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Plate Tectonics The Plate Tectonic Theory • Earth’s lithosphere is broken into pieces called plates, and their movement creates major changes in Earth’s surface. At least 3 times in the past, most of the large landmasses have come together, forming supercontinents. Plate Boundaries Plate Boundaries Movement Divergent AWAY from each other Convergent TOWARDS each other Transform SIDEWAYS Arrows on Map Type: Divergent Plate Boundary Key Characteristics: New crust is made Example: Mid-Atlantic Ridge Type: Oceanic-Continental Convergent Key Characteristics: subduction, trenches, volcanoes, deep earthquakes Example: Peru-Chile Trench Mariana’s Trench = deepest point on Earth (35, feet deep) Aleutian Trench Type: Continental-Continental Convergent Key Characteristics: Mountain Building Example: Himalayas Type: Transform Fault Key Characteristics: • Slide past one another • Shallow Earthquakes Example: San Andreas Fault What DRIVES Plate Tectonics? • The current accepted theory about what makes the plates move: – CONVECTION CURRENTS in the mantle pushes plates apart or towards each other. Divergence Convergence Convergence Subduction Hot, ____________ dense material formed deep within Earth’s mantle rises. When this material cools near the surface, it becomes ______________dense and sinks. The resulting convective flow of this material in the mantle ___________________ lithospheric plates across the surface of the Earth. Hot Spots • Hot Spots: major regions of volcanic activity in the interior parts of plates • EX: Animation Kauai 4 my old Molokai Oahu 2.5 my old 1.5 my old Hawaii Maui 1.2 my old 0 my old Effects of Plate Tectonics 1. Appearance of Continents: the outlines of present-day continents appear to fit together like puzzle pieces. Effects of Plate Tectonics 2. Similar landmass features: minerals, rocks, fossils, age, and mountain ranges are found at places where continents have joined together in the past. The reptile Mesosaurus swam in the freshwaters of Pangaea 260 million years ago. Today, its fossils are only found in Africa and South America. Effects of Plate Tectonics 3. Age and Heat Patterns of Oceanic Rocks: as you move further away from a mid-ocean ridge, the crust gets older and cooler. Effects of Plate Tectonics 4. Magnetic Stripes: the ocean floor shows a pattern of magnetized “stripes”, recording reversals in Earth’s magnetic field. Video Clip Animation Paleomagnetism The Earth's magnetic field produces invisible lines of force that extend from one pole to the other. A compass needle aligns itself with these lines of force — points toward the magnetic poles. 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." demo