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Changes in Earth’s Surface Vocabulary For two-column notes, underlines titles are main ideas Scientific Theory of Plate Tectonics • Based on – Wegener’s Hypothesis • • – Sea-floor spreading • • • • Continents drifted to their current locations South America and Africa were once in contact New lithosphere being created at mid-ocean ridge Rocks are newer closer to boundary Pattern of magnetic reversal mirrored on both side of boundary Pangaea – The original multi-continent Changes in Earth’s Surface Scientific Theory of Plate Tectonics • Evidence • • • • Similar fossils are found on both sides of the Atlantic where continents were once joined Similar rocks are found on both sides of the Atlantic where continents were once joined Glacial deposits found in Africa Tropical plant fossils found in Antarctica Changes in Earth’s Surface Scientific Theory of Plate Tectonics • The theory of Plate tectonics was proposed in 1960s based on the theory of continental drift. – It explains the formation and deformation of the Earth’s surface. • Continents are carried along on huge slabs (plates) on the Earth’s outermost layer (Lithosphere). • Earth’s outermost layer is divided into 12 major Tectonic Plates (~80 km deep). These plates move a few centimeters per year. • Scientific Theory of Plate Tectonics – Causes of Plate Motion • Mantle Convection Mantle Convection Draw this. Be sure to label the boundaries and convection cells LOCATION OF TECTONIC PLATES Types of plate boundaries Divergent plate boundaries: where plates move apart (separating plates) Convergent Plate boundaries: where plates come together (colliding plates) Transform plate boundaries: where plates slide past each other (sliding plates) Types of plate boundaries Divergent (Tension) Convergent (Compression) Transform (shearing) Draw a picture of each Types of plate boundaries Types of Plate Boundaries Divergent • Plates move away from each other (tension) • New lithosphere is formed (we know because the rocks at the boundary are younger than rocks further away) • A divergent boundary in the ocean produces midocean ridges. • A divergent boundary on land produces rift valleys. Types of Plate Boundaries Divergent • As magma cools to form new lithosphere, rocks containing iron are magnetized in the same direction as Earth’s magnetic field. – When the Earth’s magnetic field reverses every 70,000 years, alternate patterns of magnetism are formed. – These patterns mirror each other across the mid-ocean ridge Alternating Magnetic Bands Found in the Ocean Types of Plate Boundaries Divergent: ocean-ocean Types of Plate Boundaries Convergent • Plates move toward each other (compression) • Lithosphere is consumed (forced down into the mantle) • • Oceanic plates are more dense than continental plates There are three types of convergent plate boundaries – Oceanic-continental plate – Oceanic-oceanic plate – Continental-continental plate Types of Plate Boundaries Convergent: ocean-continental • Oceaniccontinental plates collide • Oceanic plate subducts below continental • Forms a subduction zone • Earthquakes and volcanoes Types of Plate Boundaries Convergent: ocean-continental Types of Plate Boundaries Convergent: oceanic-oceanic • 2 oceanic plates collide • One plate dives (subducts) beneath other • Forms subduction zone • Earthquakes and volcanoes • Forms chain of islands called an island arc • Also forms ocean trench Types of Plate Boundaries Convergent: continental-continental • 2 continental plates collide • Neither plate wants to subduct • Collision zone forms high mountains • Earthquakes, no volcanoes example: Himalayas Types of Plate Boundaries Convergent: continental-continental Types of Plate Boundaries Transform • • • • Two plates slide past each other Lithosphere is neither consumed nor destroyed. Responsible for most of the earthquakes Usually occur in oceans but the most famous are on land (like San Andreas Fault) Types of Plate Boundaries Transform Plate Boundary 3 Transform What drives plate movement? • Ultimately: heat transported from core and mantle to surface • Heat transported by convection • Core is ~5,000°C and surface is ~0°C • Where mantle rises: rifting • Where mantle sinks: subduction zones Plate tectonics affect climate • Antarctica was once tropical (fossils of palm trees) but drifted to its current location at the South Pole (frozen) • Distance between continents affect ocean currents, which affect climate Classwork 1 1. What causes tectonic plate movement? 2. Name one way in which we know that the seafloor in the divergent boundary (spreading plates) in the midAtlantic Ocean is creating new ground. 3. ____ boundaries are most often associated with earthquakes 4. This often occurs where oceanic and continental plates meet at a convergent boundary 5. This often occurs where continental plates meet each other at a convergent boundary 6. This often occurs when oceanic plates meet each other at a convergent boundary Copy the questions into your notebook (right-side) and answer them Classwork 1 7. A chain of islands called an ___ ___ may be formed where oceanic plates converge Copy the questions into your notebook (right-side) and answer them