Presentation on theme: "Continental Drift and Plate Tectonics"— Presentation transcript:
1Continental Drift and Plate Tectonics Birth of a TheoryContinental Drift and Plate Tectonics
2Wegener’s HypothesisAlfred Wegener proposed that all the continents were once joined together in a single super continent called Pangaea.He proposed that it began to break apart around 200 million years ago.This is the continental drift hypothesis
4Evidence for his theory Continental PuzzleFossil evidence of several organisms of the same species on different landmasses.( Glossopteris Fern, Mesosaurus Reptile)Rock types and structuresAnd climate evidence.
6Problems with his theory Couldn’t provide a mechanism for how the continents moved.
7A new TheoryPlate Tectonic theory- says the earth is made up of rigid plates that contain the crust and upper mantle also known as the lithosphere moving long the asthenosphere.Lithosphere- the crust and upper mantleAsthenosphere- Plastic like layer of mantle beneath the crust
8Plate BoundariesDivergent boundaries (also called spreading centers) are the place where two plates move apart.Convergent boundaries form where two plates move together.Transform fault boundaries are margins where two plates grind past each other without the production or destruction of the lithosphere.
10Evidence for Plate Tectonics Mid-Ocean ridges and rift valleys that cause sea floor spreading provided a mechanism for the plate tectonic theory.Seafloor spreading process that produces new oceanic lithosphere.subduction zone occurs when one oceanic plate is forced down into the mantle beneath a second plate.
13Convergent Plate Boundaries Oceanic-Continental-Continental volcanic arcs form in part by volcanic activity caused by the subduction of oceanic lithosphere beneath a continent.Examples include the Andes, Cascades, and the Sierra Nevadas
20FaultsNormal faults occur when the hanging wall block moves down relative to the footwall block.Reverse faults are faults in which the hanging wall block moves up relative to the footwall block.Reverse Thrust faults are reverse faults in which hanging wall moves up and over the footwall.Strike-slip faults are faults in which the movement is horizontal and parallel to the trend, or strike, of the fault surface.
22Earthquakesearthquake is the vibration of Earth produced by the rapid release of energyFocus is the point within Earth where the earthquake starts.Epicenter is the location on the surface directly above the focusFaults are fractures in Earth where movement has occurred
25Cause of EarthquakesMost earthquakes are produced by the rapid release of elastic energy stored in rock that has been subjected to great forces.When the strength of the rock is exceeded, it suddenly breaks, causing the vibrations of an earthquake.
27Earthquakes cont.An aftershock is a small earthquake that follows the main earthquake.A foreshock is a small earthquake that often precedes a major earthquake
28Earthquake WavesSeismographs are instruments that record earthquake waves.Seismograms are traces of amplified, electronically recorded ground motion made by seismographsSurface waves are seismic waves that travel along Earth’s outer layer.
31Earthquake Waves cont.P waves- push-pull waves that push (compress) and pull (expand) in the direction that the waves travel.Travel through solids, liquids, and gasesTravel the fastest
32Earthquake Waves Cont.S waves-Seismic waves that travel along Earth’s outer layer.Shake particles at right angles to the direction that they travel.Travel only through solidsSlower velocity than P waves
35Richter Scale Based on the amplitude of the largest seismic wave Each unit of Richter magnitude equates to roughly a 32-fold energy increaseDoes not estimate adequately the size of very large earthquakes
36Momentum MagnitudeDerived from the amount of displacement that occurs along the fault zoneMoment magnitude is the most widely used measurement for earthquakes because it is the only magnitude scale that estimates the energy released by earthquakesMeasures very large earthquakes
44Volcanic MaterialsPyroclastic materials is the name given to particles produced in volcanic eruptions.Types of pyroclastic materialAsh and Dust- very fine in sizedCinders- Pea SizedBombs- large sized
45Types of VolcanoesShield volcanoes are broad, gently sloping volcanoes built from fluid basaltic lavasCinder cones are small volcanoes built primarily of pyroclastic material ejected from a single vent.Composite cones are volcanoes composed of both lava flows and pyroclastic materialMost violent type of activity