4. 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
5. 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.
6. 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
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14. 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
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16. 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
17. 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.
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23. 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.
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30. 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.