GEOLOGICAL PROCESSES Has Britain always been in the same place on Earth? What causes Earthquakes and Volcanoes? How do scientists come up with new ideas to explain what they observe? When do their ideas become accepted by other scientists? Name Class Date Teacher ____________________________ __________ __________ ____________________________ CORE BOOKLET 10 This is the end of the core Chemistry course. Other booklets in this course are 1, 2, 3, 4, 5, 6,7,8a,8b and 9. Good luck with your exam! 1 GEOLOGICAL PROCESSES Tick You should: Use the development of the theory of continental drift to display their understanding that observations, through creative thought, lead to an idea to explain them but the explanation may not be accepted until sufficient evidence exists, as follows: In 1915, Alfred Wegener suggested that the Earth’s continents were once joined and had moved apart to their present positions He based his idea on the close fit of coastlines, and the similar patterns of rocks and fossils, of continents separated by large oceans He was unable to convincingly explain how the continents could move The current theory of plate tectonics became widely accepted in the 1960’s, by which time other scientists had found evidence to show that it is the Earth’s plates that move and that they do so as a result of convection currents in the mantle. Use evidence about the location of earthquakes and volcanoes to appreciate that the Earth’s lithosphere is composed of a number of large pieces called plates, which are moving very slowly, and know that this movement drives the rock cycle Know that rocks can be: Formed where tectonic plates move apart and magma rises to fill the gap producing new igneous rock Deformed and/or recycled where tectonic plates move towards each other driving down the denser plate which may melt to form magma that on cooling forms igneous rock Summary Sheet 2 The theory of plate tectonics The outer layer of the Earth’s crust – the Lithosphere is not a continuous structure but is split a little like the cracked shell on a hard boiled egg: The result is a series of plates floating on the hot mantle beneath. Heat in the mantle creates convection currents that cause the plates to move. Plate margins exist where the plates meet. The history of the Earth’s plates – see also http://tanasi.gg.utk.edu/courses/101/public/BBC/default.html The beginning of time 3 Map – plates and continents of the World – today. 4 Plate Margins – where plates meet Earthquakes and volcanoes (evidence of unrest in the Earth), help locate the edges of plates known as plate margins or boundaries. Take for example the ‘Ring of Fire’ around the Pacific. Volcano’s can be joined together using a ‘dot to dot’ technique. The pattern that follows exactly matches known plate margins. 5 Different types of plate margin and how they contribute to the formation and deformation of rocks. As plates move; they can push together or move apart. 1. Moving apart – CONSTRUCTIVE, e.g. Atlantic mid-ocean ridge. The floor of the Atlantic Ocean is widening as plates are moving apart. As magma gradually rises and cools between plates new rock called igneous rock is formed. Formation and uses of Igneous Rocks The word igneous means fire. Igneous rocks are formed directly from magma as it cools. The type of igneous rock depends upon the speed at which magma cools. Slow cooling – intrusive igneous rock Igneous rocks such as granite are formed when magma finds weaknesses and intrudes into the crust. As it does so it cools and solidifies slowly below the Earth’s surface. This process often occurs during plate tectonic activity; either when plates push together or move apart. Granite only appears when rock above has been worn away; it is younger than the rock that surrounds it. Igneous rocks such as granite can take hundreds of years to form. Granite is a very hard rock used in building and road making. Fast cooling – extrusive igneous rock Igneous rocks such as basalt or obsidian are formed when magma erupts from a volcano as lava and cools on reaching the surface. Basalt cools and solidifies quickly over a number of days. 6 Appearance of Igneous Rocks This is the intrusive igneous rock GRANITE. Granite take hundreds of years to form It is made up of RANDOM, INTERLOCKING crystals. There are no bands, swirls or fossils present Intrusive igneous rocks This is the extrusive igneous rock OBSIDIAN Obsidian takes days/weeks to form It contains small/no crystals There are no bands, swirls or fossils present intrusive igneous rocks such as pumice contain lots of air pockets 2. Pushing together Extrusive igneous rocks - destructive e.g the Andes and Himalayas In the above diagram the continental crust is pushing harder than the lighter oceanic crust. This is similar to the plate margin responsible for the Asian tsunami. On the left of the diagram the oceanic crust or plate is being forced under the continental plate. This is called subduction. Rock at the