Internal Structure of The Earth Physical Layering Determining the Earth's Internal Structure C. The Earth's Internal Layered Structure and Composition D. VELOCITY AND DENSITY VARIATION WITHIN THE EARTH The immense amount of heat energy released from gravitational energy and from the decay of radioactive elements melted the entire planet, and it is still cooling off today. Denser materials like iron (Fe) sank into the core of the Earth, while lighter silicates (Si), other oxygen (O) compounds, and water rose near the surface. The earth is divided into four main layers: the inner core, outer core, mantle, and crust. The core is composed mostly of iron (Fe) and is so hot that the outer core is molten, with about 10% sulphur (S). The inner core is under such extreme pressure that it remains solid. Most of the Earth's mass is in the mantle, which is composed of iron (Fe), magnesium (Mg), aluminum (Al), silicon (Si), and oxygen (O) silicate compounds. At over 1000 degrees C, the mantle is solid but can deform slowly in a plastic manner. The crust is much thinner than any of the other layers, and is composed of the least dense potassium (K), calcium (Ca) and sodium (Na) aluminum-silicate minerals. Being relatively cold, the crust is rocky and brittle, so it can fracture in earthquakes.

1. Internal Structure of The EarthInternal Structure of The Earth
A. PHYSICAL LAYERING
A. DETERMINING THE EARTH'S INTERNAL
STRUCTURE
C. THE EARTH'S INTERNAL LAYERED
STRUCTURE AND COMPOSITION
D. VELOSITY AND DENSITY VARIATION
WITHIN THE EARTH

2. INTERNAL STRUCTURE OF THE EARTHINTERNAL STRUCTURE OF THE EARTH
• The immense amount of heat energy released from gravitational energy and
from the decay of radioactive elements melted the entire planet, and it is still
cooling off today. Denser materials like iron (Fe) sank into the core of the
Earth, while lighter silicates (Si), other oxygen (O) compounds, and water
rose near the surface.
• The earth is divided into four main layers: the inner core, outer core, mantle,
and crust. The core is composed mostly of iron (Fe) and is so hot that the
outer core is molten, with about 10% sulphur (S). The inner core is under
such extreme pressure that it remains solid. Most of the Earth's mass is in the
mantle, which is composed of iron (Fe), magnesium (Mg), aluminum (Al),
silicon (Si), and oxygen (O) silicate compounds. At over 1000 degrees C, the
mantle is solid but can deform slowly in a plastic manner. The crust is much
thinner than any of the other layers, and is composed of the least dense
potassium (K), calcium (Ca) and sodium (Na) aluminum-silicate minerals.
Being relatively cold, the crust is rocky and brittle, so it can fracture in
earthquakes.

3. Major Structural unit of the earthMajor Structural unit of the earth
• Three major structural unit/ layers of the earth
• 1. CRUST
• 2. MANTLE
• 3. CORE
These structures are divided on the basis of
seismic waves (P and S wave velocities)

5.  Outer most and thinnest layer
 Its relatively cool and consist of hard rocks
 Oceanic crust is about 5-10 km thick, basaltic
composition dominated by silica and magnesium (SiMa)
 Continental crust is about 20-40 km thick but under
mountain it can be 70 Km thick, composition is granitic
( Silica and Al dominantly).
Crust

7. MantleMantle
• The mantle lies directly below the crust.
• It is almost 2900 kilometers thick and makes up 80 percent
of the Earth’s volume.
• Chemical composition may be similar throughout the
mantle
• Temperature and pressure increase with depth resulting
strength of mantle rock to vary with depth, and
• create layering within the mantle.
• The upper part of the mantle consists of two layers
1) Lithosphere
2) Asthenosphere

8. CoreCore
• Core is the innermost of the Earth’s layers.
• Outer core: 2900 to 5150 km (liquid)
• Inner core: 5150 to 6370 km ( solid)
• Over all it is a sphere with a radius of about 3470 kilometers and is
composed largely of iron and nickel and have a density about 12 x
103
Kg/m3
• In the boundary of outer core P- waves is marked by an abrupt
reduction in the velocity and bent inwards and producing shadow
zone as well by the disappearance of S- waves, it may be
concluded that it is in liquid state (molten) because of the high
temperature in that region.
• Near its center, the core’s temperature is about 6000ºC, as hot as
the Sun’s surface. The pressure is greater than 1 million times that
of the Earth’s atmosphere at sea level.
• This extreme pressure overwhelms the temperature effect and
compresses the inner core to a solid.

