Unit C: Earth s Crust BLM/SM Answer Key

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1 Unit C: Earth s Crust BLM/SM Answer Key SM 7.1 Minerals: Building Blocks of Rocks Students answers may vary, but may be similar to the following: Properties Colour Streak Lustre Hardness Crystal structure Cleavage Magnetism Reaction with certain chemicals Notes and Example Colour is important but you have to be careful. Different minerals can be the same colour. Gold and pyrite are both yellow. Some minerals can be different colours. Quartz can be white, black, gray, violet, or colourless. Geologists scratch a mineral on a streak plate to see the colour of the streak the mineral makes. The colour of the streak gives them a clue as to the identity of the mineral. Pyrite and gold are the same colour, but gold makes a yellow streak and pyrite makes a dark streak. How shiny a mineral is helps the geologist identify a mineral. Obsidian has a shiny lustre and asbestos has a dull appearance. A mineral can make a scratch on any mineral that is softer than it is. Geologists use the Mohs hardness scale to help them compare the hardness of different minerals. Diamond is the hardest mineral. The size of the crystals tells geologists how quickly a mineral cooled from a liquid to a solid. All minerals are crystals. Minerals break or fracture into pieces. The way a mineral breaks helps geologists identify it. Mica always splits into thin sheets. Only minerals that contain iron are magnetic. You can use a magnet to see if a mineral is magnetic. Magnetite will attract or repel a magnet. Some minerals can be identified by their reaction with certain chemicals. Calcite, limestone, and marble react with acidic solutions such as vinegar. BLM Data Table for Investigation 7.2 Students answers will vary depending on minerals. Following is one example: Mineral number Colour Streak Lustre Hardness Magnetism Reaction with vinegar Cleavage Name 1 black pale colour; almost white glassy 2 not magnetic none breaks along flat surfaces biotite SM 7.4 Fossils 1. Fossils are casts, impressions, or remains of organisms that died and were covered by sediment before they decomposed. 2. Most organisms do not become fossils because most dead organisms decompose or are eaten by scavengers. So there aren t many to find. 3. An organism dies and its body is covered by sediment. The sediment and the organism s body gets covered by more layers of sediment and becomes sedimentary rock. Minerals in water replace minerals in the organism s body. After many years, all the minerals in the organism are replaced. You get a fossil that looks like the organism but it is like rock. 4. If you look at sedimentary rock from the top to bottom, the youngest fossils will be at the top and the oldest fossils at the bottom. 486 Unit C Answer Key

2 SM 7.5 Weathering Breaks Down Rocks Mechanical Weathering What causes this type of weathering? Chemical weathering happens when there is a chemical reaction between material in a rock and another substance like water or air. What is an example of this type of weathering? Plant roots growing in cracks help split rocks. OR Lichen produces an acid that wears down rocks. SM 7.6 Erosion Gravity: The force of gravity causes rocks to fall. Example: Hope Landslide Wind: The wind carries dust, sand, and soil for many kilometres. Example: Prairie drought in the 1930s Water: Rivers can move rocks, gravel, sand, and mud from the land it crosses. Example: The Fraser River carved out the Fraser Canyon Ice: The weight of the ice causes glaciers to move slowly downhill and cut deep valleys that fill with water to form fiords. Example: Howe Sound and Knight Inlet SM 7.8 Rock Cycle After you read Students completed diagrams should be similar to Figure 1, page 210 of the Student Book. Rock family Sedimentary Metamorphic Igneous How rocks in this family are formed Rocks on the surface of Earth wear down into sediments. Sediments are carried to the bottom of lakes and oceans. Layers of sediment pile on top of each other. Pressure compacts lower layers of sediments to form sedimentary rock. Igneous and sedimentary rock are pushed far beneath Earth s surface. The pressure and temperature changes the rocks into metamorphic rock. Metamorphic rock that is deep enough under Earth s surface will melt to form magma. Magma can erupt out of a volcano and cool to form extrusive igneous rock. Magma can cool beneath Earth s surface to form intrusive igneous rock. BLM 7.0 Chapter 7 Quiz 1. T 7. E 2. F. 8. J 3. F 9. G 4. T 10. H 5. F 11. K 6. F 12. C 13. A 14. B 15. D 16. F 17. I 18. Magma is molten rock material under the surface of Earth. Lava is magma that has been forced out onto Earth s surface. 19. The four factors that cause erosion are gravity, wind, water, and ice. 20. Weathering is the breakdown of natural materials, such as rock, into smaller pieces. Erosion is the movement of rock material from one place to another. Weathered material is often moved during the process of erosion. 21. When water freezes in the cracks of rocks it expands and exerts a force on the rock. Pieces of rock can break off. This process, known as ice wedging, is a form of mechanical weathering. Glaciers moving over the surface of the Earth can move rocks and soil that are attached to the bottom of the glacier. This is one of the ways that rocks and rock materials are eroded. 22. Student descriptions of the rock cycle will vary but should include the following points: Molten rock, or magma, cools to form igneous rocks. Magma that cools under the surface forms intrusive igneous rock. Magma that erupts to the surface (known as lava) cools to form extrusive igneous rock. Various forms of weathering breaks down igneous rock and other types of rock on the surface of Earth into small particles called sediments. Sediments moved by erosion build up in layers at the bottom of lakes and oceans. Pressure from upper layers of sediment turns lower layers into sedimentary rock. If sedimentary rock is buried to a great depth, heat and pressure changes it into metamorphic rock. Metamorphic rock that is pushed deep into Earth melts to become magma. Unit C Answer Key 487

