The Interior of The Earth: Earth interior – Crust, Mental and Core, Diagam, Explanation

The Interior of The Earth

The interior of the earth can be understood only by indirect evidence as no one has reached the interior of the earth.

The landscape is continuously shaped by Exogenic and endogenic processes. These processes help to understand the physiographic character of the earth.

To understand why the earth shakes or how a tsunami wave is generated, it is necessary that we know certain details of the earth’s interior.

You can also check – Geography Notes For UPSC

Source of Information About the Earth’s Interior

The earth’s radius is 6,370 km. No one can reach the centre of the earth and make observations or collect samples of the material. scientists tell us about the earth’s interior and the type of materials that exist at such depths based on estimates and inferences.

Direct Source

• Surface rock: Surface rock is readily available at the surface of the earth. By observing these rocks, we can know the form of material that can be found up to a certain depth.
• Volcanos:  Volcanic material that gets out after an eruption is readily available to us for observation. Since these materials come up from great depth, therefore, the quality of this material at great depth can be analyzed directly. However, the accurate depth of material can’t be ascertained.
• Mining and Drilling Projects: From Mining and Drilling areas, many materials can be sourced for analysis. These materials reveal the nature of material available at a certain depth. From mining, it is easy to deduce that pressure and temperature increase from the surface towards the interior deeper depth. Also, the Density of the material increases from the top surface to the interior bottom.
  • Through the mining activity, we get information that temperature and pressure increase with the increasing distance from the surface towards the interior of the earth in deeper depths.
  • it is also known that the density of the material also increases with depth.
• Deep Ocean Drilling Project: Two major projects are the “Deep Ocean Drilling Project” and the “Integrated Ocean Drilling Project”.
• Integrated Ocean Drilling Project: The deepest drill at Kola, in the Arctic Ocean, has so far reached a depth of 12 km. This and many deep drilling projects have provided a large volume of information through the analysis of materials collected at different depths.

Indirect Sources

Since the Direct source materials can be accessed up to a certain depth. Beyond that depth, it is not possible to know the quality of interior of the earth. To overcome this, Scientists use technologies like the application of gravitation, magnetic and seismic knowledge to know the interior of the earth. Further, scientists also consider meteorites as an indirect source because, once, it was part of a planet.

• Temperature and pressure variation
• Seismic activities: It provides information what’s the state of the interior of the earth. Whether it’s solid, liquid, or in gaseous form. The technology revealed that the mantle is liquid, the outer core is liquid but the inner core is solid.
• Meteorites: Meteorites are found in space and seldom reach the earth. When it reaches the earth, It is available for analysis. Meteorites are not from the interior of the earth; therefore, it has an indirect source to acquire the interior of the earth because scientists assume that Meteorites were once part of the planet, therefore, their structure and material is similar to the earth.
• Gravitation: Gravitational value is not the same across all the latitudes. The differences in gravitational value ( gravitational anomaly ) show the uneven distribution of mass of material within the earth.
• Magnetic field: Magnetic survey in crust reveals the distribution of magnetic materials available in crust.

To understand this you have to study earthquakes and earthquake waves.

Internal Structure of Earth

The Crust

It is the outermost solid part of the earth. It is brittle in nature. The thickness of the crust varies under the oceanic and continental areas. The oceanic crust is thinner as compared to the continental crust.

• The mean thickness of the oceanic crust is 5 km whereas that of the continental is around 30 km.
• The continental crust is thicker in the areas of major mountain systems. It is as much as 70 km thick in the Himalayan region.
• It is made up of heavier rocks having a density of 3 g/cm3.
• This type of rock found in the oceanic crust is basalt.
• The mean density of material in oceanic crust is 2.7 g/cm3.
• The temperature of the crust rises with depth, reaching levels of around 200°C to 400°C near the mantle-crust boundary.
  • In the higher region of the crust, the temperature rises by up to 30 degrees Celsius for every kilometer.
• The lighter silicates — silica + aluminum (also known as sial ) — make up the continents, while the heavier silicates — silica + magnesium (also known as sima) — make up the oceans [Suess,1831–1914, this categorization is now obsolete (out of date)].

The most abundant elements of the Earth’s Crust

Lithosphere

• The lithosphere is the earth’s rigid outer layer, with a thickness ranging from 10 to 200 kilometers.
• It consists of the crust as well as the upper part of the mantle.

The Mantle:

The portion of the interior beyond the crust is called the mantle.

• The mantle extends from Moho’s discontinuity to a depth of 2,900 km.
• The upper portion of the mantle is called the asthenosphere.
  • The word astheno means weak.
  • It is considered to be extending up to 400 km. It is the main source of magma that finds its way to the surface during volcanic eruptions.
  • It has a density higher than the crust’s (3.4 g/cm3).
• The lower mantle extends beyond the asthenosphere. It is in a solid state.
• The density of mantle is higher than the crust and varies from 3.3 to 5.5.
  • The upper mantle’s density ranges from 2.9 to 3.3 grams per cubic meter.
  • In the lower mantle, density ranges from 3.3 g/cm3 to 5.7 g/cm3.
• The mantle has been formed largely of silicate minerals rich in iron and magnesium.
• The mantle is made up of 45% oxygen, 21% silicon, and 23% magnesium (OSM).
• Temperatures in the mantle range from around 200 °C at the upper crustal border to almost 4,000 °C at the core-mantle boundary.

The Core

• The core-mantle boundary is located at a depth of 2,900 km to 6378 km.
• The density of material at the mantle core boundary is around 5 g/cm3 and at the centre of the earth at 6,300 km, the density value is around 13g/cm3.
• The core is made up of very heavy material mostly constituted by nickel and iron.
  • It is referred to as the nife layer.
• The core (inner core and outer core) makes up only around 16% of the earth’s volume but accounts for 33% of its mass.
• The outer core surrounds the inner core and is located between 2900 and 5100 kilometers beneath the surface of the earth.

Earth’s Layers- Seismic Discontinuities

Discontinuity refers to a sharp boundary between layers in the earth’s internal structure. Across these boundaries, seismic waves undergo significant changes in terms of their direction and speed.

• Conorod Discontinuity– between upper and lower crust
• Mohorovicic Discontinuity (Moho) – separates the crust from the asthenosphere (upper mantle), where there is a discontinuity in the seismic velocity. its average depth is about 35 km.
  • The cause of the Moho is thought to be a change in rock composition from rocks containing feldspar (above) to rocks that contain no feldspars (below).
• Repiti Discontinuity – between the upper and lower mantle
• Gutenberg Discontinuity – The core-mantle boundary is located at a depth of 2900 km is called the Gutenberg discontinuity, there is a sudden change from 5.5 gm/cm3 of the mantle to 10 gm/cm3.
• Lehman Discontinuity- between inner and outer core.

Earth’s Chemical Composition

Earth’s mass is approximately 5.97×10 kg (5,970 Yg).

Some Important Facts About the Interior of Earth

• The earth’s radius is 6,370 km.
• temperature and pressure increase with the increasing distance from the surface towards the interior of the earth
• the density of the material also increases with the depth.