Transcript 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?