Ch. 6 Plate Tectonics

6-1 Continental Drift Continental Drift theory that the continents were once a single land mass that broke apart Pangaea supercontinent

Evidence of Continental Drift South America & Africa look like they fit together Fossils of mesosaurus found in S. America & Africa

Evidence of Continental Drift cont. Mountains on different continents match U.S. & Canada match w/ Greenland & Europe Sizes of diamonds in Brazil & W. Africa match

2 types of crust Continental Oceanic 6-2 Seafloor Spreading Less dense More dense

Mid-ocean ridge underwater mt. chain in the oceans 6-2 cont. Mid-ocean ridge underwater mt. chain in the oceans Rift crack Rift valley flat area btw. ridges

New seafloor magma rises up through a rift 6-2 cont. New seafloor magma rises up through a rift Magma cools making new crust New crust pushes floor apart at ridges

6-3 Evidence of Seafloor Spreading Trench deep canyons in the ocean floor Most in the Pacific Ocean Old crust ends up in trenches Melts & becomes magma again

Subduction zone area where crust is forced down in trenches 6-3 cont. Subduction zone area where crust is forced down in trenches Youngest fossils = closest to rift valleys, ridges, & trenches

Tectonic plates the lithosphere broken into pieces 6-4 Plate Tectonics Tectonic plates the lithosphere broken into pieces 7 major plates & 8 minor plates Asthenosphere liquid part of the mantle

Theory of Plate Tectonics explains how & why plates (continents) move Lithosphere floats on asthenosphere

Convection current less dense warm rises & denser cool sinks 6-5 Plate Tectonics Convection current less dense warm rises & denser cool sinks 3 types of plate boundaries Convergent Divergent Transform

Transform 2 plates sliding past each other 6-5 cont. Transform 2 plates sliding past each other Cause earthquakes

Convergent 2 plates move toward each other 6-5 cont. Convergent 2 plates move toward each other Oceanic + continental = oceanic subducts under the continental Continental + continental = mountain

Divergent 2 plates move away from each other 6-5 cont. Divergent 2 plates move away from each other Cause rift valleys Cause seafloor spreading

6-6 Effects of Plate Tectonics Earthquakes plates slide past each other at a fault Mountains plates collide & buckle upward

Volcanoes oceanic plate dips down & magma collects 6-6 cont. Volcanoes oceanic plate dips down & magma collects Hot spots place where magma reaches the surface Islands plates move over hot spots & volcanoes build