The temperature at the centre is estimated to lie somewhere between 3000C and 5000C, may be that much higher due to the chemical reactions under high-pressure conditions.
• Even in such a high temperature also, the materials at the centre of the earth are in solid state because of the heavy pressure of the overlying materials.
• Just like the temperature, the  pressure is also increasing from the surface towards the centre  of the earth.
• It is due to the huge weight of the overlying materials like rocks.
• It is estimated that in the deeper portions, the pressure is tremendously high which will be nearly 3 to 4 million times more than the pressure of the atmosphere at sea level.
• At high temperature, the materials beneath will melt towards the centre part of the earth but due to heavy pressure, these molten materials acquire the properties of a solid and are probably in a plastic state.
• Due to increase in pressure and presence of heavier materials like Nickel and Iron towards the centre, the  density of earth’s layers also gets on increasing towards the centre .
• The average density of the layers gets on increasing from crust to core and it is nearly 14.5g/cm3 at the very centre.

Earth’s magnetic field is a crucial and complex feature that surrounds our planet. It plays a significant role in our daily lives and has several important functions. Here’s an overview of Earth’s magnetic field:

1. Generation of Earth’s Magnetic Field:

• Earth’s magnetic field is primarily generated by the movement of molten iron and nickel in the outer core of the planet. This process is known as the geodynamo.
• The geodynamo is driven by the heat generated from the decay of radioactive isotopes in the Earth’s interior and the cooling of the core.

2. Magnetic Polarity:

• Earth’s magnetic field has a north and south magnetic pole, similar to a bar magnet. However, these magnetic poles are not aligned with the geographic North and South Poles.
• The positions and orientations of Earth’s magnetic poles can change over geological time, and these reversals in polarity are recorded in rocks as “magnetic striping.”

3. Magnetic Field Components:

• Earth’s magnetic field is characterized by its strength, inclination, and declination.
• Magnetic Strength: This represents the intensity of the magnetic field at a specific location on Earth’s surface.
• Inclination: It refers to the angle at which the magnetic field lines intersect the Earth’s surface, varying from near-vertical at the magnetic poles to horizontal at the equator.
• Declination: This is the angle between true north (geographic north) and magnetic north.

4. Magnetic Field Function and Importance:

• It serves as a protective shield, deflecting harmful charged particles from the Sun, such as solar wind and cosmic rays. This shield is known as the magnetosphere and helps protect the atmosphere and life on Earth.
• It enables navigation and orientation for migratory animals, including birds and sea turtles, that use the magnetic field as a compass.
• Compasses rely on Earth’s magnetic field for navigation and orientation.
• The magnetic field is used in various scientific and geological studies, including paleomagnetism (the study of ancient magnetic fields recorded in rocks) to understand Earth’s history and the movement of tectonic plates.
• The magnetic field is essential for modern technology, including magnetic resonance imaging (MRI) in medicine and various applications in geophysical exploration.

5. Changes in Earth’s Magnetic Field:

• The Earth’s magnetic field is not constant and can undergo changes over time, including secular variation (gradual changes) and geomagnetic reversals (flips in magnetic polarity).
• Researchers monitor these changes, and recent observations have shown that the magnetic North Pole is shifting at a faster rate than in the past.

Understanding Earth’s magnetic field is essential for various scientific, technological, and environmental reasons. It is an integral part of the planet’s geology and plays a vital role in maintaining the conditions necessary for life on Earth.

Jijo Sudarsan  , Interior of the Earth: Crust, Mantle and Core(2018) ,https://www.clearias.com/interior-of-the-earth/

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Interior of the Earth: Crust, Mantle and Core

Last updated on September 20, 2023 by ClearIAS Team

Table of Contents

What should you understand about the interior of the earth?

• It is not possible to know about the earth’s interior by direct observations because of the huge size and the changing nature of its interior composition.
• It is an almost impossible distance for the humans to reach till the centre of the earth (The earth’s radius is 6,370 km).
• Through mining and drilling operations we have been able to observe the earth’s interior directly only up to a depth of few kilometers.
• The rapid increase in temperature below the earth’s surface is mainly responsible for setting a limit to direct observations inside the earth.
• But still, through some direct and indirect sources, the scientists have a fair idea about how the earth’s interior look like.

Sources of Information about the interior of the earth

Direct sources:.

