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Thursday, October 29 • Word of the Day: – Theory of plate tectonics: Earth’s outer shell, the lithosphere, is divided into plates that ride on the asthenosphere • Warm-Up: – If you were a scientist trying to prove that the earth is round, what evidence would you give? Monday, November 2 • Divergent boundary: two plates move away from one another • Warm-Up: – Cut out the pieces of the puzzle and try to piece the continents together to form one large continent. – What is this continent called? – What has caused the continents to move to where they are now? 11/4 • Word of the Day: – Convergent Boundary: two plates move toward one another; collide • Warm-Up: – Summarize the 5 pieces of evidence Wegener proposed for the Theory of Continental Drift Chapter 33 Our Restless Planet 33.1 The Theory of Continental Drift • Pangaea – Scientists noticed that the eastern shorelines of South America and the western shoreline of Africa fit like a puzzle – Alfred Wegener proposed that all continents had once been one big land mass • Pangaea – supercontinent that once existed • Broke into several large pieces Evidence • Geological boundary of continent at continental shelf – continental shelf – gently sloping platform between the shoreline and the steeper slope that leads to the deep ocean floor • Rocks from different continents match • Mountain systems in Africa and South America • show evidence of having once been joined Identical fossils have been found on different continents Evidence • Paleoclimatic evidence – Ice once covered parts of several continents – If in present positions, would have covered whole world – No evidence of very cold climate then, but if one continent, the ice evidence makes sense • Idea thrown out during Wegener’s time, but widely accepted today Scientific Revolution – Paleomagnetism – magnetism changes from the past seen in geology • From rocks that form near the earth’s magnetic • • field, we can determine where the magnetic poles have been over time Scientists discovered that the magnetic poles have moved all over the world Provided proof the continents had drifted Mapping of Ocean floors • Found huge mountain ranges, deep ocean • trenches, and volcanic activity H.H. Hess proposed seafloor spreading – – – – Seafloor constantly made new Underwater mountains form convection cells moving up New lithosphere forms at Mid-ocean ridges Earth Recycled 11/5 • Subduction: one plate slides underneath another • Warm-Up: – Which type of plate boundary would form mountains? – Why? – Which type would form big valleys? – Why? Calculation Corner • We can use calculations to figure out how fast things are moving or spreading. • With your group, do the calculation corner on page 596 in the book. – Look through the example – Then, answer the “Your Turn” questions at the bottom Thursday, November 5 • Word of the Day: – Transform fault boundary: two plates move horizontal (side-side) relative to one another • Warm-Up – Brainstorm: What are some structures on earth that could have been formed from plate boundaries? 33.2 The Theory of Plate Tectonics • Theory of Plate Tectonics – Earth’s outer shell, • • • the lithosphere, is divided into 8-12 large plates and a number of smaller ones Lithospheric plates float on the plastic asthenosphere Interiors of plates are stable All interactions occur along plate boundaries; why we see earthquakes, volcanoes, and mountains at similar places 33.3 There are 3 Types of Plate Boundaries • Divergent Boundaries – Two plates are moving apart – Created by tension forces • Convergent Boundaries – Plates come together – Created by compression forces • Transform-fault Boundaries – Plates slide horizontally past each other Divergent Boundaries – Mid-Atlantic Ridge: spreading center, making Atlantic Ocean grow • Ground younger near the ridge, older as you move away • Spreads at about 2 cm a year – Rifts or Rift Valleys: spreading centers on land • Example: Great Rift Valley of East Africa • May become a new ocean basin one day Convergent: Oceanic-Oceanic • Subduction occurs: One plate drops below the other one – Forms a deep ocean trench – Crust deep in trench melts, produces magma which can lead to volcanic island arcs Convergent: Oceanic-Continental • More dense ocean plate goes below the less dense continental plate (subduction) • Forms chains of volcanic mountains on the continental plate – Ex: Andes in South America, Sierra Nevada and Cascade Ranges in the Western US Convergent: ContinentalContinental • Compression causes breaks and folds in both plates – Crust is very thick – No volcanoes, but lots of earthquakes • Produces Mountain Ranges – Ex: Himalayas in Asia and the European Alps Transform-Fault Boundaries • Lithosphere is not created or • • destroyed Same motion as strike-slip faults San Andreas Fault is most famous Transform-Fault – Pacific plate moves North about 5 cm a year – San Andreas responsible for about 3.5 cm of that 5 33.4 The Theory that Explains Much • Plate Tectonics directly relates to rock types and • • • formation Metamorphic rocks form in areas of subduction and continental collisions Melting ocean floor creates magma, when it cools it produces Igneous rock such as granite or basalt Sedimentary rocks form from the weathering of mountains, which are formed by plate tectonics. Review: • Hold up a: – 1 for Divergent – 5 for convergent – 10 for Transform fault Questions • San Andreas is an example of this – 10 • Causes mountain ranges –5 • Could create a new island in Africa –1 • Creates Rift Valley and mid-ocean ridges –1 Questions • Creates volcanic island arcs –5 • No earth is created or destroyed – 10 • Caused by tension forces –1 • Horizontal (side-to-side) movement – 10 11/12 • Take out your homework and homework calendar…Have them out and ready • Word of the day: – Rifts: large down-faulted valleys created by spreading centers • Warm-Up: – A woman sits in the warmth of a natural hot spring located in the quiet and peaceful mountains. How is that spring warmed? Monday, November 9 • Rift Valley: large down-faulted valleys created by spreading centers • Warm-Up: – Get a map off the front desk. At each of the 3 locations given on the map, tell me what you would be wearing – Explain the difference between longitude and latitude. Tuesday, November 10 • Mineral: a naturally occurring, solid substance made of only one element or compound • Warm-Up: Explain how the different plate boundaries form mountains, volcanoes, and volcanic islands – List any veterans or current military people that you know…Be sure and thank them for serving our country!