bottom of the oceanic plate is re-melted. This is called deformation. Meanwhile as the continental crust is forced upwards, magma also moves upwards and cools forming new rock. This is called uplift. Mountains/igneous rock are formed in this way. 7 The Rock Cycle Together deformation and mountain formation form part of the rock cycle. During this cycle rock is constantly being created and destroyed. Wegener and the theory of plate tectonics. Utter, damned rot!" said the president of the prestigious American Philosophical Society. "If we are to believe this hypothesis, we must forget everything we have learned in the last 70 years and start all over again," said another American scientist. Anyone who "valued his reputation for scientific sanity" would never dare support such a theory, said a British geologist. All this was said of Alfred Wegener’s theory in 1915 that the crust was not one continuous land mass but was divided into plates. He also proposed that the Earth’s continents had once all been part of one large super continent which he called Pangaea. Wegener based this on several pieces of evidence; 1. Wegener noticed that despite being separated by an ocean, South America and South Africa look as though they could fit together like pieces of a jigsaw puzzle. 2. Fossils of plants and animals from different sides of the Atlantic were the same. 3. Rock strata in North America and the Scottish Highlands appeared to match. 8 Wegener’s theory that continents making up Pangaea had drifted wasn’t accepted until two Cambridge University scientists found further evidence in the 1960’s from looking at magnetic field patterns at the bottom of the Atlantic Ocean. Wegener died at 50 on a rescue exhibition to Greenland. END OF SUMMARY SHEETS 9 Convection Currents – see worksheet Describe what you did and write/draw your observations. 1. Describe what you did and write/draw your observations. 2. 3. Describe/draw and label what happened when the two bottles were placed on top of one another. 10 4. What causes the Earth’s plates to move – answer this question fully, use the worksheet to help you. _______________________________________________ _______________________________________________ _______________________________________________ _______________________________________________ _______________________________________________ _______________________________________________ _______________________________________________ _______________________________________________ 5. Draw a diagram to represent convection currents in magma. 11 ASSESSMENT INTRODUCTION If, on the Sunday morning after Christmas 2004, you had been like some all-seeing, all-knowing deity, able to peer down through the ocean depths off the western coast of the island of Sumatra, here is what you would have seen: Two giant tectonic plates, which have been pushing against each other for millennia, suddenly shift. The left plate has been sliding under the right at the rate of a few centimetres a year, but now the top plate suddenly springs up, lifting perhaps 60 feet along a 1,000-mile ridge. Above, the ocean surface hardly ripples. The quake jolted the Earth's rotation enough to trim a couple of microseconds off the clock. Relatively speaking, it was a small blip in the long, violent history of a planet with a molten core, where entire continents have vanished and then reformed. But the seismic bump was enough to displace trillions of tons of water in a few seconds. Silently, invisibly, the water pushed outward at the speed of a jet plane. As it neared shore, the speed slowed, and large waves formed, in some places very large ones. 12 13 What caused the Asian Tsunami on Boxing Day 2004? Gra de What to include to achieve grade G An introduction to the theory of plate tectonics including a diagram/map of the Earth’s plates. An explanation of the history behind the theory of plate tectonics including a mention of Wegener and of the two Cambridge scientists. An explanation of the evidence for plate tectonics at least 5 pieces (3 from Wegener, 1 from the Cambridge scientists and 1 link between volcanos /earthquakes and plate margins) An explanation of continental drift use Britain as an example of a country that has drifted. An explanation of convection currents. Explain what happens at the two types of plate margin destructive and constructive (use diagrams). Explain how they contribute to the formation and deformation of rocks (the rock cycle). Make links between the theory of plate tectonics and the Asian Tsunami. Talk about other examples of the effects of plate tectonics. F E D C B A A* You are encouraged to research and bring in your own resources from home on this topic. Present your assessment on A3 paper. You can stick in photographs. You can use the internet there are tonnes of excellent websites on Geology. Please summarise any researched information and present it in your own words. Large, bright presentation please! Key skill – I.C.T 14