• Rocks from mining area
• Volcanic eruptions

Indirect Sources

• By analyzing the rate of change of temperature and pressure from the surface towards the interior.
• Meteors , as they belong to the same type of materials earth is made of.
• Gravitation , which is greater near poles and less at the equator.
• Gravity anomaly , which is the change in gravity value according to the mass of material, gives us information about the materials in the earth’s interior.
• Magnetic sources .
• Seismic Waves : the shadow zones of body waves ( Primary and secondary waves ) give us information about the state of materials in the interior.

Structure of the earth’s interior

Structure of earth’s interior is fundamentally divided into three layers – crust, mantle and core .

• It is the outermost solid part of the earth, normally about 8-40 kms thick.
• It is brittle in nature.
• Nearly 1% of the earth’s volume and 0.5% of earth’s mass are made of the crust.
• The thickness of the crust under the oceanic and continental areas are different. Oceanic crust is thinner (about 5kms) as compared to the continental crust (about 30kms).
• 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 portion of the interior beyond the crust is called as the mantle.
• The discontinuity between the crust and mantle is called as the Mohorovich Discontinuity or Moho discontinuity.
• The mantle is about 2900kms in thickness.
• Nearly 84% of the earth’s volume and 67% of the earth’s mass is occupied by the mantle.
• 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 asthenosphere (in between 80-200km) is a highly viscous, mechanically weak and ductile,  deforming region of the upper mantle which lies just below the lithosphere.
• The asthenosphere is the main source of magma and it is the layer over which the lithospheric plates/ continental plates move ( plate tectonics ).

• The discontinuity between the upper mantle and the lower mantle is known as Repetti Discontinuity .
• The portion of the mantle which is just below the lithosphere and asthenosphere, but above the core is called as Mesosphere .
• It is the innermost layer surrounding the earth’s centre.
• The core is separated from the mantle by Guttenberg’s Discontinuity .
• 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 Core consists of two sub-layers: the inner core and the outer core.
• The inner core is in solid state and the outer core is in the liquid state (or semi-liquid).
• The discontinuity between the upper core and the lower core is called as Lehmann Discontinuity.
• Barysphere is sometimes used to refer the core of the earth or sometimes the whole interior.

Temperature, Pressure and Density of the Earth’s Interior

Temperature.

• A rise in temperature with increase in depth is observed in mines and deep wells.
• These evidence along with molten lava erupted from the earth’s interior supports that the temperature increases towards the centre of the earth.
• The different observations show that the rate of increase of temperature is not uniform from the surface towards the earth’s centre. It is faster at some places and slower at other places.
• In the beginning, this rate of increase of temperature is at an average rate of 1 0 C for every 32m increase in depth.
• While in the upper 100kms, the increase in temperature is at the rate of 12 0 C per km and in the next 300kms, it is 20 0 C per km. But going further deep, this rate reduces to mere 10 0 C per km.
• Thus, it is assumed that the rate of increase of temperature beneath the surface is decreasing towards the centre (do not confuse rate of increase of temperature with increase of temperature. Temperature is always increasing from the earth’s surface towards the centre ).
• The temperature at the centre is estimated to lie somewhere between 3000 0 C and 5000 0 C, may be that much higher due to the chemical reactions under high-pressure conditions.
• Even in such a high temperature also, the materials at the centre of the earth are in solid state because of the heavy pressure of the overlying materials.
• Just like the temperature, the pressure is also increasing from the surface towards the centre of the earth.
• It is due to the huge weight of the overlying materials like rocks.
• It is estimated that in the deeper portions, the pressure is tremendously high which will be nearly 3 to 4 million times more than the pressure of the atmosphere at sea level.
• At high temperature, the materials beneath will melt towards the centre part of the earth but due to heavy pressure, these molten materials acquire the properties of a solid and are probably in a plastic state.
• Due to increase in pressure and presence of heavier materials like Nickel and Iron towards the centre, the density of earth’s layers also gets on increasing towards the centre .
• The average density of the layers gets on increasing from crust to core and it is nearly 14.5g/cm3 at the very centre.

Article by: Jijo Sudarsan

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Reader Interactions

July 12, 2016 at 10:15 pm

sir i prefer reading offline …but ur notes on each issue attract me …I know that ir geography nots and history and economics are oriented from nce rts as i m reading them mercylessely.BT IS THIS SO WITH UR CULTURE NOTES ALSO

July 12, 2016 at 10:19 pm

sir plz say me in order that i will convince myself that after reading 9-12 ncerts …ramesh sigh ….gc leong……nitin singhania…..shankar ias…..vipin chandra or spectrum….my core syllablus will complete and no need to see ur notes as …..i have problem in vision …and cant use internet more.

