Inside our earth

INSIDE OUR EARTH
KABITHA MADHU
PRINCIPAL
THE MERIDIN INTERNATIONAL
SCHOOL
TIRUCHENGODE

INSIDE OUR EARTH
The earth, our homeland is a dynamic planet. It is constantly
undergoing changes inside and outside. What is the earth made up of?

The radius of the
earth is 6371 km

CRUST
 The uppermost layer over the earth’s surface is called crust.
 It is the thinnest of all the layers.
 Its is about 35 km on the continental masses and only 5 km on the ocean floor.
 The main mineral constituents of the continental masses are silica and alumina
 It is thus called sial (si-silica and al-alumina)
 The oceanic crust mainly consist of silica and magnesium
 It is therefore called sima (si-silica and mi-magnesium)
 It forms 1 % of the volume of the earth

MANTLE
Just beneath the crust is the mantle
It extends up to a depth of 2900 km below the crust.
It forms 84 % of the volume of the earth
In terms of its constituent elements, the mantle is made up of
44.8% oxygen, 21.5% silicon, and 22.8% magnesium. There's also
iron, aluminum, calcium, sodium, and potassium. These elements
are all bound together in the form of silicate rocks, all of which
take the form of oxides.

CORE
The innermost layer of the earth is the core
It’s radius is about 3500 km.
It is mainly composed of nickel and iron and is called nife(ni-nickel
and fe-ferrous i.e. iron)
The central core has very high temperature and pressure.
It forms 15 % of the volume of the earth

Rocks & Minerals
The earth’s crust is made up of various types of rocks.
Any natural mass of mineral matter that makes up the earth’s
crust is called a rock.
Rocks can be of different colour, size and texture.
There are three major types of rocks:
Igneous rocks
Sedimentary rocks
Metamorphic rocks

Igneous Rocks
When the molten magma cools, it becomes solid.
Rocks thus formed are called igneous rocks.
Igneous rocks are also called primary rocks..
Igneous rocks are classified into two types of rocks.
Intrusive igneous rocks
Extrusive igneous rocks

Intrusice igneous rocks Extrusive igneous rocks
• Rocks inside the earth
• Plutonic rocks
• Formed from magma
• Usually dark coloured
• Usually dense
• Mafic: magnesium and iron
• Cools slowly
• Large grains
• E.g. granite. Grinding stone is
made of Granite.
• Rocks outside the earth
• Volcanic rocks
• Formed from lava
• Usually light coloured
• Usually low density. (light)
• Felsic: feldspar (aluminum)
• Cools quickly
• Small or no grains (fine or glassy
• E.g. basalt. Deccan plateau is
made of Basalt.

Sedimentary Rocks
Rocks roll down, crack and hit each other and are broken down into
small fragments called sediments. This sediment is
often formed when weathering and erosion break down
a rock into loose material in a source area.
These sediments are transported and deposited by wind, water, etc.
these loose sediments are compressed and hardened to form layers
of rocks called sedimentary rocks.
Sandstone is made from grains of sand, shale from clay
Sedimentary rocks may also contain fossils of plants, animals and
other micro-organisms that once lived on them.
.

Metamorphic Rocks
Igneous and sedimentary rocks can change into metamorphic rocks under
great heat and pressure .
Clay changes into slate
Limestone to marble
Granite to gneiss
Sandstone to Quartzite
Shales that are subject to heat and pressure of metamorphism alter into a
hard, fissile, metamorphic rock known as slate. With continued increase
in metamorphic grade the sequence is phyllite, then schist and finally
gneiss.

Inside our earth

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