(R.SQUARE)INTERNAL AND EXTERNAL STRUCTURE OF THE EARTH

At the beginning of creation, the earth was a heated gaspind. This gaspind gradually cools and condenses. The lining that falls on it at this time is the crust. There are three layers of underground. Ashmandala, Gurumandala and Kendramandala. The common name of the material made of earth is rock. The various landforms that operate on Earth are affected by the type of rocks and minerals. The surface is always changing. This change is twofold. Slow change and sudden change. In this chapter we will discuss the internal and external structure of the earth, different types of rocks, slow and sudden changes in the earth's surface and different topography.

The Earth is made up of 4 different layers.  They each have unique characteristics as described below.

Structure of the Earth

Crust

The crust is the thinnest layer of the earth and it is the layer where we live. It is made up of different types of rocks and can be up to 70 km thick in different places. The crust itself is divided into large parts called tectonic plates. There are about 7 large plates and 12 small plates, which “float” in the mantle beneath them. The plates themselves are made up of 2 different types of crust, the continental crust under the earth and the crust under the sea. The continental crust is dense (25-70 km) and light because it is composed of low-density rocks. The oceanic crust is thin (6-11 km) and heavier because it is composed of rocks (mainly igneous rocks) that have a higher density. The oceanic crust covers 2/3 of the Earth's surface.

Outer Core

The outer core is made of liquid iron and nickel and is in the range of 3,500-4,000°C.  as the liquid metal rotates, it induces a current that creates the earth's magnetic field. The heat from the core feeds the currents of convection to the mantle. It is 2,900 km thick.

Inner Core

The warmest part of the world: The inner core is the warmest part of the earth, reaching temperatures between 4,000-4,700 degrees Celsius, which is as hot as the surface of the sun. It is made of hard iron and nickel which are under so much pressure that they cannot melt. It produces intense heat as 1,200 km thick and heavy radioactive material decays.

Mantle

The mantle is the thickest layer of the Earth at 2,900km thick.  It makes up nearly 80% of the volume of the Earth.  The mantle itself is divided into 2 layers, the upper and lower mantles and the heat within these layers 

Internal Structure of the Earth    

At the time of creation, the earth was a heated gaspind. From the heated state it cools and condenses. During this time heavy matter from outside the earth accumulates towards its center. And the light elements are deposited in layers from bottom to top according to the difference in mass. These different layers of the earth are called zones. The upper layer is called the fossa. The upper part of the equator is known as the crust.

Rocks on the ground are that hard. The crust is visible so the crust. The thickness of the crust is the lowest compared to other layers of the interior; 20 km on average. The crust averages 35 km at the bottom of the continent and only 5 km thick at the bottom of the ocean. This layer of the continental crust is generally called the Sial layer, which is made up of silicon (Si) and aluminum (AI), which is heavier than the Sial layer, and its main minerals are Silicon (Si) and Magnesium (Mg), commonly called Sima. It is estimated that this basalt layer exists all over the world in the outer and deep-sea floor. Appearance can be seen in the upper part of the crust. Such as- mountains, plateaus, plains etc. At the bottom of the ghost, the temperature rises by 30 degrees Celsius per kilometer.

Barysphere

Purumandal is called Gurumandal up to 2.885 km below the crust. The mantle is composed mainly of basalt rock. This part contains silica, magnesium, iron, carbon and other minerals.

Gurmandal is divided into two parts.

(A) Upper Gurumandal which extends up to 700 km. This zone is mainly composed of silicate minerals rich in iron and magnesium.

(B) LOWER Gurumandala is mainly composed of minerals rich in iron oxide, magnesium oxide and silicon dioxide.

 

Centrosphere

Kendramandal is right after Gurumandal. This zone extends from the bottom of the Gurumandal to the center of the earth. This layer is about 3,486 km thick. With the help of seismic waves, it is known that the center has a liquid outer layer, which is about 2,270 km thick, and a solid inner layer, which is 1,216 km thick. Scientists believe that the elements in the nucleus include lead, nickel, mercury, and lead. However, the main ingredients are nickel and lead. 

 

EXTERNAL STRUCTURE OF THE EARTH

The Main Landforms of the Earth

The surface is not the same everywhere. There are several differences in its shape, nature and structure. This shape and structural feature of the land is called landform. Somewhere on the surface there are high mountains, somewhere plains, somewhere mountains, somewhere plateaus. There are also differences in height, friendliness and slope in

different places. Judging from the geographical aspect, the entire topography of the earth can be divided into three parts.

These are-

(1) mountain,

(2) Plateau,

(3) Plains.

Mountains

Mountains are elaborate and steeply sloping rock formations at least 1,000 meters above sea level. A low-lying rock mass, usually 600 to 1,000 meters high, is called a mountain. The height of the mountain can be a few thousand meters above sea level. The topography of the mountain is friendly, the slope is very steep and usually peaks. Some mountains are isolated- For example, Kilimanjaro in East Africa. Some mountains cover a wide area with many separate peaks. For example, the Himalayas.

Classification of mountains. There are four main types of mountains based on their origin and structure. E.g.

(A) Fold Mountains

(B) Volcanic Mountains

(C) Fault-block mountains

(D)Dome /Laccolith Mountains.

Plateaus

A plateau is a vast plain that is steeply sloping from the mountains but steep from the plains. The height of the plateau can range from a hundred meters to a few thousand meters. The world's largest plateau is 4,270 to 5,190 meters high.

There are three types of plateaus based on location. E.g.

1.Intermontane Plateau

2.Piedmont Plateau

3.Continental Plateau

Plains

A plain is a vast expanse of land with a gentle slope a little above sea level. Plains are formed as a result of erosion and accumulation of various geological processes such as rivers, glaciers and winds. The plains are very suitable for agriculture, living, road construction due to the gentle slope and low friendliness. So, the densest settlements have developed in the plains.

The plains can be divided into two main parts based on the type of origin -e.g.

1.Erosional plains and

2.Depositional plains.

Erosional plains

Erosion of various natural forces such as river flows, wind currents and glaciers cause the erosion of a plateau and the formation of eroded plains. The Appalachian foothills, Finland and Siberia in Europe are such eroded plains.

The Chattar of Madhupur and Barindro lands in Bangladesh are two examples of eroded plains.

Depositional plains.

Sedimentary plains are formed by the accumulation of silt, sand and dust in a low-lying area by natural forces like rivers, glaciers, wind currents etc. Such accumulated plains can occur in any location, from the highlands to the coast. For example, the pravan plain formed by sedimentation of the river, the delta formed by the accumulation of rivers near the mouth of the river, the glacier plain formed by the silt accumulated by the glacier line in the temperate zone.

AUTHOR -M.ZAMAN(RASEL).