October 1, 2016 at 12:30 am

Well written in point wise. Thank you sir. If possible can u plz lso upload the physiography of india as wel as other topics specific to indian geography. Thank you

December 6, 2016 at 10:19 am

Most of the aspects related to the topic covered point-wise and enable students to score good marks. Great effort.

March 17, 2017 at 8:56 pm

why it is important to study changes going around and inside earth crust? answer this question?

December 9, 2017 at 6:56 pm

Yes good question…..now listen few things ,what if some tragedy will happen and you don’t know about your room that where is the gate or which corner is the safest ,you simply land yourself into trouble knowing about that room completely will help you out …in the same way knowing about the interior of the earth is essential to explore it for the good reason

January 8, 2022 at 1:10 pm

My doubt is when pressure is inversely proportional to the temperature then how at the center or the inner most point tends to have high temperature with extremely high pressure.

April 25, 2017 at 10:48 am

Thanks very helpful… And not confusing

November 7, 2017 at 2:36 am

Very nice answer

January 10, 2018 at 12:17 pm

Sir this note is very helpful to me.Please upload note on plate techtonic theory.

February 28, 2018 at 10:37 pm

very helpful notes sir.

May 20, 2018 at 2:50 pm

Nice answer Thank you sir

July 5, 2018 at 8:19 pm

Very good effort every important topic is cover

August 24, 2018 at 5:44 pm

I like It becouse This note gives by perfect knowledge Thank you fo that.

December 15, 2018 at 8:26 pm

Ashu sir you gave a very clear example

March 16, 2019 at 3:58 pm

What are the problems found in the upper mantle and the transition zone??

June 5, 2019 at 3:07 pm

Alex chettayiii

June 22, 2019 at 8:26 pm

Sir according to ncert the volume percentage of crust is 0.5%,mantel is 16%,and core is 83% so how urs mantel 85% and core 25% will be correct

June 30, 2021 at 9:53 pm

Actually, the volume of Crust is 1%, Mantle is 85% and lastly, the core is 15%

August 25, 2019 at 12:40 pm

Sir how to make notes from ncert ….Before making notes how many

times should I read??

And also tell me about your’s macroupsc syllabus whether I would make make notes from each every single point sir….

August 28, 2019 at 8:58 pm

Thickness of Mantle is less than half of the radius of Earth but it accounts for 84% of total volume of earth and 68% mass. How? If thickness of mantle is less than core then how come volume of mantle is more i.e 84%. Can anyone explain the relation between thickness and volume

April 2, 2021 at 10:27 pm

Earth is a Sphere, core is at its center and surrounded by the mantle, so…though the thickness of the mantle is equal or bit less(not much) than the core , the volume of mantle is gonna be more (cuz core is at the center of the sphere and mantle is away from the center). (Hope it is cleared to u, but still if u need further help just mail me, i’ll try to help u out with a diagram. email id: [email protected] )

April 3, 2020 at 1:15 pm

Is it enough to clear the main… or is it only for prelims??

April 10, 2020 at 4:23 pm

Only for Prelims

July 18, 2020 at 12:43 pm

what are the chemical composition of crust,mantleand core

December 12, 2020 at 11:16 am

really helpful thanks.

January 16, 2021 at 8:09 pm

This comment is regarding “mesosphere” . I have read different books but could not find the word mesosphere for upper and lower mantle. I guess it is pyrosphere dominant in basalt. Please rectify me if m wrong. Thank u

March 5, 2022 at 8:43 am

Best explanation

September 26, 2022 at 11:47 pm

In the 1st pic, there should be lithosphere🙏 and very greatful to get notes from Clear IAS team. Thank you soo much.

