Commotion Beneath the Ocean Introduction to Plate Tectonics Plate Tectonics Originally proposed by Wegener - but ridiculed !! 1960s new evidence found Earths Surface Continually Shifting Plate - Large, Rigid Slab of Solid Rock Tectonics- to build Theory of Continental Drift Pangaea 225 mya Earth/Solar System bya Life 3.4 bya Evidence of Continental Drift Coastline shapes Rocks Minerals Fossils Inside the Earth Crust Mantle Core Convection Heated material expands - becomes less dense - more buoyant It rises and cold material takes its place Heat Decay of Radioactive Elements inside Earth Trying to Escape Convection - transport of mass by heat (heat changes the density) Mid- Ocean Ridges Sonar Mapping Began during WWII By 1960s clear maps of mid ocean ridges Ocean Maps All the major oceans have long ridges Underwater Volcanoes Opening of the earth where hot molten rock, ash, and gases to escape from deep below the surface Underwater volcanoes are called Hydrothermal vents So what do the ridges have to do with plate movement? Undersea volcanoes Deposit molten rock from mantle convection Seafloor spreading - Supported Theory of Plate Tectonics Harry Hess Seafloor Spreading as proposed by Harry Hess New Ocean Floor deposited at the ridges Moves laterally away from the ridges Moves back down at the continental margin Continents are not islands they are parts of larger plates that move on the soft asthenosphere Earths Magnetic Field Liquid Iron in the outer core Moving Electrical charges (current) INDUCE a magnetic field Aligns approximately with the spin axis but periodically flips N S Evidence for Seafloor Spreading Magnetic Reversals Rocks have magnetic fields When rocks cool magnetic minerals align to Earths Mag Field 1960s drilling found Mirror images on each side of mid Atlantic ridge How old is the lithosphere? Dates of rock increased on both sides of mid-ocean ridges The Plates Earth - egg Shell - cracked, but stronger than the interior Tectonic plates - in the lithosphere Plates Tectonic plates are in the lithosphere The lithosphere floats on the Asthenosphere Asthenosphere is undergoing convection Plates are moving and interact with other plates Plate Boundaries Transform Divergent Convergent Divergent Plates Lithosphere is being produced Happens at mid ocean ridges Plate motion is away from the boundary Sea-floor spreading Well if two plates are diverging.. Convergent Boundaries Lithosphere sinks back into the asthenosphere (its recycled) One plate moves under another plate - SUBDUCTION The ocean plate is denser !! Continent - Continent When two continental crusts converge, the result is a huge mountain range. Both pieces of crust are buoyant. Example - Himalayas Indian plate -->> Asian plate. Numerous earthquakes but very little volcanism. Transform Plate Boundaries One plate slides parallel to another plate San Andreas Fault Plate boundary details for the West Coast of North America Divergent Plate Boundaries Hot Spots and Hawaiian Islands 1963 Tuzo Wilson (also discovered transform faults) Noticed Volcanism in some areas active for a really long time Heat produced magma, melted through the plates. Magma lighter than the rock rises. Hawaiian Chain Hot Spots Measuring Hot Spots Yellowstone Plate moves Hotspot does not Determine and compare the age of the rocks New evidence shows that hot spot may also move somewhat Hot Spots Yellowstone: several craters or calderas Energy fuels hot springs and geysers - Old Faithful May be a Super Volcano !! Review