Interior of the earth

Department of Geology
Guided by Presented by
Prof. Lalsingh Solanki Vishal Choudhary
Class –M.Sc. (1st sem.)
Govt. Holkar Science College Indore (M.P.)

 Introduction
 Compositional elements of the earth
 Interior of the earth
 Chemical composition and layering system of the
earth
 seismic waves
 seismic wave propagation
 Significance of seismic waves
 Comparison of earth internal structure with the
moon
 References

 Three centuries ago, the English scientist Isaac
Newton calculated, from his studies of planets and
the force of gravity, that the average density of the
Earth is twice that of surface rocks and therefore
that the Earth's interior must be composed of much
denser material. Our current information comes
from studies of the paths and characteristics of
earthquake waves travelling through the Earth, as
well as from laboratory experiments on surface
minerals and rocks at high pressure and
temperature.

 Other important data on the Earth's interior come
from geological observation of surface rocks and
studies of the Earth's motions in the Solar System, its
gravity and magnetic field, and the flow of heat from
inside the Earth. Earth is made up of three main shells:
the very thin, brittle crust, the mantle, and the core; the
mantle and core are each divided into two parts.
Although the core and mantle are about equal in
thickness, the core actually forms only 15 percent of
the Earth's volume, whereas the mantle occupies 84
percent.

 Carbon-containing compounds that either
occur in living organisms, or have
characteristics that resemble those of
molecules in living organisms, are called
organic chemicals. Examples include oil,
protein, plastic, fat, and rubber.
 ORGANIC CHEMICALS

 MINERAL: A solid substance in which atoms are
arranged in an orderly pattern is called a mineral..
 CRYSTAL: A single coherent sample of a mineral
that grew to its present shape and has smooth, flat
faces is a crystal.
 GRAIN: An irregularly shaped sample, or a
fragment derived from a once-larger crystal or group
of crystals, is a grain.
 GLASSES: A solid in which atoms are not arranged
in an orderly pattern is called glass. Glass forms
when a liquid freezes so fast that atoms do not have
time to organize into an orderly pattern.

 ROCKS : Aggregates of mineral crystals or grains, and
masses of natural glass, are called rocks. Geologists
recognize three main groups of rocks. (1) Igneous rocks (2)
Sedimentary rocks (3) Metamorphic rocks.
 METALS : Metals are opaque, lustrous elements that are
good conductors of heat and electricity.
 ALLOY : An alloy is a mixture containing more than one
type of metal atom (e.g., bronze is a mixture of copper and
tin).
 MELTS: Melts form when solid materials become hot and
transform into liquid. Molten rock is a type of melt.
 VOLATILES : Materials that easily transform into gas at
the relatively low temperatures found at the Earth’s surface
are called volatiles.

INTERIOR OF THE EARTH
THE CRUST
THE MANTLE
THE CORE

 Crust is the outer thin layer of rock which
forms a thin skin on the earth surface , with a
total thickness normally between 30-50 km.
 Crust is thinner beneath the oceans than
beneath the continent.
 Oceanic crust is thinner (5-30 km thick) as
compared to the continental crust (50-70 km
thick).
 The continental crust is thicker in the areas of
major mountain systems. -100 km thick in the
Himalayan region.

 Mohorovicic (Moho) discontinuity forms the
boundary between crust and
asthenosphere [asthenosphere is a part of mantle].
 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.
 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’).

CHARACTERSTICS OCEANIC CRUST CONTINENTAL
CRUST
AVERAGE
THICKNESS
7 Km 20 to 70 Km (thickest
under mountain)
seismic P- WAVES 7Km/Second 6 Km/Second (higher
in lower crust)
DENSITY 3.0 gm/(cm)3 2.7 gm/(cm)3
PROBABLE
COMPOSITION
Basalt underlain by
gabbro
Graite,other plutonic
rocks ,schist ,gneiss
(with sedimentary
rock cover)

 The Mantle extends from Moho’s
discontinuity (35 km) to a depth of 2,900 km
(Moho-Discontinuity to the outer core).
 The crust and the uppermost part of the
mantle are called lithosphere.Its thickness
ranges from 10-200 km.
 The lower mantle extends beyond the
asthenosphere.It is in solid state.
 The density of mantle 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.
 It forms 83 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.
 Earth's mantle plays an important role in the Evolution
of the crust and provides the thermal and mechanical
driving forces for plate tectonics.

The upper portion of the mantle is called
Asthenosphere.
The word astheno means weak.
It is considered to be extending up to 400 km.
It is the main source of magma that finds its
way to the surface during volcanic eruptions.
It has a density higher than the crust’s.

 Lies between 2900 km and 6371 km below the earth’s
surface.
 Accounts for 16 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.

 The core is the densest layer of the earth with its
density ranges between 9.5-14.5g/cm3.
 The Core consists of two sub-layers: the inner core
and the outer core.
 The inner core is in solid state and the outer core is in
the liquid state (or semi-liquid).
 The discontinuity between the upper core and the
lower core is called as Lehmann Discontinuity.
 Barysphere is sometimes used to refer the core of the
earth or sometimes the whole interior.

 The crust is covered by a thin layer of sedimentary
rocks of very low density.
 This layer is composed of crystalline rocks, mostly
silicate matter .
 The upper part of this layer is composed of light
silicate matter while heavy silicate matter dominated in
the lower part.
According to Suess

 Located just below the outer sedimentary cover
is composed of granites.
 Dominated by silica and aluminium, acid
materials and silicate of K ,Na and
Al(SIAL=SI+AL).
 The average density is 2.9 ,thickness ranges
between 50-300km.
 Continents have been formed by sialic layer.