3 SM 8.1 Earth: A Layered Planet Students answers should include 2 points of information about each layer. These points may be similar to those below. Crust thin layer of solid rock floats on inner layers lighter than material in inner layers up to 50 km thick temperature about 5 C Mantle hot thick layer of solid and partly melted rock moves sluggishly, like thick syrup would feel pressure pushing down on you about 2900 km thick temperature from 1000 C to 4000 C Outer Core dense, hot region made mostly from liquid iron and some nickel flows like mantle pressure very high about 2200 km thick temperature 5500 C Inner Core large ball of iron and nickel pressure keeps material solid about 1250 km thick temperature about 6000 C temperature almost as hot as the Sun SM 8.2 Putting Together the Pieces of the Puzzle Shape of Continents the continents of South America and Africa fit together like pieces of a jigsaw puzzle Fossil Record fossil records showed identical plants and animals on different continents. Ice Age patterns of glacier striations were the same on rock surfaces in South America and South Africa. deposits left by glaciers during an ice age were the same in Africa, India, Australia, and Antarctica Landforms landforms on different continents matched when put together to form Pangaea BLM Pangaea Puzzle Students should connect the shapes in such a way that any movement of the masses is towards a neighbouring landmass. For example, Europe should not be positioned beside Antarctica, but Africa could be moved towards South America. Students should find that continents like South America and Africa fit very closely together, but others do not. Students may conclude that the shape of landmasses has changed since Pangaea perhaps the edges of the landmasses changed as they broke away from each other. SM 8.4 Evidence for a New Theory What new evidence did scientists find by studying the ages of rocks on the ocean floor? The ocean floor was not as old as they had thought. Young rocks were at the top of mid-ocean ridges and got older the farther away they were from the ridges. What new evidence did scientists find by studying the locations of earthquakes and volcanoes? The pattern of volcanoes and earthquakes helped them understand that Earth consists of about a dozen plates of oceanic and continental crust that are continually moving. What new evidence did scientists find by studying Earth s magnetic fields? There are magnetic reversals in parallel strips of rock as you move further away from mid-ocean ridges. What new evidence did scientists find by mapping the ocean floor? The ocean floor is not as flat as was believed. There is a midocean ridge that almost encircles Earth. There are deep narrow trenches running parallel to and near the edges of oceans. After you read Scientists are still working on the question of what makes the plates move. BLM 8.0 Chapter 8 Quiz 1. F 2. F. 3. F 4. T 5. F 6. crust 7. inner core 8. Pangaea 9. continental crust 10 oceanic crust 11. mid-ocean ridge 12. Students will probably respond that when they plotted the locations of earthquakes, volcanoes, and mountains on the map, most were clustered together along certain areas where the tectonic plates meet. 13. (a) The shapes of some continents, e.g., South America and Africa, are complementary (fit together like the pieces of a jigsaw puzzle) and it appears that they were joined together at some time in the past. (b) Identical plant and animal fossils have been found on continents that are now separated by oceans. This suggests that the continents may have been together. (c) The Applachian Mountains in North America match up with mountain ranges in Scotland, and coal deposits in Brazil in South America match up with coal deposits in South Africa. This evidence also suggests that the continents were joined together at one time. 488 Unit C Answer Key

