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Structure of the Earth

Structure of the Earth. Earth’s Interior.

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Structure of the Earth

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  1. Structure of the Earth

  2. Earth’s Interior • What we know about Earth’s interior comes from indirect avenues of investigation. Earth’s diameter is approximately 12,756km (~ 7,500 miles). -the deepest hole we have ever drilled into the Earth is 9.6 km (~5 mi). so how do we know what it’s like?Seismic waves! - natural and man-made

  3. Earthquakes • seismic (energy) waves travel through the earth some energy bounces off harder layers called reflection some energy travels through but gets bent, changing the direction the wave is traveling called refractionsome energy is absorbedas it encounters materials

  4. Shallow high frequency seismic waves allow us to see reflectors and refractors at depth

  5. Wave paths in the Earth

  6. Factors affect seismic waves distance- farther = more attenuation density- higher = faster temperature- colder = faster liquid vs solid - solid = faster; p-waves and s-waves - liquid = slower; no s-waves angle of incidence- controls how much is reflected and how much is absorbed vertical arrangement of layers - controls the resultant direction of travel

  7. P-wave and S-wave shadow zones- caused by transmissive and refractive properties of the waves interacting with rocks

  8. Concentric spheres of material with distinctive characteristics make up each layer in the Earth

  9. Notice how the temperature changes as you travel deeper into the Earth.

  10. Crust- the rigid outer shell of the earth, composed of solid rock; very thin- averages only 20 km thick (the crust composes the Lithosphere) TWO KINDS OF CRUST: Oceanic- most abundant; consists of rocks formed from mafic magma; very dense; very thin- 10 km thick Continental- underlies continents; consists of rock formed from magma; less dense than oceanic crust; thick-30 to 75 km thick

  11. Model of Lithosphere and Aethenosphere showing thickness of Oceanic vs Continental crust Continental crust Oceanic crust Uppermost mantle- Aesthenosphere Mohorovicic Discontinuity“The Moho”

  12. Moho Discontinuity The boundary between the crust and the mantle is called the Mohorovicic discontinuity. Scientists know it exists because the speed of seismic waves changes after it goes deeper than the crust.

  13. The Mantle • Semi solid material (jello-like) underneath the crust that extends down about 3000 km (1850 miles) • Made up mostly of iron, nickel, and magnesium • Has convection currents that cause the molten material to move due to the temperature changes within the mantle

  14. Heated rising material Cooled sinking material

  15. 3D maps of the earth’s convection currents based on seismic wave analysis-complicated looking http://education.sdsc.edu/optiputer/flash/convection.htm

  16. Earth’s core Broken into an inner and outer zone Outer zone is liquid- doesn’t transmit s-waves Probably composed of Nickel (Ni) and Iron (Fe) along with some other elements (Sulfur or Nitrogen) Inner core is solid- based on speed of P-wave travel composed of same materials as outer core Important for generating Earth’s magnetic field

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