Continental Drift Alfred Wegener- 1912 -continents were at one time a huge landmass- PANGAEA- “all lands” About 200 mya began to break up and drift to present location Surrounding Pangaea huge ocean claaed PANTHELESSA- “all seas”

EVIDENCE OF CONTINENTAL DRIFT - Similarities in coastlines of continents - same Fossils found on eastern S. America and west Africa - Rock type and age of coastal regions -Glacial debris

SEA FLOOR SPREADING Mid ocean ridges- (65,000 km) under sea system of mountain ranges RENEWAL OF OCEAN FLOOR -Harry Hess- (1947) 1- if ocean floor pulls away from both sides of ridge, 2- it is replaced by rising magma (upwelling), 3- it is cooled and solidified into new rock (new ocean floor)

PLATE TECTONICS There are about 30 known lithospheric plates Describes continental movement How and why continents move

EARTH’S 2 CRUST TYPES - Continental crust- CONTINENTAL LANDMASS - Oceanic crust- OCEAN FLOOR more dense than continental - Along with the rigid upper mantle all three make up the thin outer shell called the LITHOSPHERE - Underneath the lithosphere is a layer of plastic rock that flows like putty under pressure called the ASTHENOSPHERE -plates float like wood (lithosphere) in water (asthenosphere)

3 LITHOSPHERIC BOUNDARIES DIVERGENT BOUNDARY- plates pull apart -Mid ocean ridges (MOR) separate narrow valley is formed called rift valley -molten rock rises to fill empty space after separation -mostly found on ocean floor hardens and cools to form new ocean floor

CONVERGENT BOUNDARY- direct collision of plates 3 TYPES OF COLLISIONS 1- oceanic crust to continental crust -b/c the more dense oceanic crust subducts under less dense continental crust - creates a SUBDUCTION ZONE where two crusts collide - this zone creates a deep ocean trench

2- continental crust to continental crust- -colliding edges of crust crumple and uplift creating mountains ex. Himalayas 3- oceanic crust to oceanic crust- -deep ocean trench forms when one is subducted under another - melting at subduction zone, molten rock rises along trench to form a chain of volcanic islands called an ISLAND ARC

TRANSFORM FAULT BOUNDARY Two plates grind past each other Move in sudden spurts EX. San Andreas Fault, CA

CAUSES OF PLATE MOTION Convection –transfer of heat through heated material As a material is heated it becomes less dense and rises, as it rises it cools and becomes more dense and sinks This is referred to as a CONVECTION CURRENT This occurs in the asthenosphere