1. Plate Tectonics Seafloor Spreading

2. Plate Tectonics 4 – Name the four main layers of the earth from inside to outer most layer. 3 – Name the three physical structures of the Earth. 2 – Identify the state of matter for the two parts of the core. 1 – Write one fact about the Earth’s layers you find interesting. When you are finished with Bellringer finish reading section 6.2 the rest of page 192 to page 195. Bellringer -Inner Core -Outer Core -Mantle -Crust L-Lithosphere A-Astenosphere M-Mesosphere Inner Core is SOLID Outer Core is HOT MOLTEN LIQUID I think it is interesting how the outer core spins around the inner core. What about you?

3. Plate Tectonics Mid-Ocean Ridges Mid-ocean ridge – undersea mountain chain where new ocean floor is produced –Discovered by using sonar (a device that bounces sound waves off underwater objects and then records the echoes) Harry Hess – (American) first geologists to study mid-ocean ridges –Found evidence to back up Wegener’s Continental Drift Theory –Called this seafloor spreading - Sea-Floor Spreading

4. Plate Tectonics Mid-Ocean Ridges The East Pacific Rise is just one of the many mid-ocean ridges that wind beneath Earth’s oceans. - Sea-Floor Spreading

5. Plate Tectonics What Is Sea-Floor Spreading? Sea-floor spreading – The sea floor spreads apart along both sides of a mid-ocean ridge as new crust is added –Ocean floors move like conveyor belts, carrying the continents along with them. - Sea-Floor Spreading

6. Plate Tectonics Evidence for Sea-Floor Spreading Hess found evidence to support his theory of sea- floor spreading, which included: –eruptions of molten material, magnetic stripes in the rock of the ocean floor, and the ages of the rocks themselves. - Sea-Floor Spreading

7. Plate Tectonics Evidence for Sea-Floor Spreading Evidence From Molten Material –1960’s – submarine Alvin found rocks along the ocean floor running parallel with the ridge –These type of rocks only form when molten material hardens quickly after erupting under water Evidence From Magnetic Stripes –rock that makes up the ocean floor lies in a pattern of magnetized “stripes.” –record of reversals in Earth’s magnetic field. - Sea-Floor Spreading

8. Plate Tectonics Evidence for Sea-Floor Spreading Evidence From Drilling Samples –Glomar Challenger – (1968) drilling ship that obtained rock samples from the ocean crust –Found that the rocks closest to the mid- ocean ridge were “younger.” –The farther away from a ridge the samples were taken, the older the rocks were

9. Plate Tectonics Subduction at Trenches Deep-ocean trench – deep valley along the ocean floor beneath which oceanic crust slowly sinks toward the mantle. –The oceanic crust bends downward into the mantle Subduction – process by which oceanic crust sinks beneath a deep-ocean trench and back into the mantle. –Occurs at a convergent plate boundary Trench Subduction

10. Plate Tectonics Subduction at Trenches In a process taking tens of millions of years, part of the ocean floor sinks back into the mantle through deep-ocean trenches. - Sea-Floor Spreading

11. Plate Tectonics Growing an Ocean Because of sea- floor spreading, the distance between Europe and North America is increasing by a few centimeters per year. - Sea-Floor Spreading

12. Plate Tectonics Complete 6.2 Review on the answer sheet provided to you. -Key Concepts: #’s 1-3 -Critical Thinking: #’s 4-5 -Challenge: # 6 YES YOU HAVE TO DO THE CHALLENGE!!!! Also, complete the reverse side of the answer sheet. Turn In!