2. Seismic waves- Earthquake waves travel differently as they move through different materials Through some materials they move straight, while others will bend waves Scientists study these waves to determine what makes up the interior of our Earth http://www.classzone.com/books/earth_science/terc/co ntent/visualizations/es1009/es1009page01.cfm http://www.classzone.com/books/earth_science/terc/co ntent/visualizations/es1009/es1009page01.cfm

3. 3 major zones defined by chemical composition 1. Crust Thin outer rocky layer of earth Oceanic Crust  Average thickness 7km thick and composed of igneous rock basalt and gabbro  Density- 3.0 g/cm3 Continental Crust  Average thickness 40 km thick ranges from 8-75 kilometers thick and composed of granite  Density- 2.7 g/cm3 2. Mantle Over 82% o f Earth’s volume is in the mantle The mantle is a rocky shell that extends to 2890 km The upper mantle is made of peridotite Density- 3.4 g/cm3 3. Core Sphere composed of an iron-nickel alloy Density- 13 g/cm3

4. Lithosphere Asthenosphere Outer Core Inner Core

5. Lithosphere- Earth’s outermost layer consisting of the crust and the uppermost mantle. Averages about 100 km in thickness Asthenosphere Lies beneath the lithosphere Soft, weak layer Has temperature/pressure conditions that result in a small amount of melting This makes this layer weak, yet not a complete liquid

6. Lower Mantle From about 660 km down to the base of the mantle is the rigid lower mantle Outer Core Liquid layer of metallic iron 2260 km thick Flow of metallic iron generates Earth’s magnetic field Inner Core Has a radius of 1220 km High temperature, but yet material remains solid- Why?

7. 1909 Croatian seismologist- Andrija Mohorovicic (MOE- HOE-ROE-vee-cheech) Studied seismic records and found that the velocity of seismic waves increases abruptly below the crust at about 50 km depth This boundary is called the Mohorovicic discontinuity or Moho for short Another boundary was discovered when it was observed that one type of Earthquake wave (P wave) bent through the liquid core of the Earth. This shows scientists that the core must be made out of a different material. Further testing showed that another type of wave (S wave) could not travel through the core at all, S waves cannot travel through liquids. This helped scientists conclude that the outer core was in fact a liquid.

8. Early seismic data and drilling indicated that the continental crust was composed of mostly granite, while the oceanic crust is composed of mostly basalt Lava eruptions give us a good idea of what is present in the mantle of the earth Meteorites are thought to be of similar substance as that of our Earth’s core (dense iron and nickel) The densest materials would sink to the center also evidence of what exists at the core of our Earth.