9. LithosphereLithosphere
• Outer part of the Earth including both
the uppermost mantle and the crust,
make up the lithosphere
• its mechanical behavior is similar to
that of the crust.
• The lithosphere can be as thin as 10
kilometers where tectonic plates
separate. The lithosphere is about
75 kilometers thick beneath ocean
and 125 kilometers under the
continents.
• A tectonic (or lithospheric) plate is a
segment of the lithosphere.

10. • The asthenosphere extends from the base of the lithosphere to a
depth of about 350 kilometers.
• Increasing temperature with depth gradually , as a result small
degrees of partial melting, possibly as much as 10% in regions of
high heat flow. This partial melt is an important source of magma
and a lubricant to ease the tectonic movements of the lithospheric
plate.
• This change in rock properties occurs over a vertical distance of
only a few kilometers.
• This zone also called as low velocity zone where the velocities of s
wave is decrease.
• So the asthenosphere flows slowly, perhaps at a rate of a few
centimeters per year (Lithospheric plates glide slowly over the
asthenosphere like sheets of ice drifting across a pond )
• At the base of the asthenosphere, increasing pressure causes the
mantle to become mechanically stronger, and it remains so all the
way down to the core.
AsthenosphereAsthenosphere

12. Interior of the EarthInterior of the Earth

13. Physical LayeringPhysical Layering
• Because of variations in temperature and in pressure, the materials inside the earth
vary in their physical properties with depth.
• Inner Core is the central part of the iron-nickel core. It is a solid iron sphere. The
reason that the iron is solid is that the pressure at the center of the earth is
significantly higher than the pressure above, while the temperature is only slightly
higher. While higher temperature would tend to melt materials, higher pressures
tend to create solids.
• Outer Core constitutes the remainder of the iron-nickel core and is liquid. It is liquid
because the pressure is lower.
• Mesosphere: The majority of the mantle from the core-mantle boundary is solid
and is called the mesosphere.
• Asthenosphere: Nearer to the surface of the earth the temperature is still relatively
high but the pressure is greatly reduced. This creates a situation where the mantle
is partially melted. The asthenosphere is a plastic solid in that it flows over time.
• Lithosphere: Above the asthenosphere, the temperature begins to drop more
rapidly. This creates a layer of cool, rigid rock called the lithosphere. The
lithosphere includes the uppermost part of the mantle and it also includes all of the
crust. That is, the crust is the upper part of the lithosphere, and the upper mantle is
the lower part of the lithosphere.

14. Internal Structure of the EarthInternal Structure of the Earth
• The Divisions of
Inner Space
• Size of the Earth
– Radius = 6370 km
– Diameter = 12,740
km

15. Determining the Earth's Internal StructureDetermining the Earth's Internal Structure
• Earth has a layered structure. The boundaries between the layers are
called discontinuities.
• The layered structure is determined from studies of how seismic waves
behave as they pass through the Earth. P- and S-wave travel times
depend on properties of rock materials through which they pass.
Differences in travel times correspond to differences in rock properties.
• Seismic wave velocity depends on the density and elasticity of rock.
Seismic waves travel faster in denser elastic rocks.
Speed of seismic waves increases with depth (pressure, density and
elasticity increase downward).
• It can be seen in the paths of the P- and S-waves as they travel through
the Earth in the diagram below.

