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Transcript
Plate Tectonics 1 Structure and Physical Properties of Earth’s Interior Continental Drift vs. Plate Tectonics What was the Evidence Supporting Continental Drift? Alfred Wegner came up with the Continental Drift Hypothesis. His 5 pieces of evidence were: 1) Continents seemed to fit together 2) Similar fossils on each continent 3) Rocks matched (age and composition) 4) Glacial evidence – striations (scratches in rocks matched) + deposits 5) Climate evidence – due to types of fossils found, coal deposits… continents have been in different locations on Earth’s surface Structure and Physical Properties of Earth’s Interior • Lithosphere – Continental Crust – Oceanic Crust • • • • MOHO Mantle Outer Core Inner Core 30 km Crust Rocky What is the lithosphere? The Lithosphere is the crust and uppermost part of the mantle •It is cool, rigid and solid layer broken into plates that move •Oceanic crust is mostly basalt •Continental crust is composed of granite granite basalt What are lithospheric Plates? • Earth’s surface consists of moving pieces of crust called lithospheric plates • Lithospheric plates – Have both continental and oceanic crust • Plate Tectonics is the study of formation, destruction and movement of these plates Earth’s Crust • Composed of THE BIG EIGHT - the eight most abundant elements in the earth’s crust – oxygen, silicon, aluminum, calcium, iron, sodium, potassium, magnesium Continental Crust Oceanic Crust Thickness Average 32 km Less than 10 km Composition Si, O, Al, Ca, Na, K Si, O, Fe, Mg (mafic) (granitic/felsic) Location Crust beneath the continents Crust beneath the oceans Density Less dense than oceanic crust More dense than continental crust The Continental Crust • Average Thickness is 25 miles • May exceed 40 miles in mountainous regions • Granitic Rocks-LOWER density • Up to 4 Billion years old The Oceanic Crust • Average Thickness is 5 miles • Basaltic Rock - HIGHER density • Younger than 180 million years old – (younger than continental crust) MOHO • Mohorivicic Discontinuity – The boundary between the crust and Mantle The Mantle • Consists of the Asthenosphere (upper mantle) and Mesosphere (lower mantle) • Below the crust to a depth of 1800 miles • Composition of the upper mantle is igneous rock peridotite – (changes at a greater depth) The Asthenosphere • Beneath the lithosphere about 130-160 km thick • Upper part of the mantle to a depth of about 660 km • Soft, weak layer easily deformed • Composed of hot molten material that can flow easily The Mesosphere • Depth at 660-2900 km beneath Earth’s surface • More rigid layer • Rocks are very hot and capable of a gradual flow The Outer Core • Liquid layer composed of a nickel & iron alloy (very high density) • 2270 km (1410 miles) thick • Convective flow generates Earth’s magnetic field The Inner Core • Sphere with a radius of 1216 km (754 miles) • Has properties consistent with solids • Composed of mostly Iron (and Nickel) Where is the lithosphere and the Asthenosphere? Review What is plate tectonics? What are the lithospheric plates? What do lithospheric plates consist of? What are the 5 types of evidence supporting the theory of continental drift/ plate tectonics? Review What are the four layers of the earth? What is the state (consistency)/composition of each layer? Review What is oceanic crust composed of? What is continental crust composed of? Which one is thicker? What are the similarities and differences of the lithosphere and the asthenosphere?