Transcript Conversations with the Earth

Conversations with the Earth
Tom Burbine
[email protected]
Quiz on Thursday
• Minerals
• Earth
• Magnetic Field
Earth
How do we determine
the composition of the
Earth’s interior?
Planetary densities
density 
weight
mass
volume
Volume = 4/3  r3
ρ = Mass/Volume
ρEarth = 5.515 g/cm3
Density (g/cm3)
Metallic iron
Basalt
Water
Cold ices and hydrogen
7.87
3.3
1.0
0.07-0.09
What do these densities tell us?
Density
(g/cm3)
Iron
7.87
Basalt
3.3
Water
1.0
Cold ices
0.07-0.09
Density
http://college.cengage.com/geology/resources/protected/physicallab/thelab/interior/index.htm
Earth’s Interior
Earth’s crust
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46.6% O
27.7% Si
8.1% Al
5.0% Fe
3.6% Ca
2.8% Na
2.6% K
2.1% Mg
Whole Earth
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32.1% Fe
30.1% O
15.1% Si
13.9% Mg
2.9% S
1.8% Ni
1.5% Ca
1.4% Al
Earth is made of minerals
How do we know what’s
in the interior of the Earth?
How do we know what’s
in the interior of the Earth?
• One way is Seismic Waves – vibrations created
by earthquakes
• http://abcnews.go.com/International/slideshow/63
-magnitude-earthquake-rocks-zealand-12970378
Seismic Waves
• P waves – primary waves
– (pushing) – travel faster
– can travel through
anything
• S waves – secondary –
(side to side) – travel
slower – only through
solids
Surface Waves
• Travel on the surface of the Earth
• Love Wave – side by side
• http://www.geo.mtu.edu/UPSeis/images/Love_ani
mation.gif
• Rayleigh Wave – rolling movement
• http://www.geo.mtu.edu/UPSeis/images/Rayleigh
_animation.gif
• Most of the shaking felt from an earthquake is due
to the Rayleigh waves
P (primary) waves
S (secondary) waves
Surface waves: Rayleigh and Love waves
Richter Scale
• Measures the magnitude of an earthquake
• Single number to quantify the amount of seismic energy released
by an earthquake. Amplitude of largest displacement
• Under 6.0 - At most slight damage to well-designed buildings.
Can cause major damage to poorly constructed buildings.
• 6.1-6.9 - Can be destructive in areas up to about 100 kilometers
across where people live.
• 7.0-7.9 - Major earthquake. Can cause serious damage over
larger areas.
• 8 or greater - Great earthquake. Can cause serious damage in
areas several hundred kilometers across.
How do we get information?
• The precise speed and direction of the waves
depends on the composition, density, pressure,
temperature, and phase (solid or liquid)
How can you study
the interior of a planet?
Density
• Density = mass/volume
• If the density is higher than the surface rock, there
must be denser material in the interior
Gravity
• If you can measure gravity (force) with a
spacecraft as it rotates around a body, you can
determine how mass is distributed on the body
Magnetic Field
• Tells if a planet has a molten metal interior
• Protects the Earth from charged particles
http://www.gcsescience.com/pme1.htm
Earth’s magnetic field is believed to be
caused by the convection of molten iron,
within the outer liquid core along with the
rotation of the planet
Electrons flow
http://geomag.usgs.gov/images/faq/Q6.jpg
http://www.scifun.ed.ac.uk/card/images/left/earth-magfield.jpg
• http://video.google.com/videoplay?docid=390246
6783636795302#
Geomagnetic Reversals
• Based upon the study of lava flows of basalt
throughout the world, it has been proposed that
the Earth's magnetic field reverses at intervals,
ranging from tens of thousands to many millions
of years
What may happen during the reversal?
• There may be a slight rise in the per capita cancer
rate due to a weaker magnetic field.
• We may also be able to see the northern lights at
lower latitudes
• If you own a compass, it will have difficulty
finding north until the magnetosphere settles.
Any Questions?