1. Bell-Ringer  In your group, use the paper, marker, and anything else within the room to model a divergent boundary.

2. Early Evidence of Continental Drift  1620 –Sir Francis Bacon noticed that continent coasts fit like puzzle pieces --geological formations/ fossils match up across Atlantic ocean  1912, Wegner’s hypothesis of continental drift and “supercontinent” called Pangaea (didn’t explain HOW continents moved)  1950-60’s: Theory of Plate Tectonics

3. Pangaea

4. Sonar  After World War II, scientists used sonar to survey large areas of the sea floor. Using sonar, they discovered……. Sends a signal (sound) toward the ocean floor and analyzes the return signal (echo) that bounces off the sea floor or another submarine structure http://www.wern.com/id12.html

5. Plate boundary 1: Divergent or Mid-Ocean Ridge  Continuous chain of submarine volcanic mountains that circles the globe  Mid-ocean ridge system is largest geological feature on earth

6. Some of the earth’s major mid-ocean ridges

7. New sea floor is created at Mid Ocean Ridges  Rifts are cracks in the earth’s crust  Created at MOR, where pieces of oceanic crust separate  When a rift occurs, pressure from the mantle underneath the rift is released  Pressure release causes magma to push upward through the rift  Magma cools & solidifies  new sea floor!

8. Sea Floor Spreading  Process in which the sea floor moves away from a MOR as magma pushes it outward, and new sea floor is created

9. Magnetism  Earth’s magnetic field reverses direction about every 700,000 years  Cause related to movements of magnetic particles in earth’s molten (liquified) outer core  Many rocks contain tiny magnetic particles  Particles can move when rock is molten  Rocks are molten at MORs  Particles are frozen in place when rock cools

10. Magnetism (continued)  Even when earth’s magnetic field reverses direction, the rocks stay in place  Results in magnetic “bands” in the sea floor, running parallel to MOR  Bands alternate between “normal” and reverse magnetization  Allows scientists to determine orientation of earth’s magnetic field when the rocks cooled  Further supports sea floor spreading idea

12. Plate Boundary 2: Convergent or Trenches  If new sea floor is created, old sea floor has to be destroyed somewhere else  Old lithosphere destroyed at trenches  Two plates collide, one plate dips below other into mantle (subduction)  Plate breaks up & melts in the molten mantle  Breaking up causes earthquakes  Melting causes volcanoes

13. Continued…  When a continental plate collides w/ oceanic plate, the oceanic plate ALWAYS subducts  Why?  Continental crust is less dense than oceanic crust and sits up higher  Causes the development of continental volcanoes ANDES

14. Cont’d…  When two oceanic plates collide, one plate subducts -casues earthquakes & volcanoes  When two continental plates collide (only occurs on occasion)…  because both have a low density, neither tends to subduct  Instead, plates get “welded together” or cause buckling and fold like an accordion  Forms mountain ranges (Example: Himalayas formed when India collided with Asia)

15. Plate boundary 3: Shear boundary or transform boundary  Plates slide past each other  Neither creates nor destroys lithosphere  Builds friction that eventually “gives,” causing an earthquake  Ex: San Andreas Fault

16. Hydrothermal Vents  Seawater seeps into cracks in floor near the rift at mid-ocean ridges  heated by underlying mantle  Forces back up through crust at 50-68°F, sometimes 660°F

17. Hydrothermal Vents  Seawater seeps into cracks in floor near trenches and the rift at mid-ocean ridges  heated by underlying mantle  Forces back up through crust at 50-68°F, sometimes 660°F

18. Hydrothermal vents cont’d…  Water that’s seeped into cracks mixes with minerals (sulfides)  This hot water then emerges from the vent and solidifies when it meets the cold ocean water surrounding the vent  The minerals solidify too, forming mineral deposits, which form structures near the vent

19. Black smokers  A type of mineral deposit found at hydrothermal vents  Chimney-like structures  “smoke”= dense cloud of mineral particles  Largest black smoker = 200 ft above sea floor