1. Continental Drift Hypothesis – Wegner believed continents had once been joined, and over time they drifted apart Pangaea – the first super-continent Alfred Wegner 1912 Presented early fossil evidence No evidence to explain how or why continents moved Continental Drift Theory later developed into the theory of Plate Tectonics

2. Evidence supporting Continental Drift a)Continental Puzzle – continents fit together b)Matching Fossils - matching fossils (Mesosaurus) on cross ocean landmasses c)Mountain chains and rock type – (Appalachian) d)Ancient climates – (ice core data, scratched bedrock)

3. Plate Tectonics Theory Earth's outermost layer, the lithosphere, is broken into 7 large, rigid pieces called plates : the African, North American, South American, Eurasian, Australian, Antarctic, and Pacific plates. Several minor plates also exist, including the Arabian, Nazca, and Philippines plates. plates are moving ~ 5 cm per year in different directions and speeds The place where the two plates meet is called a plate boundary Plates are crust and upper mantle

4. Plate Boundaries and Actions Seafloor spreading produces new lithosphere San Andreas Fault is an example of a Transform Fault East African Rift Valley is an example of a divergent plate boundary Himalayas are an example of convergent continental/continental plates

5. Evidence and Testing for Plate Tectonics Paleomagnetism – changing patterns of magnetized rocks Earthquake patterns – link between plate boundaries and earthquakes Ocean Drilling - age of seafloor sediment – Newest (ridge crests) – Oldest (continental edges) Hot Spots – show plates move over Earth’s surface (Hawaii)

6. Cause of Plate Motion (tectonics) Heat convection in the mantle is the basic cause of plate movement Slab Pull and Ridge Push – downward convective flow of lithosphere (plate boundaries) Mantle Plumes – upward convective flow (volcanoes, hot-spots)