Layers of the Earth: Inner and Outer Core, Mantle and Crust

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Namrata Das

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Earth consists of four separate layers. This is part of Earth that we can only see superficially. If you end up grabbing earth and cutting it in the middle, you will see different layers. The inside of reality still holds back quite a few secrets from us. Similar to all other terrestrial planets, the interior of the earth is also differentiated. Here, we will study the layers of the Earth in detail along with some important questions.

The layers of earth can be compared to that of an onion skin. If you peel it, you notice that it is different from each other. Most of the geologists, after years of research, firmly believe that as the Earth cooled, the heavier and the denser material sank into the center and the lighter ones rose towards the top. As a result, the outermost layer is composed of the lightest elements, such as rocks and granites, while the innermost layer is composed of nickel and iron.

Different Layers of Earth

According to most of the geologists, as the Earth cooled, the heavier and the denser material sank into the centre, and the lighter ones rose towards the top. This is the reason why the outermost layer is made of the lightest materials such as rocks and granites while the innermost layer comprises nickel and iron. Earth consists of four separate layers, which are: the inner core, the outer core, mantle, and crust make up the four layers of earth.

The Inner Core

It is at the center and by far the hottest layer on earth. This inner core consists of solid and is made up of iron and nickel, having a temperature of 5,550 degrees Celsius. It acts as the engine room for mother earth. The major reason why iron and other heavy metals can withstand such high temperatures is that their liquefying temperatures rise dramatically at the weights present, which range from about 330 to 360 gigapascals. Because the inner core isn't inextricably linked to the Earth's strong mantle, the possibility that it rotates faster or slower than the rest of the planet has long been discussed. Researchers estimate that the inner core pivots at a pace of one degree faster than the surface based on variations in seismic waves as they pass through the core over decades. Later geophysical evaluations estimate the rate of rotation to be between 0.3 and 0.5 degrees per year in relation to the surface.

According to recent discoveries, the solid inner core is made up of layers separated by a shifting zone that is between 250 and 400 kilometers thick. The deepest layer of the core, which contains an inner core, is estimated to be 1,180 km (733 miles) wide in this fresh viewpoint on the inner core, making it not precisely a big percentage of the inner core's measurement. It's also been suggested that, while the core is comprised of iron, whatever remains of the inner core might be in a different crystalline structure.

Furthermore, further investigations have led geologists to believe that the deep within elements are causing the Earth's inner core to grow at a pace of about 1 mm each year. This occurs because the inner core is unable to break down the indistinguishable amount of light components from the outer core.

The Outer Core

This can be compared to a very hot ball of metals. The temperature ranges from 4000-degree Fahrenheit to 9000-degree Fahrenheit. It is exceptional which is why it is all in the liquid state. The outer core is placed at 1800 miles below the crust and is about 1400 miles thick. It is formed of metals like iron and nickel.. The outer core does surround the inner core.

The inner core's pressures and temperatures are so high that the metals are pushed together and unable to flow freely like a liquid, forcing them to vibrate rather than solidify.

Mantle

The Earth's mantle is the widest part of the planet. It has a thickness of 2,900 kilometers. The majority of the mantle is made up of magma, a semi-molten rock. The rock in the top portion of the mantle is hard, but it becomes softer and melts as it descends.

The mantle lies just beneath the Sima. The mantle is made up of extremely hot and thick rock. Under tremendous weight, this layer of rock flows like asphalt. The largest temperature variations from the bottom to the top of the mantle create this flow. The movement of the Earth's plates is caused by the movement of the mantle. Its temperature varies from 1600°F near the top to 4000°F near the bottom.

Crust

The crust is the outermost layer of the Earth's surface, where we dwell. The thickness is between 0 to 60 kilometers. It's a solid rock layer that comes in two types:

  • The continental crust covers the land
  •  the oceanic crust covers the sea.

The crust has been researched and understood the most. The mantle is very hot and can flow. If we can get to the heart of the Earth, we can be squashed into a ball smaller than a marble since the outside and inner cores are considerably hotter with great pressures.

History of the Study

We have always wanted to understand the earth’s composition and formation. Most of the earliest known facts were mostly unscientific in nature. In other words, it has been borrowed from myths and religious stories that mostly involved a supernatural force.

During the period of medieval earth, a lot of theories came up regarding the Earth’s origin and its composition. Most of the theories revolved around the earth being flat.

In the 6th century, it was discussed and speculated as to how the earth is ideally round and then spherical. During this period, a theory of earth made rounds wherein it was made up of minerals and metals. Only by the 17th century, did we start understanding earth’s structure.

Finally, in the 19th century, it was confirmed that the earth’s liquid core is a solid inner core. By the end of the 20th century, a theory was established about Earth and its dynamics & structure.

To have a proper understanding of the topic, refer to this video:

Things to Remember

  • The very center of the Earth is the core which is mostly iron and nickel. 
  • The inner core is the solid which measures 1, 516 miles in diameter.
  • The outer core of the Earth is a liquid metal which is also mostly nickel and iron. 
  • The outer core is 1,408 miles in diameter.
  • The mantle of the Earth is solid rock, however, it is not completely hard. 
  • The mantle moves slowly and this movement causes earthquakes and volcanic eruptions. 

