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Transcript
PLATE TECTONIC PUZZLE 1. 2. 3. 4. Reconstruct Pangaea What evidence led to your conclusion? What landmasses logically fit together? What other evidence led you to believe the continents fit together? Early Earth and Plate Tectonics The early Earth & Plate Tectonics The Earth’s Drifting Continents German scientist Alfred Wegener, 1900’s proposed the Theory of Continental Drift… he was not the only one to do this… he was able to collect evidence though Evidence 1. Glossopteris (gymnosperm… seed fern), located in 250 myo rocks, were found in South Africa, Australia, India, and Antarctica 2. Antarctica once had a warmer climate 3. Rock formations and deposits lined up on several continents 4. Evidence of glaciers in now warm climates The Evidence Same fossils on different continents Same species of plants and rock formations on different continents The Real Issue……….. How could the continents move through the solid rock bottoms of the oceans? In the 1950’s, scientists using better instruments found underwater mountain chains with rift valleys in their centers Midocean ridge Earth’s Spreading Ocean Floor A. Mid-ocean ridges form the single largest mountain range in the world (under the oceans) B. 80,000 km long and 3 km high C. Lava erupts to form new sea floor D. As it spreads it takes continents with it This explained the mechanism for continental drift! Seafloor Spreading Iceland, "the land of fire and ice", is being split by an oceanic ridge that surfaces to create an oceanic island in the North Atlantic Ocean. Interesting Iceland 1. 2. Slightly smaller than Kentucky 3. Natural hazards: Earthquakes and volcanic activity; avalanches 4. Environment issues: Water pollution from fertilizer runoff; inadequate wastewater treatment 5. More land covered by glaciers than in all of continental Europe 6. Number of volcanoes: 43 Average temperature is 11°C (52°F) in July and -1°C (30°F) in January Magnetic stripes on the ocean floor were further evidence that the sea floor was spreading. The patterns are identical on each side of the ridge Closer examination shows that the magnetic poles have reversed themselves anywhere from 9-2,000 times in the past 3.5 million years… depends on the strength of the field tested. Pole Reversal The magnetic pole is currently 966 kilometers (600 miles) from the geographic one. The magnetic pole lies in the Arctic Ocean… it is currently migrating toward Siberia Earths Magnetic Field LITHOSPHERIC PLATES Thousands protest against Global Warming!!! If the ocean floor is being created, is the Earth getting bigger?... No • Rock in the ocean is relatively young • Ocean floor is being destroyed in trenches in a process called subduction • The denser ocean crust is pushed downward into the mantle and melts • It is a cycle… some goes down and some goes up Some goes down Some comes up The Earth’s Moving Plates The Theory of Plate Tectonics, which links continental drift and seafloor spreading, explains how the Earth has evolved over time. It helps to explain the formation, movement, collisions, and destruction of the Earth’s crust PLATE TECTONICS Lithospheric Plates There are seven major plates, Pacific, North American, South American, Eurasian, African, Indo-Australian, and Antarctic There are many small plates, Caribbean, Arabian are examples Each plate moves at a different speed and direction Some are oceanic and some are continental ACTIVITY 1. Label & color the seven major plates 2. Answer the questions on the back Sand Art… Relax while you work Moody Slide… hopefully it will work Will the Earth Continue to Change? The Floating Crust Isostasy is the balance between the downward force of the crust and the upward force of the mantle Plate Boundaries Divergent boundary- plates moving apart C to C forms a rift valley that fills in w/ seawater: Iceland or African Rift Valley O to O forms a mid-ocean ridge: Mid-Atlantic Ridge Convergent boundaryplates that are moving together Collision of Continental and Oceanic Plates = Trench and Volcanic Arc Pacific Coast, Washington State Collision of 2 Continental Plates = Mountain Range Himalayas (India) Collision of 2 Oceanic Plates = Trench and Island Arc Transform boundary, slip-strike, lateral faults- plates slide past one another resulting in earthquakes San Andreas Fault is this type… and no CA will not fall into the ocean…. LA will be a suburb of San Francisco Plate Motion The power of the convection currents in the mantle is thought to be the force that moves the plates The Earth’s Changing Surface Stress is what causes the surface of the Earth to change As the rocks undergo stress, they slowly change shape and volume They also move up and down or sideways Types of Stresses Compression squeezes the rock (Convergent) Tension causes the rocks to stretch out over a larger area (Divergent) Shearing of the rock causes it to twist or tear (Transform) Faulting A break or a crack along which rocks move Earthquakes are sometimes along these faults If the rock above the fault moves down, the fault is termed normal (tension), whereas if the rock above the fault moves up, the fault is termed reverse (Compression) Faulted Mountains and Valleys Mountains formed when there are many normal faults in one area Blocks of rock are uplifted Valleys may form when the block of land between 2 normal faults slides downward Folded Mountains • When stress is applied to the rock formation and it bends but doesn’t break • Forms an anticline which is an upward fold and a syncline which is a downward fold Anticline v. Syncline Synclines Sink Volcanic Mountains Single peak mountains formed from volcanoes Yellowstone Yellowstone Super Volcano Alert