 Composed of basalt and the sources of magma
and lava during volcano eruption.
 Dominated by silica and magnesium .
 Average density ranges between 2.9 to 4.7 and
thickness from 1,000 Km to 2,000 Km .
 There is abundance of basic matter .
 The silicate of Mg, Ca and Fe are most abundantly
found.

Composed of nickel (Ni) and iron (Fe) .
Made up of heavy materials have thus have
high density (11).
The diameter of this zone is 6880 km.
The presence of the iron indicates the
magnetic property of the earth interior.
This property also indicate the rigidity of
the earth.

 The different types of tremors and waves generated
during the occurrence of an earthquake are called
seismic WAVES .
 The place of the occurrence of an earthquake is called
FOCUS and the place which experiences the seismic
events first is called EPICENTRE which is located on the
earth surface and is always perpendicular to the focus.
 The deepest focus has been measured at the depth of 700
km from the earth surface .

 P-waves are the first waves to arrive on a complete record of
ground shaking because they travel the fastest.
 They typically travel at speeds between ~1 and ~14 km/sec.
 The slower values corresponds to a P-wave traveling in
water, the higher number represents the P-wave speed near
the base of Earth's mantle.
 The velocity of a wave depends on the elastic properties and
density of a material.
 The vibration caused by P waves is a volume change,
alternating from compression to expansion in the direction
that the wave is traveling.
 P-waves travel through all types of media - solid, liquid, or
gas.

 Secondary , or S waves, travel slower than P waves and are
also called "shear" waves because they don't change the
volume of the material through which they propagate, they
shear it. S-waves are transverse waves because they vibrate
the ground in a the direction "transverse", or
perpendicular, to the direction that the wave is traveling.
 Typical S-wave propagation speeds are on the order of 1 to
8 km/sec.
 The lower value corresponds to the wave speed in loose,
unconsolidated sediment, the higher value is near the base
of Earth's mantle.
 An important distinguishing characteristic of an S-wave is
its inability to propagate through a fluid or a gas because a
fluids and gasses cannot transmit a shear stress and S-
waves are waves that shear the material.

 Love waves are transverse waves that vibrate
the ground in the horizontal direction
perpendicular to the direction that the waves
are traveling.
 They are formed by the interaction of S waves
with Earth's surface and shallow structure and
are dispersive waves.
 The typical range of velocities is between 2 and
6 km/second.
 The amplitude of ground vibration caused by a
Love wave decreases with depth - they're
surface waves. Like the velocity the rate of
amplitude decrease with depth also depends on
the period.

 Rayleigh waves are the slowest of all the seismic
wave types and in some ways the most
complicated.
 Like Love waves they are dispersive so the
particular speed at which they travel depends on
the wave period and the near-surface geologic
structure, and they also decrease in amplitude with
depth.
 Typical speeds for Rayleigh waves are on the order
of 1 to 5 km/s.

 Several types of interaction between waves and
the subsurface geology (i.e. the rocks) are
commonly observable on seismograms.
 Refraction
 Reflection
 Dispersion
 Diffraction
 Attenuation

 A shadow zone is where waves of certain
types don’t reach the surface relative to another
place on the surface (about 105 degrees from
center). The refraction properties at the
boundaries between each layer create this
“shadow zone,” from which geologists can
infer that there is a liquid layer of the core (the
outer layer).The Earth has to have a molten,
fluid core to explain the lack of S waves in the
shadow zone, and the bending of P waves to
form their shadow zone.

 Study the internal structure of the earth.
 Identifying the oil traps.
 Identifying the ground water level.
 Study the Earthquake .

 All of the terrestrial planets have a three-part
layered structure. At the center is a metallic, iron-
rich core, part of which may be molten. Above the
core is a thick middle layer called the mantle, made
of silicate rock (composed mostly of silicon, oxygen,
iron, and magnesium), making up most of the bulk
of the planet. Above the mantle is a relatively thin
crust of less-dense rocky material. The crust has
more lighter elements (aluminum, sodium, calcium,
sulfur) than the mantle

 "We applied tried and true methodologies from
terrestrial seismology to this legacy data set to
present the first-ever direct detection of the
moon's core," said Renee Weber, lead
researcher and space scientist at NASA's
Marshall Space Flight Center in Huntsville,
Ala.

hthand
Apollo 11 astronaut Buzz
Aldrin with the seismic
experiment. Solar panels
have deployed on the left
and right and the antenna
is pointed at Earth. The
laser reflector is beyond
the antenna and, in the
distance, the TV camera is
silhouetted against the
black sky. The stereo close-
up camera is near the
righthand edge of this
detail .
BY – NASA

1. Diane H.Carlson; Charles C. Plummer; Lisa
Hammersley; 2010. Physical Geology: Earth Revealed ,
Ninth Edition; McGraw Hill companies.
2. Stephen Marshal (2008). Earth: Portrait of a Planet
Third Edition; W.W Nortan & Company.
3. Singh Savindra (2015). Physical Geography By
Pravalika Publications Allahabad.
4. https://www.nasa.gov/
5. http://eqseis.geosc.psu.edu/~cammon/HTM
L/Classes/IntroQuakes/Notes/waves_and_in
terior.html

Interior of the earth

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Interior of the earth