Chapter 7 Plate Tectonics

Unit essential questions How do we know that plates move? How is the Earth’s surface shape by plate motion? Why do earthquakes and volcanoes occur?

What is happening now S. America is moving away from Africa 2 to 3 cm/year Hawaii is moving northwest at rate of 8 to 9 cm/year Mt. Everest is slowly rising

Alfred Wegener A German scientist, geophysicist, and meteorologist in early 1900’s Continental drift = Earth’s continents had once been joined as a single landmass (Pangea), and slowly drifted away from one another, like gigantic puzzle pieces Analyzed rock type, geological structures and fossils at the “edges” of the puzzle pieces

Today Pangea puzzle piece activity Take notes on evidence that continents move (p. 218 – 220). Use the following table to organize your notes. You should have about 4 – 5 points per evidence. 3. Questions 1 – 8 on page 222 Climate clues Fossil clues Rock clues

Chapter 7.2 Development of a Theory

Continental drift

Evidence Rock Fossils Climate Appalachian mountains in US share similar rock in Greenland and Europe Land dwelling reptile Lystrosaurus and Cynognathus – weak swimmers, could not have swum large distances Mesosaurs (aquatic reptile) found only in fresh water so likely did not cross the ocean Glossopteris (fern) seeds could not have travelled far Glacial deposits in South America, Africa, India and Australia – this area was once near the south pole

A rejected hypothesis Many people did not believe Wegener that plates moved Why? Could not explain how it moved Could not explain what forces move continents Later accepted in the early 1960s, 30 years after his death

Seafloor spreading Process by which new oceanic crust forms along mid ocean ridge and older crust moves away from the ridge If the sea floor spreads, continents must be moving Determine the age of the rock across the sea floor Continents are “passengers “that ride with ocean crust as it slowly moves away from ocean ridges

7.3 The theory of plate tectonics Quiz on chapter 7 next class.

Seafloor spreading Process by which new oceanic crust forms along mid ocean ridge and older crust moves away from the ridge If the sea floor spreads, continents must be moving Determine the age of the rock across the sea floor Continents are “passengers “that ride with ocean crust as it slowly moves away from ocean ridges

Plate tectonics Earth’s surface is made of rigid slabs of rock, or plates, that move with respect to one another Lithosphere – Earth’s outermost layer Asthenosphere – plastic material beneath lithosphere

Why or how do continents move? Convection current = circulation of materials caused by differences in temperature and density Hot air rises while dense, cold air sinks

Plate Boundaries Divergent plate boundary = two plates separate Transform plate boundary = two plates slide past each other Convergent plate boundary = two plates collide Dense plate sinks below the more buoyant plate in a process known as subduction

Today Try the oreo cookies and plate tectonics. You do not need to answer the questions. On page 243, answer questions 13 – 23