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.
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).
INTERNAL AND EXTERNAL STRUCTURE OF THE EARTH){kind=link}
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