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Earth Science: Plate Tectonics

Earth Science: Plate Tectonics. How do we see inside the Earth?. Waves Seismic waves Seismology Study & measurement of seismic waves What do we know that produces seismic waves?. Two main types of waves. “P” Waves “S” waves. P-waves. “P” or Primary waves Longitudinal

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Earth Science: Plate Tectonics

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  1. Earth Science: Plate Tectonics

  2. How do we see inside the Earth? • Waves • Seismic waves • Seismology • Study & measurement of seismic waves • What do we know that produces seismic waves?

  3. Two main types of waves • “P” Waves • “S” waves

  4. P-waves “P” or Primary waves • Longitudinal • Compress and expand • Fastest • Travel through all mediums ( solid, liquid and air)

  5. “S” Waves • “S” or Secondary waves • Transverse • Vibrate up and down / side to side • Slower than “P” waves • Only travel through solids

  6. Layers of the Earth

  7. The Crust • Surface layer • Like an eggshell • Thin • Brittle • Can crack • Two regions: • Oceanic (Basalt rock) • Continental (granite rock) • Crust is less dense than the mantle • Like ice on water; the crust floats on the mantle

  8. The Mantle

  9. The Mantle • Rocky • Like the crust • Silicon • Oxygen • Iron, magnesium, calcium are heavier elements • Mantle is denser • How does the Earth’s crust add to the density of the mantle? • Weight bearing down on the mantle…it compresses the minerals, increasing the pressure and squeezing them into rocks.

  10. The Mantle • Higher temperature • Why? • Increased pressure • Decay of radioactive elements

  11. Layers of The Mantle • Upper mantle • Lithosphere • Rigid rock upper portion of upper mantle • Asthenosphere • Lies beneath lithosphere and “flows” like plastic • It is solid…silly putty • Lower mantle

  12. The Core • Two layers: inner and outer core • 15% Earth’s volume • 30% Earth’s mass • 2x as dense as the Earth’s mantle • Why? • Made of metallic iron • Inner core is VERY hot! • Some places as hot as the surface of the sun!

  13. The Inner Core • Solid Iron • How? • Pressure from Earth keeps Iron packed tightly; doesn’t allow it’s atoms to flow

  14. The Outer Core • Outer Core • Liquid Iron • Less pressure • Flows and spins as Earth rotates • Creates convection currents • Affects Earth’s surface • Produces electrical charge • Possibly responsible for Earth’s magnetic field

  15. Magnetosphere

  16. Convection Currents • What are convection currents? • Current of heat flows from core to crust • This sets up a convection current in the mantle

  17. Effects of Convection Currents • When the current comes at a weaker part of the crust, for example at a volcano, magma comes above the earth's surface. • This is called plate tectonics. • The movement of these plates goes very slowly. • The bumping of two tectonic plates causes an earthquake. • The convection current along the bottom of the crust causes the moving of the tectonic plates.

  18. Continental Drift & Tectonic Plates • Wegner’s Hypothesis on Continental Drift • The World’s continents are in motion • At one time, the continents were joined together as one… • This was known as Pangea • They fit together like a jigsaw puzzle

  19. What caused the continents to separate?

  20. Continental Drift • Wegner’s theory that proposed the landmass known as Pangea started breaking up • Separated into two parts: Laurasia and Gondwanaland • Wegner’s theory of the separation of Pangea was supported by fossil, biological, climatological and geological evidence

  21. Seafloor Spreading • Seafloor is not permanent • Constantly renewing itself • Mid Atlantic Ridge (longest & tallest mountain range in the world, center of the Atlantic Ocean) • Forms islands: Iceland and Azore • There are rifts in the mountains

  22. Plate tectonics • Continents move because they are embedded in plates • The plates shuffle or move atop of the Earth’s surface • Plates move in different directions and different speeds from each other • There are nine large plates and several smaller plates

  23. Plate Boundaries • Divergent Boundaries • Plates move away from each other • Comes from rock in athenosphere • Partially melted • The rock partially melts = lava • It was magma before it left the surface of the Earth

  24. Convergent boundaries • Plates move toward each other

  25. Transform fault boundaries • Plates slide past each other

  26. Earthquakes • Devastating • Stress (force) applied to rock • Stress causes strain • Eventually the rock cannot bend anymore • It breaks and releases stored energy • The released energy ( Seismic Waves) travel out in all directions

  27. Earthquakes cont • The initiating site of the seismic wave: focus • The point at Earth’s surface directly above the focus: epicenter • Measured on a Richter Scale ( the incraments are ten fold in magnitude…

  28. Tsunami • Seismic sea wave • Created by an earthquake

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