Download Chapter12 EarthsInterior

Chapter 17
Earth’s interior
Earth’s interior structure
• Earth is composed of three shells;
–Crust
–Mantle
–Core
Earths interior and seismic waves
• The study of earth’s interior can be
done by;
–Direct sampling
–Indirect methods
– Indirect methods
• Meteorites
• Seismic waves (P and S)
• P-waves can pass through all
materials (solids and fluids)
• S-waves can only pass through
solids.
The crust
• Outermost layer of the earth
forming a thin skin. Divided into 2
parts;
–Continental crust
–Oceanic crust
• Mantle:
–upper mantle and
–lower mantle
• Upper mantle and crust constitute
Lithosphere where the rocks are in
rigid form.
• Lower mantle is also called
Asthenosphere where the rocks
are in plastic state.
• The boundary between the crust
and mantle is called the Moho.
The Core
• Is there really a core?
–Combined Density of the crust
and mantle is less than that of
the whole earth.
–S-waves shadow zone
The Core
• Core is divided into 2 parts;
–The outer core is about 2,250 km
thick, composed of molten iron
and nickel.
–The inner core is probably solid
iron and nickel at about 5000° C.
What is isostasy?
• It’s a balance or equilibrium of the
earth’s crust floating on the dense
mantle.
• Can be compared with wooden
blocks floating on water. The
higher the wood block appears, the
deeper its root.
• Erosion of continental crust shows
isostatic equilibrium.
• Erosion of glacial ice shows
isostatic equilibrium in the form of
crustal rebound.
Physical properties of Earth
• Gravity
• Magnetism
• Heat flow
• Gravity: gravitational attraction
exists among all bodies in the
universe
• Gravity anomalies: abnormal
gravity readings.
–Positive anomaly: gravity reading
higher than the regional gravity
readings
–Negative anomaly: gravity
readings lower than the regional
gravity readings
• Magnetism: the earth acts like a
giant dipolar magnet.
• Magnetic poles: oriented 11.5° from
the geographic poles.
–North pole
–South pole
• Magnetometer is used to measure
magnetic strength.
Source of magnetism
• the convection currents in outer
liquid core produce electric
currents and any electric field is
associated with a magnetic field.
• Normal and reversed polarity
• Paleomagnetism: the study of
ancient magnetism preserved in
rocks.
• Magnetic anomalies
–Positive
–Negative
• Heat flow: the rate at which
temperature increases within the
earth is called Geothermal
gradient.
• 25° C/km at shallow depths (crust)
but drops to 1°C/km within the
mantle.
• Sources of heat inside the earth:
–Radioactivity
–Rising magma bodies
–Gravitational energy from
accretion.