Planet Earth:
An Owner’s Manual
Earth’s Interior - Structure
and Composition
Unlike the Moon, the Earth is a
dynamic, constantly changing planet.
How do we know this?
• Lack of surface impact craters.
• Global volcanic activity.
• Global seismic activity.
• High mountains in spite of vigorous erosion
cause by surface water and atmosphere.
What’s going on inside the planet to
generate and maintain all of this
activity?
Questions for Discussion
Is the composition
of the deep interior
of the Earth different
than the exterior?
LR
How do we
investigate the
properties of the
deep Earth?
LF
What is the
Earth’s internal
energy source?
RR
What is the
Earth’s external
energy source?
RF
The density of the crust of the Earth does
not match the density of the whole planet.
• Continents
• Granite
• Quartz
d = 2.7 gm/cm3
• Ocean Basins
• Basalt
d = 6.0 gm/cm3
d = 3.0 gm/cm3
The Earth must be layered.
Dwhole =
2 layers:
Vouter = Vinner
€
Dinner + Douter
2
6=
Dinner + 3
2
What is the approximate
density of the Earth’s
hypothetical inner layer?
€
We know the Earth is layered and
composed of dense material on the
inside - how do we learn more?
Composition of meteorites (broken up
remnants of other rocky planets)
Samples of the deep Earth brought to the
surface by volcanism and plate tectonic
collisions
“X-raying” of the deep Earth using
earthquake waves (seismology).
Cape York meteorite - a 30-ton iron
meteorite that crashed into Greenland
10,000 years ago.
Iron meteorites are remnants of the
cores of planets that broke up early
in the history of the Solar System.
Kimberlite is a
volcanic rock
derived from the
deep interior of
the Earth that
contains xenoliths
of mantle rock.
Mantle Xenolith
Kimberlite pipes are mined for
the diamonds found in their
mantle xenoliths.
Udachnaya pipe in the Daldyn-Alakit kimberlite
field in Sakha Republic, Russia
Seismic waves: generated by
earthquakes or explosions.
Fault: fracture in rock along which
there is movement.
Normal Fault
Fault: fracture in rock along which
there is movement.
Strike Slip Fault
Left lateral fault - strike slip
Buildup of strain along an active fault
fault
Friction prevents movement at fault.
Buildup of strain along an active fault
fault
Buildup of strain along an active fault
fault
Buildup of strain along an active fault
fault
Buildup of strain along an active fault
fault
Rupture along the fault releasing strain energy
fault
Earthquake
vibrations
Seismic waves: generated by
earthquakes or explosions.
P waves arrive first
S waves second
Surface waves last
Seismic Waves
(6 km/sec)
Similar to sound waves can travel through liquids
Seismic Waves
s wave (3.5 km/sec)
Cannot travel through liquids
Seismic
evidence for
depth of
the Earth’s
core and
abrupt
change in
density.
Seismic
evidence
for the
existence
of a liquid
outer core.
S
Internal
Structure of
the Earth
Lithosphere
Asthenosphere
Internal Heat -Nuclear Fission
•Radioactive
elements present in the Earth were
acquired during its formation 4.6 billion years
ago.
•Uranium,
Potassium, Rubidium, Thorium decay
into smaller, stable elements such as Lead.
•Releases
high energy particles that collide with
and heat up other atoms.
•Internal
heat source is a radioactive battery slowly running down.
•Some
still remains from the kinetic energy
acquired during the formation of the Earth.
Both pressure and temperature
increase steadily from the
surface down to the Earth’s
center.
aesthenosphere
mantle
core
outer
rock
Pressure changes the
melting temperature of
both rock and iron.
inner
At higher pressures a
higher temperature is
required to melt rock
and iron.
iron
The physical state
(solid / partially solid /
liquid)
of the different layers of the
Earth depends on which is
higher - the melting
temperature or the actual
temperature.
aesthenosphere
The melting point of
both rock and iron
increases with depth.
mantle
rock
p.sol.
solid
core
outer
inner
iron
liquid
What will happen to the
size of the inner core and
the asthenosphere of the
Earth as the interior
continues to cool over
time?
aesthenosphere
A=M A<M A>M
mantle
core
outer
rock
inner
iron
The core and the
asthenosphere will both
become completely solid.
aesthenosphere
What will happen to the
core and the asthenosphere
of the Earth as the interior
continues to cool over
time?
mantle
core
outer
rock
inner
iron