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Transcript
Plate Tectonics Continental Drift • Alfred Wegener • German polar researcher, and meteorologist. • hypothesized that the continents were slowly drifting around the Earth. • His hypothesis was controversial and not widely accepted until the 1950s, when numerous discoveries such as palaeomagnetism provided strong support for continental drift, and thereby a substantial basis for today's model of Plate tectonics Pangaea the super continent approx. 250,000,000 Evidence: Shorelines appear to match (like pieces of a puzzle) Matching rock types and structures Evidence: Matching fossils on different continents Ancient climates Large grooves Carved by glaciers Are found in Tropical areas Large coal fields of N America and Russia were once at the equator http://www.ucmp.berkeley.edu/geology/tecall 1_4.mov Rejecting the Hypothesis No way to explain the mechanism that would be able to move whole continents about in the ocean. After WWII there was a surge In advanced technology used To advance scientific research. Extensive studies of the Ocean floor revealed Much about the Layers of the Earth Mafic basalt Felsic granite Plate Tectonics Major discoveries In science & technology Allow scientists to Develop the Theory Of Plate Tectonics The Earth’s surface is divided into large plates That move about on the “plastic” asthenosphere What makes the plates move Radioactivity- Heat energy from decaying radioactive elements Uneven heat in the Mantle causes CONVECTION CURRENTS The solid lithosphere is broken into pieces and moves on top of the “weak” or “plastic” asthenosphere. This movement explains the cause of earthquakes, volcanoes, oceanic trenches, mountain range formation, and many other geologic phenomenon. Types of Plate Boundaries • Divergent Boundary Lithospheric plates move apart Seafloor spreading and A Mid-Ocean ridge KEY Words: rift, ridge Older rock Older rock Younger rock Youngest rock is found near the ridge, oldest rock is near the continents Locations: Red Sea Great African Rift Zone Mid-Atlantic Ridge A divergent boundary Africa’s Great Rift Valley Can you find it on a map? Convergent Boundaries Ocean – Continental Boundary Locations: Andes Mt.s Cascade Mt.s (can you find these on a map? Key Words: Subduction trench Convergent – oceanic- oceanic Locations: Japan Philippines Indonesia Aleutian islands (Find these on a map) What is formed “behind” The string of islands? Key Words: Subduction, Trench Island arc Continental – Continental Convergent Locations: Himilayas Alps (find these on a map) Note: NO subduction zone, NO trench. Mt.s are folded upward. Transform Plate Boundary Location: The San Andreas Fault (find on a map) Evidence - Polar Wandering found in the layers of rocks The following slides show details of more evidence gathered to support Plate Tectonic Theory Evidence: Magnetic Reversal The metallic minerals in The rocks are a “record” Of the direction of the poles At the time of crystalization http://jeffcoweb.jeffco.k12.co.us/isu/science/9earth/maganimation.html Evidence: Seafloor Spreading – each “layer” shows different ages of the rock and demonstrates When there is a polar reversal. (Like a horizontal version of a drill core sample of the deep ocean) Earthquake Patterns When plotting the locations of earthquakes around the world. . They align with Plate boundaries. (all have earthquakes, but not all boundaries have volcanoes, only boundaries with a subduction zone) Ocean Floor Drilling Hot Spots – unusual concentration of heat in the mantle Creates so much heat energy it breaks through the lithosphere In the middle of a plate. Intraplate Hot Spots: Hawaiian islands The plate moves but the hot spot stays in place Intraplate Hot Spot: Yellowstone National Park Unusual Hot Spot on a plate boundary Review: Which type of boundary has upward convective movement? Which type of boundary does downward convective movement occur? What type of plate boundary is there no destruction of the earth’s lithosphere?