Download Density

Introduction to Physical Science
Monday, Wednesday, Thursday
Tom Burbine
[email protected]
Earth
How do we determine
the composition of the
Earth’s interior?
Planetary densities
density 
weight
mass
volume
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
•
•
•
•
•
•
•
•
46.6% O
27.7% Si
8.1% Al
5.0% Fe
3.6% Ca
2.8% Na
2.6% K
2.1% Mg
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?
• Seismic Waves – vibrations created by
earthquakes
Seismic Waves
• P waves – primary waves
– (pushing) – travel faster
– can travel through
anything
• S waves – secondary –
(side to side) – travel
slower – only through
solids
• http://alomax.free.fr/alss/examples/hodo/hodo_ex
ample.html
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)
Which of these bodies have they used
seismic waves to study?
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
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
• Magnetic pole moves
http://science.nasa.gov/headlines/y2003/29dec_magneticfield.htm
http://science.nasa.gov/headlines/y2003/29dec_magneticfield.htm
North Magnetic Pole
• However, the "north pole" of a magnet is defined
as the one attracted to the Earth's North Magnetic
Pole
• By this definition, the Earth's North Magnetic
Pole is physically a magnetic south pole
Glatzmeier and Roberts simulations:
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?
Any Questions?