16. SHADOW ZONESSHADOW ZONES

17. Refraction of seismic waves as they travelRefraction of seismic waves as they travel
through the Earththrough the Earth

18. Refraction of seismic waves as theyRefraction of seismic waves as they
travel through the Earthtravel through the Earth
• Note the curved wave paths indicating gradual increases in density
and seismic wave velocity with depth. Also note the sharp refraction
(bending of waves) at the discontinuities or boundaries between
layers.
• Note the shadow zones. There is a large S-wave shadow zone
(labelled " No direct S-waves" ) extending across the side of the globe
opposite from the epicenter (from 105o
). S-waves cannot travel
through the molten (liquid) outer core.
• There is a smaller P-wave shadow zone, seen on both sides (gray
shading), from 105o
to 140o
. The P-wave shadow zone makes a ring
around the globe.
• Major layers of the Earth were detected before 1950.
Fine details were delineated in 1960's by observing the behavior of
seismic waves generated during nuclear testing.

19. The Earth's Internal Layered StructureThe Earth's Internal Layered Structure
and Compositionand Composition
• Crust
• Continental Crust (averages about 35 km thick; 60 km in
mountain ranges; diagram shows range of 20-70 km)
Granitic composition
• Oceanic Crust (5 - 12 km thick; diagram shows 7-10 km
average)
Basaltic composition
Thin layer of unconsolidated sediment covers basaltic igneous
rock.
Oceanic crust has layered structure (ophiolite complex)
consisting of the following:
– Pillow basalts (basalts that erupted sub-aqueously)
– " Sheeted dikes " - interconnected basaltic dikes
– Gabbro (coarse grained equivalent of basalt; cooled slowly)

20. The Earth's Internal Layered Structure and CompositionThe Earth's Internal Layered Structure and Composition
• Mantle (2885 km thick)
• Composition: peridotite (Mg Fe silicates), kimberlite (contains
diamonds), eclogite - based on studies of rock from mantle brought up
by volcanoes, from density calculations, and composition of stony
meteorites.
• Lithosphere - outermost 100 km of Earth . Consists of the crust plus the
outermost part of the mantle which is solid. Divided into tectonic or
lithospheric plates that cover surface of Earth .
• Asthenosphere - low velocity zone at 100 - 250 km depth in Earth
(seismic wave velocity decreases). Rocks are at or near melting point.
Magmas generated here. Solid that flows (rheid); plastic behavior.
Convection in this layer moves tectonic plates.
• Less is known about the mantle below the astheno-sphere.

21. The Earth's Internal Layered Structure and CompositionThe Earth's Internal Layered Structure and Composition
Outer core (2250 km thick)
• S-waves cannot pass through outer core, therefore we
know the outer core is liquid (molten).
• Composition: Molten Fe (85%) with some Ni, based
on studies of composition of meteorites.
Core may also contain lighter elements such as Si, S,
C, or O.
• Convection in liquid outer core plus spin of solid inner
core generates Earth's magnetic field.
Magnetic field is also evidence for a dominantly iron
core.

22. The Earth's Internal Layered Structure and CompositionThe Earth's Internal Layered Structure and Composition
• Inner core (1220 km radius)
• Solid Fe (85%) with some Ni - based on studies of
meteorites

23. VELOSITY AND DENSITY VARIATION WITHINVELOSITY AND DENSITY VARIATION WITHIN
THE EARTHTHE EARTH

25. Summary of the layers and discontinuities within theSummary of the layers and discontinuities within the
EarthEarth
Layer Thickness
(km)
Density
(g/cm³ ))
P-wave
velocity
(km/sec)
Continental crust avg. 35 2.6 - 2.86 6
Oceanic crust 5 - 12 3.0 - 3.5 7
Mohorovicic Discontinuity
Mantle 2885 4.5 - 10 8 - 12
Gutenberg Discontinuity
Core (average) 3470 - -
Outer core (liquid) 2250 10.7 or 12 8 - 10
Inner core (solid) 1220 13.5 11 - 12

26. AVERAGE COMPOSITION OF THEAVERAGE COMPOSITION OF THE
CRUSTCRUST
• Elemental abundances in the crust (% wt ).
0 SI Al Fe Ca Na K Mg Others
46.6 27.7 8.1 5.0 3.6 2.8 2.6 2.0 1.6

27. THANKSTHANKS

28. Thank You All