THE INTERNAL STRUCTURE OF THE EARTH

 The earth is a system which composed of two zones/parts. These are

1.  Inner zone (Internal Structure)

2.  Outer zone (External Structure)

Thus, the structure of the earth consists of external structure and internal structure.

 INTERNAL STRUCTURE / CONCENTRIC ZONE OF THE EARTH

The internal structure of the Earth refers to the arrangement of different layers found beneath the Earth’s surface. Scientists understand this structure mainly through the study of seismic waves produced by earthquakes, because the Earth’s interior cannot be observed directly. Internal structure of the earth sometimes called concentric zones of earth or interior parts of earth. It made by three layers which are Crust, mantle and core.  

The internal structure of the earth consists of three zones/layers which are classified based on the density of their rock. The less dense rocks float on top of the denser rocks the heavier elements, like iron and nickel, are most prevalent within the Earth’s core. These zones are

i) Lithosphere/crust

ii) Mesosphere/Mantle iii) Barysphere /Core. 

 

1. THE CRUST/ LITHOSPHERE

 

þ  Is the outermost and thinnest zone of the earth which found between 8 – 50km or 5 – 30 miles.

þ  It has an average density of 2.7g/cm3.

þ  It is largely composed of igneous rocks.

þ  Other types of rocks also exist as a result of changes on the earth’s surface. When subjected to forces or any stress.

þ  The crust also consists of two sub-layers, sial and sima.

 

a). THE SIAL LAYER

• Is the outer layer or the continental part of the crust which is composed of different types of rocks. These rocks are mainly rich in Silica and Aluminium minerals
• The sial for the basis of the continent.
• The presence of silica and aluminium minerals collectively form SIAL layer.

 

b). THE SIMA

• Is the layer which found beneath the sial.
• Is the inner layer of the crust which separated from sial layer by the zone called Conrad discontinuity line.
• The sima layer is composed by silica and magnesium.
• It forms the basis of  the ocean floor.

 

Note: - Sial and sima layer together forms the crust. The sial layer consist of granites rocks with density of about 2.65g/cm3

The presence of silica and aluminium minerals collectively form SIAL layer.

                       NOTE: - Sial and sima layer together forms the crust.

🌱 Easy explanation

Think of the Earth like a layered cake 🎂:

• The top soft layer is called SIAL
  👉 It is where we live (land, mountains, houses)
  👉 It is lighter, like a sponge
• The layer below is called SIMA
  👉 It is heavier and stronger
  👉 It is mostly under the oceans

🧠 Simple way to remember

• SIAL = land (light layer)
• SIMA = ocean (heavy layer)

 

GENERAL CHARACTERISTICS OF THE CRUST 

1.       The crust is the outermost and first layer of the Earth forming the continents and the ocean floor 

2.       Size / Thickness of the crust is 8 to 50km. 

3.       The average density of crust is 2.7 gram per cubic cm 

4.       It is mainly composed of silica and aluminum in the continental crust and silica and magnesium in the oceanic crust 

5.       The temperature of the crust is low at the surface and increases gradually with depth. 

2. THE MANTLE/ MESOSPHERE

 

Mesosphere or mantle is found between the crust and core.

•       It is made up of very dense igneous rocks rich mostly in iron, silicon, oxygen, aluminium, and magnesium.

•       The mantle extends from 51 km to 2900 km into the earth.

•       It separated from the crust by the zone of separation called Mohorovic discontinuity line.

•       It consists of rocks with a density of 3.03g/cm3 – 3.4g/cm3

•       It consists of pale green minerals called Olivine (Ferromagnesium silicate) in form of ultra-basic rock

•       Mantle is divided into two parts, the lower mantle and upper mantle.

•       The upper mantle is rigid/solid and it combines with the crust to form a large layer called lithosphere.

•       The lower mantle is less rigid and forms the molten layer within the earth’s interior called asthenosphere

 Asthenosphere is the molten layer which responsible for the balancing movement of the earth’s material called isostatic readjustment.

HINT:

 The boundary between the crust and the next layer down, the upper mantle, is called the Moho (named after the man who discovered it). It's the final stop before you enter the Earth's fiery hot kitchen!

-     Asthenosphere has been investigated is found between 100 to 200km below the upper surface. 

 

GENERAL CHARACTERISTICS OF THE MANTLE 

1.     The density of the mantle ranges from about 3.3 g/cm³ to 3.4 g/cm³, especially in the upper mantle 

2.     The temperature in the mantle is very high and may reach up to 3,500°C 

3.     It is mainly composed of iron, silicon, magnesium, and aluminum  

4.     The mantle is much thicker than the crust, extending to a depth of about 2,900 km 

5.     It is divided into the upper mantle, which is mostly solid, and the lower mantle, which behaves in a more plastic or semi-molten manner 

3. THE CORE/ BARYSPHERE

 

•       The core is the innermost zone/layer of the internal structure of the earth.

•       It composed mainly by iron and nickel minerals

•       It is under tremendous pressure and heat, with the average density of about 10.5g/cm3

 The core is also classified into two parts, the outer and inner core;

             

 

             The outer core:

 

•       The outer core is about 2300 km thick, and it comprises very hot molten rock materials composed of nickel and iron

•       The movement of these molten materials generates powerful electric currents, which, in turn, creates the Earth’s magnetic field. The magnetic field is essential for life on earth as it protect the planet harmful solar radiation and charged particles from the sun.

•       The temperature and density constantly increase along the border between the mantle and the core, making the outer core liquid-like, with the temperature about 3700 C along the border. 

 

The inner core:

 

•       The inner core is solid in nature because of high pressure exerted from different parts toward the center. It has a temperature of about 5500 C and density of about 16-17g/cm3

•       The inner core has a diameter of about 2600 – 2700km. (1600 – 1700 miles).

 

 The core is separated from the mantle by zone of separation called Gutenberg discontinuity.

 

GENERAL CHARACTERISTICS OF THE CORE 

 

1. It is the innermost layer of the Earth 2. It is divided into outer core (liquid) and inner core (solid)  

3.     It is mainly composed of iron and nickel (NiFe) 

4.     Temperatures can reach up to about 5,500°C 

5.     It has a thickness of about 3,480 km 

6.     The density is very high, about 10.5 g/cm³ 

7.     It is responsible for the Earth’s magnetic field