Geography Project-I: Name - Pranay Sadani Class - 9 Sec - L

GEOGRAPHY PROJECT-I
NAME – PRANAY SADANI

CLASS – 9 SEC - L
ROLL NO. – B365/12
TOPIC – STRUCTURE OF THE EARTH
INTRODUCTION
Our planet Earth is more than 5,000 million years old and is still in the process of
changing.
In one year the Atlantic Ocean widens by 10 cm while the Pacific Ocean is
shrinking as the continents move slowly across the globe.
The Red Sea is in 'its infancy'. In 60 million years time it will be as wide as the
Atlantic Ocean. Africa and Asia may split apart as a result of the Mediterranean
merging with the Atlantic Ocean.
Layers of the Earth
The Earth comprises three main realms or regions- the Lithosphere which is the
solid, inorganic section, the Hydrosphere which is the liquid section and finally
the Atmosphere or gaseous section.
The thin outermost layer, the Earth's crust, averages about 17 km in thickness
throughout and is referred to as the mineral skin. It is made up of the continents
and oceans and from it emanates the soil, sediment salt, gases, liquid and all
components of the Earth in its widest connotation. The crust consists main of two
types of rocks-granite and basalt.
The composite zone inhabited by most living creatures is called Biosphere. It
includes a part of the atmosphere, the hydrosphere and a part of the lithosphere.
All three layers are essential for life to exist.
The Earth is primarily made of rocks, metals and water. Its surface is solid but its
interior is composed of molten matter due to the intense heat it experiences.
The temperature within the Earth increases with depth at the rate of 1°C for every
32 m depth, giving an average temperature of 5000°C at the centre of the Earth.
In spite of its molten interior, the Earth is firm and solid due to the great pressure
of the lithosphere. An idea of the interior structure of the Earth has been obtained
from a study of earthquake waves.
The Earth consists of three major concentric layers. These are called the Crust,
the Mantle and the Core of the Earth .The density, temperature and pressure of
these layers increase with depth.The chemical composition and physical state of
matter inside the Earth is of great concern for the study of landforms on the
surface of the Earth.
CROSS SECTION OF THE EARTH
CRUST
The word 'Lithosphere' means 'rocksphere' and is derived from the Latin
word 'Lithos' meaning 'rocks' or 'stones'. The Earth's crust averaging about
17 km thick, the mineral skin as it is referred to, is the most significant part
of the Earth's surface. The crust of the Earth is composed of a great variety
of igneous, metamorphic, and sedimentary rocks. The crust is underlain by
the mantle.
The crust is subdivided into two distinct parts according to its composition :-
1. 1.SIAL: The topmost layer consists of granitic rocks which on an
average, forms the first 25 km of the crust and is lighter, having an
average density of 2.7. gm/cm. This layer consists. of silicates and
aluminium and other lighter metals. This layer is called the Sial
(Sisilicate: Al-aluminium). The Sial layer is thick over the continents
but is thin or absent on the ocean. floors. (Fig. 4.2) especially the
Pacific Ocean.
2. SIMA: Below the Sial layer is a denser layer on an average 35 km
which consists predominantly of silicates of magnesium, iron and
other denser metals. It is a continuous zone of basaltic rocks forming
the ocean floors. This is called the Sima (Si-silicate; Ma-magnesium)
layer. The Sima layer has an average density of about 3.0 gm/ cm³.
Though these two layers are in a solid state, the lighter Sial is considered
as 'floating on the denser Sima layer. This arrangement of Sial floating on
Sima forms the basis of Wegner's 'Continental Drift Theory' and the super
continent Pangaea.
The composition of the crustal layer is of great interest because we get
most of our minerals from the Crust of the Earth. It also has the valuable
soil layer which is essential for the growth of both cultivated and wild plants.
The physical features of the Earth's crust influence land use and other
human activities. The density of human population also depends on the
nature of the relief features in an area.
CRUST OF THE EARTH
MANTLE
The boundary between the crust and the Mantle is called the Moho or Mohorovicic
Discontinuity density of 3.3 gm/cm³ and the density between this and the Gutenberg
Discontinuity (boundary between the mantle and the core) is 3.7 gm/cm³. The Moho or
the Mohorovicic Layer was named after the Yugoslav scientist, Andriya Mohorovicic
who discovered it. The Gutenberg Discontinuity was named after the German
seismologist named Beno Gutenberg.
The Mantle of the Earth lies below the crust of the Earth. The Mantle has an average
thickness of about 2,840 km. It consists of mixed silicates and metals (magnesium
and iron) and is rich in olivine .The density of the Mantle itself varies between 3.0
gm/cm³ and 5.5 gm/cm³.
Majorly, it has two subdivisions:-
1. The Upper Mantle or Asthenosphere is in a partially molten state. The velocity
of the earthquake waves decreases in it and hence it is referred to as the lower
velocity zones'. Though the temperature of this layer is quite high the average
temperature in this layer ranges between 850°C in the upper region and 2208°C
in the lowest region. However, the hot rocks rising from the interior of the Earth
often melt in the lowest depths forming molten magma. The high pressure of the
overlying layers keeps this layer in a solid state.
2. The Lower Mantle or Mesosphere . The lower mantle extends from about 660
kilometers (410 miles) to about 2,700 kilometers (1,678 miles) beneath Earth’s
surface. The lower mantle is hotter and denser than the upper mantle and
transition zone.The lower mantle is much less ductile than the upper mantle and
transition zone. Although heat usually corresponds to softening rocks, intense
pressure keeps the lower mantle solid. Geologists do not agree about the
structure of the lower mantle. Some geologists think that subducted slabs of
lithosphere have settled there. Other geologists think that the lower mantle is