November 12, 2022 at 3:31 pm

I thought that the continental crust is made of silica and aluminum making up the SIAL and oceanic crust rocks are mainly composed of silica and magnesium forming the SIMA. PLEASE CHECK ON THIS AND MAKE CLARIFICATIONS INSTEAD OF GENERALISING THEM AS SIAL. THE COMPOSITION OF ROCKS DIFFERS BETWEEN THE TWO LAYERS OF THE CRUST. PLEASE I DO WELCOME CORRECTIONS AS WELL. WE LEARN FROM EACH OTHER

August 13, 2023 at 9:08 am

oceanic crust is made of Silica and magnesium(SiMa) is write for crust layer

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Interior of Earth, Sources of Information, Layers, Structure, Diagram

Interior of Earth is divided into 3 layers i.e Crust, Mantle and Core. Check more about Interior of Earth its Layers, Structure and Diagram for UPSC Exam.

Table of Contents

Interior of Earth

Earth has different layers based on what they are made of and their physical properties. The main layers are the core, mantle, and crust. In terms of mechanical properties, they include the lithosphere, asthenosphere, lower mantle, outer core, and inner core.

At the very center of the Earth is the inner core, which is solid iron and about  1221 kilometers wide. It is extremely hot, with temperatures as high as the surface of the sun (around 5200°C) but the immense pressure keeps it solid. The heat comes from the decay of radioactive elements, leftover heat from when the planet formed, and heat from the outer core solidifying. The inner core rotates in the same direction as the Earth’s surface, but slightly faster, completing an extra rotation every 1000 years or so.

Sources of Information about the Earth’s Interior

There are mainly two types of sources that give information about the interior of the Earth i.e. Direct sources and indirect sources.

Diagram of Interior of Earth

Here’s a diagram of the Earth’s interior layers:

Layers of Interior of Earth Layers

The three fundamental parts of the earth’s structure are the core, the mantle, and the crust. Only 15% of the Earth’s volume is made up of the core, and 84% is made up of the mantle. The crust represents the final 1% of the total.

Temperature, Pressure and Density of the Interior of Earth

Temperature.

• In mines and deep wells, the temperature rises with increasing depth. These findings, along with molten lava erupting from the earth’s interior, support the theory that the temperature rises towards the earth’s core.
• The various observations show that the rate of temperature increase is not uniform from the surface to the centre of the Earth. Initially, the rate of temperature increase is 1°C for every 32 metres of depth increase.
• The temperature rises at a rate of 120 degrees Celsius per kilometre in the upper 100 kilometres and 200 degrees Celsius per kilometre in the next 300 kilometres.
• However, as one descends deeper, this rate drops to just 100 C per km. As a result, it is assumed that the rate of temperature increase beneath the surface decreases towards the centre (do not confuse rate of temperature increase with temperature increase).
• The temperature is constantly rising from the earth’s surface to the centre. The temperature at the centre is estimated to be between 30000C and 50000C, but it could be much higher due to chemical reactions occurring under high-pressure conditions. Because of the heavy pressure of the overlying materials, the materials at the centre of the earth are solid even at such high temperatures.
• Pressure is increasing from the surface to the centre of the earth, just like temperature. This is due to the enormous weight of the overlying materials, such as rocks.
• It is estimated that the pressure in the deeper portions is nearly 3 to 4 million times greater than the pressure in the atmosphere at sea level.
• The materials beneath will melt towards the centre of the earth at high temperatures, but due to high pressure, these molten materials will acquire solid properties and are likely in a plastic state.
• The density of the earth’s layers increases towards the centre due to increased pressure and the presence of heavier materials such as nickel and iron.
• The average density of the layers rises from the crust to the core, reaching nearly 14.5g/cm 3 in the centre.

Interior of Earth UPSC

Only a few kilometres of the earth’s interior have we been able to directly witness through mining and drilling operations. Direct observations in the interior of the earth are mostly restricted by the quick rise in temperature below the surface of the planet. But even so, scientists have a good concept of what the interior of the earth looks like thanks to some direct and indirect sources.

This topic is of immense importance when it comes to UPSC Preparation. A candidate must be well-versed in Physical Geography. Notes for UPSC in addition to reading the UPSC Book and the NCERT Books for UPSC to cover this topic.

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Interior of Earth FAQs

What are the elements of earth's interior.

Iron, oxygen, silicon, and magnesium, are elements that may combine to form the crystalline Minerals known as silicates, make up more than 90% of the Earth's mass.

Why is the Earth's interior hot?

Radioactive element decay, residual heat from planetary formation, and heat produced as the liquid outer core solidifies close to its boundary with the inner core the main cause of heat in the Core.

What per cent of the Earth is the inner core?

Nearly 15% of the earth's volume and 32.5 percent of its mass are made up of the core.

Which is the cold layer of the earth?

