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THE THEORY OF PLATE TECTONICS Did you know… Most people know that Earth is moving around the Sun and that it is constantly spinning. But did YOU know that the continents and oceans are moving across the surface of the planet? Volcanoes and earthquakes as well as mountain ranges and islands all are results of this movement. Why is this? Did you know… Most of these changes in the earth’s surface takes place so slowly that they are not immediately noticeable to the human eye. The idea that the earth’s landmasses have broken apart, rejoined, and moved to other parts of the globe forms part of the plate tectonic theory. Alfred Wegner “Father of Continental drift”. In 1912 he theorized that 200 million years ago ALL the continents were connected together as one large landmass called Pangaea. Wegener's theory had a problem!!!! His theory did not include a mechanism that could move the continental masses. Today evidence from geology supports the idea. THEORY OF CONTINENTAL DRIFT Just a little Humor So what are some of the evidences The Continental Puzzle Matching Fossils (plants and Animals) Rock Types and Structures Ancient Climates Paleomagnetism Continents Continents fit together Especially if you consider the entire continental plate EX: Africa & South America Puzzle Pieces Evidence: Fossil Record Some fossils are only found in certain places that are across an ocean from each other. EX: Mesosaurus - Found only in S.America and Africa How did they get there? Rock Types Some rock types and structures seem to end on one continent and pick up on another Ex: Appalachians stop at New Foundland & pick up in British Isles. Mountains Match Up! Evidence: Glaciers 220-300 million years ago ice sheets covered S. Hemisphere including Africa, S. America, Australia, and India Striations indicate that the ice sheet crossed the equator several times! Glaciers in AFRICA!!! Paleomagnetism When igneous rocks containing magnetic minerals crystallize, the crystals align themselves with the Earth's magnetic field. The magnetic field of the rock then points toward the magnetic pole that existed when the rock formed. If the rock is moved, its magnetic field will act as a"fossil compass." Paleomagnetism Magnetized minerals can be used to determine the latitude of their origin. PLATE BOUNDARIES The Seven Major Plates *Memorize these!!! The Pacific Plate The Eurasian Plate The North American Plate The South American Plate The African Plate The Antarctic Plate The Indo-Australian Plate Plate Boundaries Plate Boundaires To determine the location of a plate boundary scientists plot the worldwide distribution of earthquakes. This activity is located at mid- ocean ridges and subduction zones. As mentioned earlier, tectonic plates are always moving. pulling away from each other crashing head-on or sliding past each other. Depending on which way these plates are moving will decide what is happening on the earth you and I are standing on. Plate Tectonics But this doesn’t actually tell me how the mountains or volcanoes were formed or how earthquakes happen, or does it? Types of Plate Boundaries Transform Fault- slide past each other Divergent- pull apart Convergent- collide Divergent Plate Boundaries New crust is made as the plates pull away from each other. Also known as Seafloor spreading Site of many earthquakes Divergent Boundaries Find a divergent boundary on your map. Can you find the Mid-Atlantic Ridge? They’re Pulling Apart! When plates pull away from one another they form a diverging plate boundary, or spreading zone. Thingvellir, the spreading zone in Iceland between the North American (left side) and Eurasian (right side) tectonic plates. January 2003. Transform Fault Crust is neither produced nor destroyed as the plates slide horizontally past each other. Transform Fault Can you find a Transform Fault on your map? San Andreas Fault Now does it make sense why there are so many Earthquakes in California Convergent Boundaries Crust is destroyed as one plate dives under another. Three types: Oceanic- Continental Oceanic-Oceanic Continental- Continental Subduction Zones Subduction – one oceanic plate subducts (dives) beneath the other Oceanic-Continental Collision Oceanic lithosphere always subducts beneath continental lithosphere due to differences in density. Continental volcanic arc formed as the melting continent provides magma for the volcano. Example: Andes mountains animation Oceanic-Continental Collision Oceanic-Continental Collision Oceanic- Oceanic Collision Two ocean slabs collide One plate subducts and melts, the melted rock becomes an island volcano. This creates an Island Arc System forming volcanic islands in the middle of the ocean. Example: Japan animation Oceanic-Oceanic Collision Continental-Continental Collision Two continental plates collide This creates a Continental Arc System. They Crash! When both are continental plates, the plates push against each other, creating mountain ranges. Continental-Continental Collision So how did the Rocky Mountains form? Ancient plates hitting one another or the result of pressure on the North American Plate. Can you think of any other Mountain Ranges that may have formed this way. (Hint: Here in NC) A contemporary example The Indian Plate has been colliding with the Eurasian Plate for the past 40 million years and has uplifted and continues to uplift the Himalayas and the Tibetan Plateau. Why do tectonic plates move? So what about Hawaii?? Geologists believe that a huge column of upwelling lava, known as a “plume,” lies at a fixed position under the Pacific Plate. As the ocean floor moves over this “hot spot” at about five inches a year, the upwelling lava creates a steady succession of new volcanoes that migrate along with the plate - a veritable conveyor belt of volcanic islands. Hot Spots Other hot spots? Yellowstone Iceland Our Future