entirely unmoving and does not even transfer heat by convection.
Mantle has two other divisions as well , namely – Transition Zone & D Double Prime
Earth's mantle plays an important role in the evolution of the crust and provides the
thermal and mechanical driving forces for plate tectonics. Heat liberated by the core is
transferred into the mantle where most of it (>90%) is convected through the mantle to
the base of the lithosphere.
The transfer of heat and material in the mantle helps determine the landscape of
Earth. Activity in the mantle drives plate tectonics, contributing to volcanoes, seafloor
spreading, earthquakes, and orogeny (mountain-building).
MANTLE – UPPER & LOWER
MANTLE
CORE
The density of the core is 13.0 g/cm³ in the centre It is a compound of alloys of carbon,
iron or silicon Due to the high temperature nickel and iron are found in molten stage.
The liquid iron generates its own electricity, and so under pressure, the core is the
source of the Earth's magnetic field.
According to some scientists, at the centre of the Earth there is a nucleus of high
density atoms that descended from the atoms that were the beginning of our Solar
System.
The Core of the Earth has a radius of about 3,500 km. It consists mostly of metals. As
nickel and iron are the two most abundant metals, the core is called Nife (Ni-nickel;
Feiron). The density of the core is between 13 g/cm³ to 15 g/cm³. This dense layer is also
called the Barysphere. The core of the Earth is estimated to have a temperature of about
5,000°C. The metallic core and the abundance of iron also explains the Earth's
magnetism. Usually the core is divided into inner and outer core. The outer core behaves
like liquid and does not allow earthquake waves to pass through it.
Subdivisions :-
• Outer Core – The outer core, about 2,200 kilometers (1,367 miles) thick, is
mostly composed of liquid iron and nickel. The NiFe alloy of the outer core is very
hot, between 4,500° and 5,500° Celsius (8,132° and 9,932° Fahrenheit). The
liquid metal of the outer core has very low viscosity, meaning it is easily deformed
and malleable. It is the site of violent convection. The churning metal of the outer
core creates and sustains Earth’s magnetic field.The hottest part of the core is
actually the Bullen discontinuity, where temperatures reach 6,000° Celsius
(10,800° Fahrenheit)—as hot as the surface of the sun.
• Inner Core – The inner core is a hot, dense ball of (mostly) iron. It has a radius of
about 1,220 kilometers (758 miles). Temperature in the inner core is about
5,200° Celsius (9,392° Fahrenheit). The pressure is nearly 3.6 million
atmosphere (atm).The temperature of the inner core is far above the melting
point of iron. However, unlike the outer core, the inner core is not liquid or even
molten. The inner core’s intense pressure—the entire rest of the planet and its
atmosphere—prevents the iron from melting. The pressure and density are
simply too great for the iron atoms to move into a liquid state. It rotates eastward,
like the surface, but it’s a little faster, making an extra rotation about every 1,000
years.
Earth's core is important for three main reasons: (1) it is responsible for the generation
of Earth's magnetic field; (2) it contains information regarding the earliest history of
accretion of the planet; and (3) thermal and compositional features established when
the core formed have largely controlled the subsequent evolution of the core and also
influence the evolution of the mantle, crust, and atmosphere.
CORE OF THE EARTH
CONCLUSION
We have the inner core, outer core, mantle and crust which play an important role on
Earth.
The layers of the Earth are responsible for the formation of our continents. Two Hundred
Fifty Million years ago most of the land mass was joined together forming a super
continent called Pangaea. Through the years we had continental drift, which is the
gradual movement and formation of continents (as described by plate tectonics).
Continents move an average of 2cm each year. Our seven continents look the way they
are because of continental drift.
The crust is very thin broken up in many pieces called plates, which float on the mantle.
These plates usually slide very smoothly, but sometime stick and build up pressure and
the rock snaps. When this occurs we get Earthquakes. Earthquakes can be important
because of Energy (seismic energy) released during Earthquakes provides much
information about the Earth’s interior. It helps us understand the changes in the earth
crust. Earthquakes also tell us if volcanoes are becoming more or less active.
The Hawaii Islands were formed because of hot spot. A volcanic hotspot is an area in the
upper mantle from which heat rises in a plume from deep in the Earth. High heat and
lower pressure at the base of the mantle facilitates melting of the rock. This melt, called
magma, rises through cracks to the surface and forms volcanoes. As the tectonic plate
moves over the stationary hot spot, the volcanoes are rafted away and new ones form in
their place.
Remember, the Earth is always changing, always moving. When two plates come
together, it is known as a convergent boundary, which is important in building
mountains where the Plates crash together to make mountains, such as the Himalayas.
Oceanic crust made of basalt is created through a divergent boundary, which occurs
when two tectonic plates move away from each other.
The cycle never stops and it ensures that the planet never runs out of rocks. Like a giant
recycling machine, Earth constantly creates rocks, breaks them down and converts them
into new types of rock. The Earth's crust recycles itself through subduction of crustal
material into the mantle and upwelling of magma from the mantle. These processes are
described by plate tectonics, a commonly accepted theory that explains the large-scale
movements of the Earth's lithosphere.

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GEOGRAPHY PROJECT-I

NAME – PRANAY SADANI

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