Introduction to Physical Science

Monday, Wednesday, Thursday

Tom Burbinetomburbine@astro.umass.edu

EarthHow do we determine the composition of the

Earth’s interior?

Planetary densities

volumeweightdensity mass

ρ = Mass/VolumeρEarth = 5.515 g/cm3

Density (g/cm3)Metallic iron 7.87Basalt 3.3Water 1.0Cold ices and hydrogen 0.07-0.09

Density (g/cm3)

Iron 7.87

Basalt 3.3

Water 1.0

Cold ices 0.07-0.09

DensityWhat do these densities tell us?

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_example.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) wavesS (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

http://geomag.usgs.gov/images/faq/Q6.jpg

Electrons flow

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?