The crust is the cold layer of the earth, the more we go deep in the earth the hotter it is.

Which is the hottest layer of Earth?

The core is the hottest layer of Earth.

Which mineral does crust contain?

Silica (Si) and Aluminium (Al) are the two main components of the crust, which is why it is Commonly referred to as SIAL.

Which mineral does the core contain?

The core is also called NIFE since it contains nickel (Ni) and iron (Fe).

What is the density of the mantle?

The density of the layer, which ranges from 3.3 to 5.4g/cm3, is greater than that of the crust.

Which mineral does the mantle contain?

Because it is primarily composed of silicon and magnesium, the mantle is also known as SIMA.

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• Interior Of Earth

Interior of the Earth

The crust, the mantle, and the core are the three layers that make up the earth. The core only forms 15 per cent of the Earth’s volume, whereas the mantle occupies 84 per cent. The remaining 1 per cent is made up of the crust.

From the picture, we see that at the centre of the Earth lies the core, then there is the mantle and finally the crust.

Understanding the Core, Mantle and Crust

The centre of the Earth is made of a dense metallic core. It is due to the metallic nature of the Earth’s core, a magnetic field is present on the planet. A lot has been understood about the features of the crust by documenting the travel time of the seismic wave generated by earthquakes through different layers of the Earth. The Earth’s core is composed of a solid inner core and a liquid outer core. We know this because S-waves stop at the inner core. The strong magnetic field is generated by convection in the liquid outer core.

There are two important things that we know about the mantle: 1) that it is made of solid rock 2) it is hot. Scientists know the structure of the mantle because of the heat flow, seismic waves and meteorites. Heat flows through the Earth in two ways: convection and conduction . Conduction is a heat transfer method that occurs only through rapid collisions of atoms. This can happen only when the material is solid. The nature of heat is to flow from warmer to cooler places until an equilibrium of temperature between the two medium is reached. The mantle is hot because of the heat conducted from the inner core of the earth.

The bottom layer of mantle material is heated by the heat emanated by the core, due to this the particles move rapidly, decreasing their density and causing them to rise. A convection current is originated due to the rising current. On reaching the surface, the warm material spreads horizontally. The material rapidly cools down because it is no longer near the proximity of the core. Eventually, it becomes cool and dense enough to sink back down into the mantle. At the bottom of the mantle, the material traverses horizontally and the core heats it up. It reaches the location where warm mantle material rises, and the mantle convection cell is complete.

The outer surface of the Earth is known as the crust and it is a cold, thin, brittle outer shell made of rock. There are two types of crust each with its own distinctive physical and chemical properties: a) Oceanic Crust b) Continental Crust.

The oceanic crust is made of magma that erupts on the surface of the seafloor to create basalt lava flows. It sinks deeper down and creates intrusive igneous rocks . Continental crust is composed of many types of metamorphic, igneous and sedimentary rocks.

Here is a video explanation of the interior of the Earth with animations!

Frequently Asked Questions on Interior of the Earth

Who studies the interior of earth.

The study of seismic waves is known as seismology. Seismologists use seismic waves to learn about earthquakes and also to learn about the Earth’s interior. One ingenious way scientists learn about Earth’s interior is by looking at earthquake waves.

What is the inside of Earth made of?

The Earth is made out of many things. Deep inside Earth, near its centre, lies Earth’s core which is mostly made up of nickel and iron. Above the core is Earth’s mantle, which is made up of rock containing silicon, iron, magnesium, aluminium, oxygen and other minerals.

What per cent of the Earth is the inner core?

The three main layers of Earth include the crust (1 per cent of Earth’s volume), the mantle (84 per cent), and the core (inner and outer combined, 15 per cent).

How do we know what Earth’s interior looks like?

Seismic waves from large earthquakes pass throughout the Earth. These waves contain vital information about the internal structure of the Earth. As seismic waves pass through the Earth, they are refracted or bent, like rays of light when they pass through a glass prism.

Which is the hottest layer of Earth?

The inner core is the hottest layer.

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Layers of The Earth

Earth is the fifth largest planet in our solar system, and the only one proven to support life. It has multiple layers, with each having distinct characteristic features. If we could slice the planet to half, we would see it is composed of multiple layers, arranged one above the other.

