1. Plate Tectonics Earth Science

2. Continental Drift Alfred Wegener proposed the idea of continental drift in 1912. Looking at the continents, it is possible to visualize that they all fit together. All the continents were together in one landmass called Pangaea. There are several different clues that suggest this might be true.

3. Clues Fossil Clues: Fossils from certain animals were found on several continents to suggest they were once together. Climate Clues: Warm weather plants have been found in the arctic where they would normally not grow. Rock Clues: Similar rock structures are found on different continents.

4. Continental Drift What could make the continents drift apart?

5. Seafloor Spreading Under the oceans, there are valleys and ridges throughout the world. Mid-ocean ridges form underwater mountain ranges Theory of seafloor spreading was introduced in the 1960s Magma is pushed up through a mid- ocean ridge and forces the seafloor to spread

6. Seafloor Moves Scientists found that the youngest rocks underwater were near the mid-ocean ridge and that there were no rocks older than 180 million years.

7. Magnetic Clues Earths magnetic field has reversed itself several times throughout history. Scientists measured the polarity of the rock in the ocean, and found that it did reverse itself.

8. Plate Tectonics This theory states that the Earth’s crust is broken up into sections. The sections are called plates and move around the mantle. Plates are made up of the crust and part of the upper mantle, together called the lithosphere.

9. Composition Lithosphere is rigid and about 100 km thick. This layer floats on top of the asthenosphere below it.

10. Plate Boundaries There are 12 different tectonic plates When plates interact they can… –Collide –Pull apart –Slide past each other

11. Boundary Types Divergent: 2 plates moving apart from one another Ex: Seafloor spreading Mid-Atlantic Ridge Great Rift Valley Convergent: 2 plates coming together 3 types In the collisions, one plate will slide underneath another creating a subduction zone

12. Convergent Boundaries Volcanoes usually occur in subduction zones. Type 1: Ocean & Continental plates –Ocean plate will slide beneath the continental plate. –Creates a deep-sea trench & forms volcanic mountains Type 2: Ocean- Ocean collision –Creates a deep sea trench and an island arc of volcanoes Type 3: 2 Continental Plate Collide –Usually no subduction –Mountains form –Earthquakes common

13. Transform Fault Occurs when 2 plates slide past each other. Earthquakes often occur Ex: San Andreas Fault

14. Causes of Plate Tectonics Convection currents – cycle of hot plasma rising and cooled plasma sinking causes the plates to move. –Hot plasma is less dense than cool plasma

15. Effects of Plate Tectonics Earthquakes Volcanoes Form several different landforms –Mountains –Faults –Rift Valleys

16. Landforms Mountains, Arcs, & Volcanoes: formed from converging plates. –Ocean/Ocean = arcs & volcanoes –Continental/Ocean = volcanoes –2 Continental = mountains Strike Slip Faults: when plates are sliding past each other. Faults & Rift Valleys: form as divergence occurs