Are Continents “Drifting”? YES Evidence - Earth’s highest point is rising (Mt Everest) America moving from Africa 2-3 cm/yr Hawai’i migrating 8-9 cm/yr

Continental Drift Who developed the theory? Alfred Wegener Meteorologist

Continental Drift What is Continental Drift? Earth’s continents were once connected into a supercontinent Pangaea It began to break up about 280 million years ago They continue to move

Continental Drift What are the early observations? What is the evidence? Matching coastlines (1500s) Puzzle-like fit of S America/Africa & Europe/N America

Continental Drift Distinctive rock type on widely scattered continents Distinctive geologic structures (mountains) What is the evidence?

Continental Drift Same land-dwelling plants and animals Mesosaurus Glossopteris Lystrosaurus What is the evidence?

Continental Drift What is the evidence? Coal deposits in Antarctica Glacial deposits in Africa, India, Australia & South America

Continental Drift Why rejected? Could not explain what caused the continents to move – “What force could be strong enough to move continents over such large distances?” Continents would fracture if pushed through the ocean floor

Plate Tectonics What is Plate Tectonic Theory? Earth’ crust and upper mantle is broken into large slabs called plates that move in different directions and at different rates over Earth’s surface

Plate Tectonics Sea Floor Spreading What is the evidence? First proposed by Harry Hess What is the evidence?

Plate Tectonics What is Sea Floor Spreading? The process by which new oceanic crust is formed by the upwelling of magma at mid-ocean ridges.

Plate Tectonics Evidence for Sea Floor Spreading? Mid-Ocean Ridges – huge underwater mountain chains Deep sea trenches – deep chasms

Plate Tectonics Evidence for Sea Floor Spreading? Age of rocks – youngest near ridges, oldest farther away Highest heat flow near ridges Elevation highest near ridges Ocean sediment thinnest near ridge

Plate Tectonics Evidence for Sea Floor Spreading? Symmetrical magnetic patterns on opposite sides of a ridge

Plate Tectonics Evidence for Plate Tectonics? Patterns of earthquakes and volcanoes Locations associated with plate boundaries

Causes of Plate Motion Causes Mantle convection Hot mantle rises, cool mantle sinks carrying the plate with it as it convects Convection – transfer of heat by moving fluids

Causes of Plate Motion Causes Ridge Push Uplifted ridge produces a slope the older, denser lithosphere slides down the slope away from the ridge toward the trench formed at a subduction zone

Causes of Plate Motion Causes Slab Pull Denser, heavier plate subducts beneath less dense plate pulls the rest of the plate with it, eventually dragging trailing plate into a subduction zone