Sample Questions

Ques: Mention the three major layers of the interior of the Earth. (1 mark)

Ans: The three major layers of the interior of the Earth are the core, the mantle and the crust. 

Ques: This is the solid outer part of the Earth: (1 mark)

  • Lithosphere 
  • Atmosphere 
  • Hydrosphere 
  • Biosphere 

Ans: The correct answer is a. Lithosphere.

Ques: The ______ is the rigid outer layer of the Earth. (1 mark)

  1. Crust 
  2. Mantle 
  3. Core 
  4. Inner core

Ans: a. Crust is the rigid outer layer of the Earth. 

Ques: ______ layer is made up of liquid iron. (1 mark)

  1. Mantle 
  2. Crust 
  3. Outer core 
  4. Inner core

Ans: Outer core layer is made up of liquid iron.

Ques: Differentiate between crust and core of the Eart. (3 marks)

Ans: 

Crust 

Core 

This is the outermost layer of the Earth.

This is the innermost layer of the Earth. 

The crust has an average density of 2.73.

Core has a density of 17.2.

The crust covers about 0.5% by part of the Earth.

It covers about 83% by part of the Earth.

Ques: What are the different layers of the Earth? (2 marks)

Ans: According to most of the geologists, as the Earth cooled, the heavier and the denser material sank into the centre, and the lighter ones rose towards the top. This is the reason why the outermost layer is made of the lightest materials such as rocks and granites while the innermost layer comprises nickel and iron. Earth consists of four separate layers, which are: the inner core, the outer core, mantle, and crust make up the four layers of earth.

Ques: What are the inner and outer cores of the Earth? (3 marks)

Ans: Inner core: It is at the center and by far the hottest layer on earth. This inner core consists of solid and is made up of iron and nickel, having a temperature of 5,550 degrees Celsius. It acts as the engine room for mother earth. 

Outer core: This can be compared to a very hot ball of metals. The temperature ranges from 4000-degree Fahrenheit to 9000-degree Fahrenheit. It is exceptional which is why it is all in the liquid state. The outer core is placed at 1800 miles below the crust and is about 1400 miles thick. It is formed of metals like iron and nickel. The outer core does surround the inner core.

Ques: What is meant by mantle? (2 marks)

Ans: The Earth's mantle is the widest part of the planet. It has a thickness of 2,900 kilometers. The majority of the mantle is made up of magma, a semi-molten rock. The rock in the top portion of the mantle is hard, but it becomes softer and melts as it descends.

Ques: What is the crust? (2 marks)

Ans: The crust is the outermost layer of the Earth's surface, where we dwell. The thickness is between 0 to 60 kilometers. It's a solid rock layer that comes in two types:

  • The continental crust covers the land
  •  the oceanic crust covers the sea.

Ques: Consider the various sources of information that are connected to the Earth’s interior. Classify the above as DIRECT or INDIRECT sources of information. Give reasons. (3 marks)

Ans: The various sources of information that are connected to the Earth’s interior are:

  • Seismic activity: Frequency and size of an earthquake. 
  • Earth’s magnetism: Because of the movement of the molten material under the earth’s curst. 
  • Volcanoes: A rupture in the crust of the Earth that allows hot lava, volcanic ash, and gases to escape. 
  • Mined rocks: Excavating hard minerals. 
  • Gravitational force: A natural phenomenon. 
  • Meteors: A bright streak of light.

Ques: Describe a few characteristic features of the mantle. (3 marks)

Ans: The characteristic features of the mantle are as follows:

  1. The mantle extends from Moho’s discontinuity to a depth of around 2, 900 km. the upper portion of the mantle is known as the aesthenosphere. 
  2. The mantle is the main source of magma that forms its way to the surface during volcanic eruptions. It has a density higher than that of the crust.
  3. The crust and the uppermost mantle together form the lithosphere. Its thickness ranges from 10-200 km. the lower mantle extends beyond the aesthenosphere.

CBSE X Related Questions

1.
Explain the following in terms of gain or loss of oxygen with two examples each. 
(a) Oxidation
(b) Reduction

      2.

      A milkman adds a very small amount of baking soda to fresh milk.
      (a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline?
      (b) Why does this milk take a long time to set as curd?

          3.
          Light enters from air to glass having refractive index 1.50. What is the speed of light in the glass? The speed of light in vacuum is 3 × 108 m s−1.

              4.
              Balance the following chemical equations.
              (a) HNO3 +Ca(OH)2 \(→\) Ca(NO3)2 + H2
              (b) NaOH + H2SO4 \(→\) Na2SO4 + H2
              (c) NaCl + AgNO3 \(→\) AgCl + NaNO3 
              (d) BaCl + H2 SO4 \(→\) BaSO4 + HCl

                  5.
                  Oil and fat containing food items are flushed with nitrogen. Why?

                      6.

                      What are the differences between aerobic and anaerobic respiration? Name some organisms that use the anaerobic mode of respiration.

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