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Earth’s IntErIor
Contents
1.Evidences of earth’s interior
2.Structure of the earth’s interior
Why know about Earth’s Interior
• To understand Volcanism, Earthquakes and various other
geophysical phenomenon
• To undertand the internal structure of other Solar System
objects
• To understand the formation of atmosphere and its present
composition
• Mineral Exploration
Things that we know about Earth’s Interior
• Earth’s interior is a heterogeneous medium
• Earth’s interior consists of several concentric layers of varying physical and chemical
properties
• Temperature increases with depth
• Density of the Earth’s interior increases with depth
• Earth’s interior is divided into different layers namely
1.
Crust
 Continental crust
 Oceanic crust
 Moho-Discontinuity (Mohovoricic Discontinuity)
2.
Mantle
 Asthenosphere
3.
Core
 Outer Core (Liquid)
 Inner Core (Solid)
Evidences about Earth's Interior
• Evidence From The Meteorites
• Volcanic eruptions, springs and gyesers
• Behaviour of Earthquake Waves (Sesmic Waves)
Volcanic eruptions, springs and gyesers
• High Levels of Temperature and Pressure Downwards
The high temperatures are attributed to automatic
disintegration of the radioactive substances
Evidence From The Meteorites
• When they fall to earth, their outer layer is burnt during
their fall due to extreme friction and the inner core is
exposed.
• The heavy material composition of their cores confirms the
similar composition of the inner core of the earth, as both
evolved from the same star system in the remote past.
Evidences from Earthquake waves
•
•
1.
2.
3.
Earthquake waves give a much better picture about
earth’s internal structure
The earthquake waves are measured with the help of
a seismograph and are of three types—
the 'P' waves or primary waves (longitudinal nature),
secondary waves or 'S' waves (transverse in nature)
surface waves are long or ‘L’ waves (transverse in
nature).
Primary Waves (P waves)
 longitudinal or compressional waves.
 These waves are of
 high frequency
 short wave length
 They can travel in both in solids and liquids
 travels with fastest speed through solid and more dense materials
 In liquid materials, their speed is slowed down.
Secondary Waves (S waves)
 transverse or distortional waves.
 analogous to water ripples or light waves
 A secondary wave cannot pass through liquid materials.
 These waves are of
 high frequency,
 short wave-length waves
 travel at varying velocities (proportional to density)
 The shallow zone of 'S' waves extends almost halfway around the globe
Surface Waves (L waves)
 Also long period waves.
 generally affect the surface of the Earth only and die out at smaller depth.
 The are
 low frequency,
 long wavelength, and
 transverse vibration
 develop in the immediate neighbourhood of the epicenter.
 These waves are responsible for most the destructive force of earthquake.
 recoded in the last at the seismograph.
 The L waves do not pass and do not go deeper inside the earth.
3D view of P and S waves: https://www.youtube.com/watch?v=2Wlh3M2a10U
Behaviour of P and S waves while
passing through earth’s interior
Behaviour of P and S waves while
passing through earth’s interior
If earth was a homogeneous medium
Behaviour of P and S waves while
passing through earth’s interior
Layers of the Earth
 The structure of the earth's interior is layered. It is made up of several concentric
layers
 broadly three layers can be identified—crust, mantle and the core.
Layers based on chemical and physical properties
(1)crust,
(2)mantle, and
(3)core.
Seismic Discontinuities
• Mohorovicic Discontinuity (Moho) - separates the crust from the mantle
• A soft asthenosphere (highly viscous, mechanically weak and ductile)
• Gutenberg Discontinuity - lies between the mantle and the outer core
The Crust
 Continental Crust – 100 km thick; Oceanic Crust – 35 km thick
 It forms 0.5-1.0 per cent of the earth's volume.
 Part of the Earth above the Mohorovicic (Moho) discontinuity.
 The outer covering of the crust is of sedimentary material (granatic rocks) and
below that lie crystalline, igneous and metamorphic rocks which are acidic in
nature.
 The lower layer of the crust consists of basaltic and ultra-basic rocks
 The continents are composed of lighter silicates—silica + aluminium (also
called `sial—while the oceans have the heavier silicates—silica + magnesium
(also called `sima'), which form a part of the mantle.
Mantle
 Moho-Discontinuity to the core.
 The depth of mantle varies between 35 km and 2900 km.
 The density varies between 2.9 and 3.3.
 The density ranges from 3.3 to 5.7 in the lower part.
 It is composed of solid rock and magma
 forms 16 per cent of the earth's volume.
 The outer layer of the mantle is partly simatic while the inner
layer is composed of wholly simatic ultra-basic rocks.
Core
 lies between 2900 km and 6400 km below the earth's surface
 accounts for 83 per cent of the earth's volume.
 core has the heaviest mineral materials of highest density.
 It is composed of nickel and iron [nife]
 The outer core is liquid while the inner core is solid.
 a zone of mixed heavy metals + silicates separates the core
from outer layers.
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