Ch 10 Plate Tectonics A Moonenland Production A subsidiary of Moonco. Inc

Continental Drift  Alfred Wegener (1912) German Meteorologist Continents moved slowly to their current locations. Pangaea- the single landmass of Earth that broke apart about 200mya. “All Land”

 Evidence  Puzzle-like Fit Coastlines of continents fit together like puzzle pieces. Examples: S.America & Africa

 Fossil Clues Certain fossils of ancient animals & plants are found on distant landmasses.  Freshwater/land-dwelling reptile Mesosaurus fossils have been found on South America & Africa.

 Fossils of the ancient plant Glossopteris were found in Africa, South America, Australia, India, & Antarctica.

 Climate Clues -Fossils of warm climate plants were found in present-day cold climates. (Coal) -Rocks deposited by glaciers from the ice ages have been found in present-day warm climates.

 Rock Clues Similar rock structures are found on different continents separated by oceans. -Appalachian mountains of the USA are similar to mountains found in Greenland & western Europe -Rocks of South America match those in Africa

Main objection to Wegener’s hypothesis was its inability to provide a mechanism for the movement of the continents.

Seafloor Spreading  Hypothesis Radio waves were used to map the ocean floor. Mid-ocean Ridges- underwater mtn ranges

Less dense magma flows sideways dragging the seafloor along. As the seafloor spread apart, magma flows up through cracks in at the ridge forming new rock.

Rift Valley Midocean Ridge

 Evidence Drilling – Ocean floor rock samples show that the age of the rock gets older the further the rock is from the mid-ocean ridge

 Magnetism – Changes in the magnetic alignment of the Earth are found in alternating bands in the seafloor rock.

Theory of Plate Tectonics  Theory Combined theory of Continental Drift & Seafloor Spreading. Earth’s crust & upper mantle (lithosphere) are broken into plates and move around on a plastic-like layer of the mantle (asthenosphere.)

Seven major plates: Pacific (largest) N. American S. American African Eurasian Australian Antarctic

 Plate Boundaries Divergent Boundaries –Two plates spread apart. –Where seafloor spreading occurs. –New crust is formed. Ex: Mid-Atlantic Ridge

Convergent Boundaries –Two plates come together (collide) –Oceanic plate will sink under a continental plate (subduction) producing a deep trench. Ex: Andes & Cascades

– Two oceanic plates will converge resulting in a volcanic island arc. Ex: Mariana Islands

– Two continental plates will converge & crumple forming folded mountains. Ex: Himalayas, Appalachians, & Alps

Transform Fault Boundary – Two plates slide past each other. – Move at different rates. – Also known as strike-slip faults. Ex: San Andreas Fault

 Causes (Hypothesis) Convection Currents –Hot magma rises in the mantle. –Magma hits the crust & cools. –Cooling magma sinks dragging the lithospheric plate with it (centimeters.) –Magma sinks into the mantle & reheats.

 Features Formed by Tectonics Faults – Cracks in the tectonic plates caused by stress. – Plate boundaries are also faults. – Movement along faults cause earthquakes.

Volcanoes Magma produced by friction during subduction oozes up through the crust, erupts, & forms volcanoes.

 Mountains Convergent & Divergent boundaries form mountains. Process of mountain building is called orogenesis. -Volcanic Mountains

Folded Mountains o Horizontal rock layers are squeezed from opposite sides, causing them to buckle & fold.EX: Himalayans & Appalachians

 Fault-block Mountains: Huge, tilted blocks of rock that are separated by faults.EX: Sierra Nevada

Upwarped Mountains- blocks of Earth’s crust are pushed up by forces inside the Earth. (Domes) EX: Rocky Mountains