Transcript 2-Unit4Part2EarthsInteriors

The Structure of the
Earth
The Earth’s Interior:
Methodology
Earth’s Interior
• How do we know what it is like today?
– Drilling
• Most drilling includes the upper 7 km of crust
• Deepest well: Soviet – 12 km deep
– 5 yrs, 7 km; 9 yrs, 5 km; then it got stuck
– Cost $100 million dollars
– Temperature 190oC
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Volcanic Activity
Laboratory experiments
Meteorites
Seismic Wave studies
Meteorites: Evidence about the Interior
• Meteorites
– Fragments of asteroids and small early planets (planetesimals)
that broke up as a result of collision with other solid bodies
• Composition of Meteorites
– Divisions
• 1. Iron-nickel meteorites
– From core of original bodies??
• 2. Stony meteorites
– Original body area like our mantle
• 3. Stony-iron meteorites
– 3 subclasses:
» Chrondrites
» carbonaceous chondrites
» achondrites
– From the cores and mantle of asteroids & planetismals
Iron-nickel meteorites
90% iron
• 9% nickel
•
.
Stony Meteorite
Stony-iron meteorites
Seismology: Evidence of the Earth’s
Interior
• Seismology
– The scientific study of earthquake
– The key to understanding the Earth’s
interior
Seismic Waves
• What are they?
– Vibrations in the body of the Earth
• How are they generated?
– Naturally
• Earthquakes
• Volcanoes
• Impacts
– Artificially
• Explosions
• Mechanical devices
Seismic Waves: Measuring
• Seismograph
– Thousands of stations are set up
worldwide
– Used to locate earthquake
– Simple pendulum
• When the ground shakes, the base
and frame of the instrument move
with it
• Inertia keeps the pendulum in place
• It will then appear to move; relative
to the shaking ground
• As it moves, it records the pendulum
displacement
• The tracing is called a seismogram
– Networks of seismograph stations
are used to determine the location of
the earthquake
• Seismology and the Science of
Earthquakes – Waves – Magnitude –
and the Richter Scale
• (3:22 minutes)
Seismic Waves: Terms
• Earthquake
– Release of stress build up along a fault
– Slipping and moving of rocks along a fault
• Focus
– The origin of seismic waves
– The energy of seismic waves is released from this point
• Epicenter
– The point on the earth’s surface directly above the focus
• Fault
– Crack or break in the earth’s crust
– Surface along which rocks move
• Waves:
– P waves
– S waves
– L waves
Seismic Waves
• 3 Main Types released by Earthquakes:
1. P-waves (Primary / Compression waves)
• Longitudinal / compressional wave
– Alternately push (compress) and pull (dilate) the rocks
through which they pass
» Squeezes and stretches the material in the same
direction
– Generated by the Focus
• Fastest of the waves
• Propagates through solids, liquids and gases
2. S-waves (Secondary / Side-to-side waves)
• Transverse waves
– Generated by the Focus
• Slower wave
• Moves material at right angles to the wave
direction
• Propagate only solids
Animation of P and S Waves
• http://www.classzone.com/books/earth
_science/terc/content/investigations/es
0402/es0402page05.cfm
• http://www.classzone.com/books/earth
_science/terc/content/visualizations/es
1002/es1002page01.cfm?chapter_no=
visualization
Visualization of an Earthquake
• http://www.pbs.org/wnet/savageearth/a
nimations/earthquakes/flash.html
3. L-waves (Long waves or Love Waves)
• Surface waves that cause horizontal shearing of the
ground
– Travel on the surface of the earth and shake rocks
sideways as they move across the surface
– Generated by the epicenter
– Particles travel in a rolling motion
– Note:
• Surface waves cause the most damage
• Not used to determine Earth’s interior
Locating The Epicenter
• P and S waves travel at different rates
– This helps determine the distance to the
epicenter
• P waves will always arrive at a seismic
station first
– The distance of the P wave ahead of the S
wave depends on how far away the
earthquake is
• Key: The further away the epicenter,
the wider the gap between the P and S
waves.
Earthquake
• http://earthquake.usgs.gov/eqcenter/
• Predicting Earthquakes
• Video 2 minutes
• Earthquakes
• Video 3 minutes
Seismic Topography
Volcanoes: Evidence of the Earth’s
Interior
• Referred to as “Windows into the
Earth’s Interior.” Why?
• Volcanoes erupt material that is tens to
hundreds of kilometers into the Earth
– Deepest rock samples of the Earth’s
interior are volcanic rock
Importance of Earth Hot Interior
• Seismic activity – earthquake, volcano
• Magnetic field (Geomagnetism)
– Generated by the movements of the molten iron and
nickel layer in the outer core
– Convection current in this electrically conducting
fluid act as a Dynamo*
• Fluid acts to generate and maintain the magnetic field
• * Dynamo theory
– Process through which motion of a conductive body in the
presence of a magnetic field acts to regenerate the magnetic
field
– Note: Without this Dynamo effect, the magnetic
field would die out within 10 000 years
Importance of Earth Hot Interior
• Interior heat powers convection current
of the asthenosphere which in turn
allows the lithosphere to move (plates
moving)
– Result:
•
•
•
•
formation of mountain ranges
deep sea trenches
Volcanic belts
Earthquake zones
• May be linked to long-term climatic
changes