Continental Drift

1. Continental Drift • Alfred Wegener thought of the theory of continental drift-that the continents move. • 250 million years ago all the continents were connected as only one continent called Pangaea. • His reasons were: • The same types of rock were on different continents • The shapes of the continents “fit together” • The same types of fossils were on different continents • 180 million years ago Pangaea broke in two pieces, Gondwanaland and Laurasia • Geologists think that convection currents in the mantle move large sections of the Earth’s crust, called plates. • The plates are still moving!

2. Boundaries • Plates move ___________________________ at transform boundaries. • Plates move ___________________________ at divergent boundaries. • Plates move ___________________________ at convergent boundaries. • Transform Boundaries • frequently cause ___________ • no new crust formed, __________ old crust recycled • moves about 2 in (5 cm) per year on average • example: ________________ • Divergent Boundaries • plates move _______________each other • examples: the Mid-___________ Ridge, Iceland, the African Rift Valley • lava forms new crust and __________ the older crust away. • underwater this is called sea-floor _____________ • the newest crust is _____________________ • most ______________ are at divergent boundaries

3. Boundaries p.2 • Convergent Boundaries • Plates move towards each other and ________ • Examples: Ring of Fire, Andes Mtns., Aleutian Islands, Himalayan Mtns. • many mountains, volcanoes and ___________ happen at convergent boundaries • old crust is ________ and recycled • Could be continent vs. continent • pushes up tall __________________ parallel to boundary, like Himalayan Mountains with Mt. Everest • Could be oceanic vs. (continent or oceanic) • oceanic plates are ___________ and heavier than continental plates • subduction occurs when the oceanic plate slides _______________ the other plate and melts in mantle. • forms a deep trench, example: _____________ Trench in Pacific Ocean or arcs of ____________________ that are parallel to boundary • makes lots of cracks in upper plate, which fill with ______________ making ___________________

4. Earthquakes • happen at faults (cracks in the crust), not just at transform boundaries • Faults are in tension (being pulled), until they move and vibrate • Seismic waves carry those energy from those vibrations in 3 directions • P waves go front to back, fastest speed • S waves go side to side • Surface waves go up and down, slowest speed • The focus is where the earthquake starts underground. • The epicenter is directly above the focus on the surface. • A seismometer is a device that prints a picture of the vibrations called a seismograph. • The magnitude (strength) of an earthquake is measured on the Richter scale. • NO ONE CAN PREDICT AN EARTHQUAKE!