Why Does the Earth have Different Layers and How Are They Formed

According to a general conception, during its formation, the earth underwent a period of differentiation, with the heaviest elements sinking to the center and the lighter ones rising to the surface, thus causing the earth to develop layers as it cooled.The resulting chemical composition can define the earth’s internal layering. Scientists discovered the different layers of the earth based on the study of seismic waves that are generated by earthquakes and explosions that travel through the earth and across its surface. 

How Many Layers Does the Earth Have, and What Are They Called

The earth’s internal structure is made up of three major layers: the crust, the mantle, and the core, The mantle and the core are further subdivided to form five distinct layers in total. Each of the layers involving the main layers has its own set of characteristics that are described below along with their chemical compositions, and physical or mechanical properties. The names of these layers, in order of their presence from the top, are as follows:

2. Upper Mantle

3. lower mantle, 4. outer core, 5. inner core, all the earth’s layers, their structure and composition.

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

Density : ∼ 2830 kg/m 3 at the continental crust and ∼ 3000 kg/m 3 at the oceanic crust

It is the outermost and thinnest layer of our planet and is least dense among all other layers. Based on its thickness and location, the crust is of two types, the continental crust that consists of granite rocks and found near the mountain ranges, and the oceanic crust that consists of basalt and found under the oceans. The most abundant elements found in the earth’s crust include oxygen, silicon, aluminum, iron, and calcium. The temperature within the earth’s crust is high enough to melt rocks and form the lower layer called the 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)

Density : ∼ 3400 kg/m 3

It is the largest and thickest layer of earth. The upper mantle, along with the crust, makes up the lithosphere of earth, which is physically distinct from the layers lying below due to its low temperature high thickness. Below the lithosphere is found a much hotter and malleable portion of the upper mantle called the asthenosphere layer that begins at the bottom of the lithosphere and extends up to 450 miles (700 km) deep inside.The composition of the upper mantle is not found to be in a steady-state but always in constant motion. The upper mantle moves large areas of crust, called tectonic plates, resulting in the formation of volcanoes, mountains, or earthquakes. Between the upper and lower mantle, there is the presence of the transition zone, which ranges in depth from 250 – 410 miles (410 – 660 km).

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)

Density : ∼ 4400 kg/m 3

It is found below the upper mantle from a depth of about 400 miles (650 km) down to 1,800 miles (2,900 km) and is thus incredibly large and takes up most of the earth’s volume. Being so deep inside the earth, the temperature and pressure of the lower mantle are extremely high. Here in the lower mantle, the convection currents allow heat from the interior of the earth to rise to the surface. 

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/m 3

Found below the mantle and having a composition similar to the inner core with 80% iron, along with nickel and some other lighter elements. The outer core has a very high density and thus always found to exist in the viscous-liquid state due to not having enough pressure to be compressed to a solid. 

Temperature:  5,700 K (∼5,500°C)

Thickness:  760 miles (∼1,220 km)

Density : 12,600 – 13,000 kg/m 3

It is the center, and the hottest part of the earth. Similar to the outer core, the inner core is composed primarily of iron and nickel and has the highest density among all other layers. The inner core is made mostly metals such as gold, platinum, palladium, silver, and tungsten. Due to extremely high temperature and pressure, the metals present in the inner core change their structural conformation and are found to exist in solid state. Recent discoveries also suggest that the solid inner core itself is composed of two layers, separated by a transition zone of about 150 – 250 miles (250 – 400 km) thickness.

Ans. The lithosphere includes the brittle upper portion of the mantle, and the crust or outer layer of the earth’s surface.

Ans. The lithosphere is the mechanical layer of the earth that contains the seven major plates, which include the African, Antarctic, Eurasian, North American, South American, India-Australian, and the Pacific plates.

Ans. Asthenosphere is the earth’s only layer that is mechanically weak and thus can be easily deformed.

• What are the Earth’s layers? – Phys.org
• Explainer: Earth — layer by layer – Sciencenewsforstudents.org
• What are the layers of the Earth? – Zmescience.com
• The Composition and Structure of Earth – Courses.lumenlearning.com

Article was last reviewed on Thursday, February 2, 2023

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5 responses to “Layers of The Earth”

Can someone explain to me how did the scientists come up with the conclusion about the thickness of each layer without going there or exploring it?

By measuring the time of travel of refracted and reflected seismic waves, scientists could infer the thickness of each layer of Earth.

This is really helpful

Very informational and helpful! I would definitely recommend.

this helped me a lot thanks guys

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