TECTONIC PLATES.

TECTONIC PLATES.

1. WENEGERS THEORY.

   • Continental Drift.
     • Theory accepted in 1960.
       • Theory.
         • Discovered that the continental shelfs fitted together exactly.
         • Also found that mountain ranges had rocks of same age and identical fossil evidence in both continents.
         • In 1912 he proposed his hypothesis of continental drift, that were that all the continents were joined as one large supercontinent called pangea.
         • He wrongly believed that the continents were made up of a light crust that could slide over the ocean floor, as it was a continuous and denser layer.
       • Evidence.
         • Found evidence to prove that continents were once joined together. But dont find evidence to explain the movement of the continents and his theory was rejected. finally the theory was accepted.
         • 1-Geological evidence 2-Palaeontoligical evidence 3-Palaeoclimatic evidence
         • 1- Found that continental shelves fitted together. He also found identical rocks and geological structures on both sides of the continent.
         • 2- He found identical fossils of land organisms.
         • 3- It is suspected that the northen part of pangea was covered in large tropical rain forest, while the southern hemisphere was covered in glaciers.

2. STRUCTURE ANDCOMPOSITION OF THE EARTH.

   • Methods for studyng the Earths interior.
     • Core sampling and mining.
       • With current tecnology, the deepest they can drill is 13km, an insignificalt distance compare with the earths 6371km radious. Is not a efficent method.
     • Studying rocks.
       • There are natural phenomena which move rocks to the interior of the earth to the surface. Include erosion and volcanic eruptions.
     • Seismic methods.
       • The most important methods. Measures the seismic waves produced by earthquakes or controlled explosions. These waves travel through Earths interior. There are to tipes of waves: P and S.
       • P waves.
         • - First to arrive the surafce. - Faster. - Faster in solid than liquids. - Make terrestial particles move in same direction as wave.
       • S waves.
         • - Arrive after P waves. -Slower. -Travel to solids not liquids. - Make terrestial particles move perpendiculary to the wave.
     • Studying meteorites and asteroids.
       • Are fragments from when the solar system was created.
   • The composition and dynamics of the earth.
     • Compositional layers.
       • These are the crust, mantle and core.
       • Moho discontinuity separates the crust and the mantle. Gutenverg discontinuity separates the mantle and the outer core.
     • Physical layers.
       • The lithosphere is solid and rigid surface broken into pieces called plates. Asthenorphere and mesosphere are under the lithosphere, are solid but more flexible than ithosphere. Endosphere consist of the core, mainly liquid and inner core is solid.

3. PLATE TECTONICS.

   • Birth of plate tectonics.
     • Distribution of earthquakes and volcanoes.
       • Vibrations recorded by the seismographs were mapped and compared to the location of volcanoes. The maps showed that the earthquakes are distributed in thin lines called seismic belts, and are abundant in areas were volcanoes are found.
       • The scientists could see that there was a relationship between location of seismic and volcanic activity and the position of ocean trenches and ridges.
     • Sea-floor spreading.
       • drilling surveis not only showed that the ocean floor contains many volcanoes, also show that the age of the lava flows varies depending on the position relative to the ridge.
       • Sea-floor spreading is when the magma rises up and as the new lava moves up, it pushes the older lava deposits.
     • Subduction of ocean floor.
       • Subduction is the process in which the oceanic lithosphere moves under the continental lithosphere and into de mantle.
     • Tectonic plates.
       • Also known as the lithospheric plate, is a fragment of the lithosphere. Each plate separated by a seismic belt and volcanoes.
       • Depends on
         • Size.
           • Are 8 large plates and many small called microplates.
         • Type of lithosphere.
           • Are oceanic plates, continental plates and mixed plates.
   • Theory of plate tectonics.
     • Theory.
       • Volcanoes and earthquakes are in the bourders.
       • Plates.
       • Ocean floor formed.
       • Plates move continents.
       • Distribution of seismic and volcanic activity.
       • Formation and destruction of ocean floor.
       • Present and previous distrinution.
       • Formation of mountain ranges.
       • Distribution of minerals and fssil fuels.
     • How do plates move?
       • Original explanation.
         • Was accepted that the lithosphere 'floats' on the asthenosphere. Was throught the convection currents
         • hot currents- rise and separate. Ridges are formed cold currents- cool and descend. Trenches are formed.
       • Current explanation.
         • By seismic tomography.
           • lithospheric plates not only float, it also contribute to their own movement in two ways:
           • 1-the force of gravity pull down both sides of the plate.
           • 2- once is being subducted the weight of the plate pulls it down lower. Sinks down to the edge of the core.

4. OCEAN FLOOR,

   • Oceanic landforms.
     • Ocean trenches.
       • Deep channels, usually found next to continental boundaries or island arcs.
     • Seamounts and guyots.
       • Volcanic landforms. Seamounts have pointed tops and guyots have flat tops.
     • Island arcs.
       • Curved chain of volcanic islands, next to ocean trenches.
     • Abyssal plain.
       • A large flat area on the ocean floor.
     • Ocean ridges.
       • Very long underwater mountain ranges.
     • Rifts.
       • Big faults in ocean ridges.
     • Volcanic archipielagos.
       • Chain of volcanics islands next to hot spots.
   • Composition of the ocean floor.
     • Made up of volcanic rocks.
       • Volcanic rock has pillow- shaped formations, called pillow lavas, and magnetic rocks.
       • Very young rocks.
         • There are no older rocks from 180 million years. Closer rocks were younger than those further away from the ridge.

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