Earth Science Pearson Physical Science Book Plate Tectonics Ch. 22 Section 4 Notes 1

Continental Drift Alfred Wegener (1912) Alfred Wegener (1912) German scientist German scientist All continents were once in one super continent called Pangaea All continents were once in one super continent called Pangaea During the Mesozoic Era, began to break up During the Mesozoic Era, began to break up Wegener died before he found the reason for continental drift Wegener died before he found the reason for continental drift

Evidence of Continental Drift Similarities in coastlines Similarities in coastlines Fossils of the same plants and animals are found on different continents Fossils of the same plants and animals are found on different continents Geological evidence begins on one continent and ends on another Geological evidence begins on one continent and ends on another Climate patterns Climate patterns Coal deposits found in cold regions Coal deposits found in cold regions Evidence of glaciers can be found in tropical areas Evidence of glaciers can be found in tropical areas

Final Evidence Seafloor Spreading Seafloor Spreading In 1947, scientist mapped the Mid- Atlantic Ridge In 1947, scientist mapped the Mid- Atlantic Ridge Found rocks closest to the ridge were younger than the rocks closer to the continents Found rocks closest to the ridge were younger than the rocks closer to the continents

Paleomagnetism Evidence for Seafloor Spreading Evidence for Seafloor Spreading Found there are bands of rocks on the ocean floor that have alternating polarities Found there are bands of rocks on the ocean floor that have alternating polarities Normal = minerals pointing north Normal = minerals pointing north Reverse = minerals pointing south Reverse = minerals pointing south Earth’s magnetic field has reversed itself many times in earth’s history Earth’s magnetic field has reversed itself many times in earth’s history

Paleomagnetism

Theory of Plate Tectonics Earth’s Crust: Earth’s Crust: Oceanic Oceanic Continental Continental Together with the rigid upper mantle make the lithosphere Together with the rigid upper mantle make the lithosphere broken into plates that are carried like blocks of wood on water broken into plates that are carried like blocks of wood on water Float on top of the asthenosphere (like putty) Float on top of the asthenosphere (like putty)

Lithospheric Plate Boundaries Divergent Boundaries Divergent Boundaries Two plates moving away from each other Two plates moving away from each other Molten rock fills in the crack that is formed Molten rock fills in the crack that is formed Most are found on oceanic boundaries Most are found on oceanic boundaries Ex: Mid-Atlantic Ridge Ex: Mid-Atlantic Ridge Convergent Boundaries Convergent Boundaries Two plates moving toward each other Two plates moving toward each other

Convergent Boundaries Oceanic and continental crust Oceanic and continental crust Oceanic crust is denser and subducted (forced under the other) Oceanic crust is denser and subducted (forced under the other) Creates a subduction zone, where the oceanic crust is pushed under the continental crust Creates a subduction zone, where the oceanic crust is pushed under the continental crust Also creates a deep ocean trench Also creates a deep ocean trench Water seeps into the mantle and melts the mantle; creates magma and volcanic eruptions Water seeps into the mantle and melts the mantle; creates magma and volcanic eruptions

Convergent Boundaries Continental and continental crust Continental and continental crust Both are pushed upward Both are pushed upward Produces large mountains like the Himalayas Produces large mountains like the Himalayas Oceanic and oceanic crust Oceanic and oceanic crust One plate is subducted, creates a deep ocean trench One plate is subducted, creates a deep ocean trench Magma is made and a volcanic island is created Magma is made and a volcanic island is created Called an island arc Called an island arc

Transform Boundary Two plates grind past one another horizontally Two plates grind past one another horizontally Sudden spurts of movement Sudden spurts of movement Ex: San Andreas Fault in California Ex: San Andreas Fault in California

Causes of Plate Motion Convection: transfer of heat through movement of heated material Convection: transfer of heat through movement of heated material Hot material rises; Cold material sinks Hot material rises; Cold material sinks Creates a convection current Creates a convection current Believe there are convection currents in the asthenosphere Believe there are convection currents in the asthenosphere As the plates move apart, upwellings from deep in the mantle replace the hard lithosphere As the plates move apart, upwellings from deep in the mantle replace the hard lithosphere As the lithosphere becomes older, colder and denser, it begins to sink back into the mantle As the lithosphere becomes older, colder and denser, it begins to sink back into the mantle