- L-2 Geomorphology 5th June - Class PPT.pdf

INTERIOR OF THE EARTH
Why do we need to know about this?
● Understanding the earth's interior is essential to
understanding the nature of changes that take place over
and below the earth's surface.
● To understand geophysical phenomena like volcanoes,
earthquakes, etc.

Why do we need to know about this?
● To understand the internal structure of various objects of
the solar system.
● To understand the evolution and present composition of
the atmosphere.
● Future deep-sea mineral exploration etc.

Sources
● Direct Sources: Facilitate direct observation of what’s under the
surface.
○ Deep Earth mining and Drilling (deepest mine: Mponeng
gold mine and TauTona gold mine in South Africa at 3.6km;
deepest drilling 12 km in Kola peninsula, Russia).
○ Volcanic Eruptions: Bring the material inside the Earth to
the surface, giving us an insight into what is present under
the Earth.

Sources
● Indirect Sources: Help us statistically extrapolate what’s inside the Earth.
○ Meteors and other celestial bodies (other planets, moons, etc): Similar
formation Process as Earth. So, the internal structure of these bodies will be
similar to that of the Earth. Helps in expanding our imagination as to how
Earth would look from the inside.

Sources
○ Gravitation: Gravity value is not the same everywhere, and
this is known as a gravitational anomaly; helps us identify
material distribution inside the earth. Wherever heavier
materials have accumulated, gravitational force will be
higher as it is directly proportional to the mass of the
bodies in question.

Sources
○ Shifts in our magnetic fields: Our magnetic field constantly keeps
moving. It reverses in approximately 200000 to 300000 years. It is the
material inside the earth that is responsible for the magnetic field. This
reversal gives us the idea that the material inside the earth can move.
○ Earthquake waves: Body waves that are generated during earthquakes
are by far the best indirect source of information. (Details in the
earthquake section.)

● Other minor sources and observations:
○ Volcanic eruptions and existence of hot springs, geysers etc. point to
an interior which is very hot.
○ The high temperatures are attributed to automatic disintegration of
the radioactive substances.
○ Gravitation and the diameter of the earth helps in estimating
pressures deep inside

● Earth’s layers are identiﬁed by
studying various direct and indirect
sources.
● The structure of the earth's interior is
made up of several concentric layers.
● Broadly based on chemical properties,
three layers of earth can be
identiﬁed— crust, mantle, and core.
LAYERS OF EARTH

Crust Mantle Core
LAYERS OF EARTH

● The outer thin layer of the Earth.
● It has 2 parts: the denser oceanic
(basaltic) and the lighter
continental (granitic) crust.
● The outer covering of the crust is of
sedimentary material (granitic
rocks) and below that lie crystalline,
igneous and metamorphic rocks
which are acidic in nature.
Crust: 30-50km.

● The lower layer of the crust consists of basaltic and ultra-basic
rocks.
● Oceanic crust (SiMa) denser and thinner (5-30 km)
● Continental Crust (SiAl) lighter and thicker (50-70 km).
● The continental crust is thicker in the areas of major mountain
systems. It is as much as 70 -100 km thick in the Himalayan
region.
● The continental and the oceanic crusts are separated by the
Conrad discontinuity.
● It forms 0.5-1.0 per cent of the earth’s volume.
Crust: 30-50km.

● Mohorovicic Discontinuity to 2900 km (Gutenberg
Discontinuity).
● It forms 83% of Earth’s volume.
● Denser than crust (upper is 2.9-3.3g/cm3; lower is
3.3-5.7g/cm3; average density 4.5g/cm3).
● The crust and the uppermost part of the mantle are called
LITHOSPHERE. Its thickness ranges from 10-200 km. It is
Brittle in nature.
Mantle

● Below the Lithosphere lies the ASTHENOSPHERE, till 400 km
depth. It is a semi-solid molten layer, entirely within the mantle.
This layer is the source of Magma.
● The lower mantle extends beyond the asthenosphere. It is in
solid state.
● The upper and the lower mantle are separated by Repetti
Discontinuity.
● The mantle and the core are separated by Gutenberg
Discontinuity.
Mantle

● Lies between 2900 km and 6400 km below the earth's surface.
● It accounts for 16 per cent of the earth's volume.
● Core has the heaviest mineral materials of the highest density.
● It is composed of nickel and iron [NiFe].
● The outer core is liquid while the inner core is solid.
● They are separated by Lehmann’s Discontinuity.
Core: 2900-6400km

● The places inside the Earth’s crust where the seismic waves
experience an abrupt change in their velocities and/or
direction.
Discontinuities

Composition of Core & the Earth

Q.1) How does the Juno Mission of NASA help to understand
the origin and evolution of the Earth?
(2017, 10m)
PYQ

- L-2 Geomorphology 5th June - Class PPT.pdf

- L-2 Geomorphology 5th June - Class PPT.pdf

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