4 (d) Striations or scratch marks caused by glaciers in South America matched glacial striations in South Africa, further evidence that the continents were joined. 14. Models are necessary to illustrate and explain the theory of plate tectonics for the following reasons: the plates are too big to observe directly; oceanic plates are under the oceans and are not accessible; plate movement is very slow and requires millions of years for noticeable change; some areas where plates are moving (e.g., earthquake zones and volcanoes) are too dangerous to observe directly. BLM 9.1 Plates on the Move Divergent Boundaries boundaries where plates are moving apart hot molten magma rises to form new crust called sea-floor spreading when it happens on the ocean floor mid-ocean ridge is an example on the ocean floor on land, this movement forms valleys called rifts an example of a rift is in Thingvellir, Iceland Transform Fault Boundaries boundaries where two plates are slipping past each other most are found on ocean floor San Andreas Fault is one example on land Convergent Boundaries boundaries where plates move towards each other when an oceanic plate collides with a continental plate, the oceanic plate is subducted under the continental plate the Andes Mountains were created this way when two oceanic plates collide, one is subducted under the other this forms trenches like the Mariana Trench in the Pacific Ocean when two continental plates collide, the crust buckles and crumbles the Himalaya mountains were created this way BLM Plate Boundary Movements Sketch 1: Sketches should show 2 similar plates moving apart. Answer for blank: divergent. Sketch 2: Sketches should show 2 dissimilar plates moving together with one going under the other. Answers for blanks: oceanic, continental, convergent Sketch 3: Sketches should show 2 similar plates moving toward each other with one going under the other. Answers for blanks: oceanic, oceanic Sketch 4: Sketches should show 2 dissimilar plates moving towards one another with one going under the other. May show mountains on the upper plate. Answers for blanks: oceanic, continental, convergent Sketch 5: Sketches should show 2 similar plates moving together directly on. May show mountains where plates meet. Answers for blanks: continental, continental, convergent Sketch 6: Sketches should show 2 similar plates moving past each other sideways. May show a river on both plates that has been separated. Answers for blanks: river, continental SM 9.3 Earthquakes 1. Earthquakes at divergent boundaries hot magma rising below the crust pushes upward toward an opening in the crust pressure builds up where the plates are joined pressure is enough to push the plates apart and the crust shakes produces small local earthquakes constant small earthquakes along the Mid-Atlantic Ridge Earthquakes at convergent boundaries an oceanic plate is subducted under another oceanic plate or a continental plate and might get stuck against the top plate. force builds up until the top plate moves suddenly can cause a large earthquake the longer a plate is stuck, the stronger the earthquake will be Earthquakes at transform fault boundaries two plates moving past each other in opposite directions can sometimes get stuck when the forces build up, one plate moves suddenly, causing an earthquake the longer the plates are stuck, the stronger the earthquake can cause powerful earthquakes 2. produces P waves and S waves P waves cause first movements felt in an earthquake S waves make rocks vibrate up, down, or sideways S waves usually cause more building damage buildings sway back and forth tunnels and overpasses collapse fires can start when fuel tanks and gas lines breaks can cause tsunamis BLM The Indian Ocean Tsunami 1. Tsunamis are ocean waves caused by an underwater earthquake or volcano. The sudden movement of the ocean floor creates a wave or waves that travel out from the area in all directions at very high speeds. When they reach shallow water, the waves slow down and become very high. 2. The media reports say that about 300,000 people died as a result of the Indian Ocean tsunami because it is practically impossible to get an accurate count of the number of persons killed. Some people were washed out to sea and their bodies were never recovered. Unit C Answer Key 489

5 3. There was such a great loss of life caused because there was no tsunami warning system in place in the Indian Ocean; people didn t recognize the signs of a tsunami until it was too late to take action to protect themselves. A disaster probably could not have been prevented but a tsunami warning system may have helped to reduce the loss of life in some areas. Education may also have helped people recognize the signs that a tsunami was occurring and that they should move to higher ground. 4. Ordinary people can observe signs of an earthquake, such as the ground shaking violently, or indications that a tsunami is happening, such as the water retreating from the shoreline in coastal areas. If these signs are observed, people should move as quickly as possible to higher ground. 5. There is a tsunami warning system of floating buoys in the Pacific Ocean but not in the Indian Ocean because most tsunamis occur in the Pacific Ocean. They are rare in the Indian Ocean. 6. The west coast of British Columbia is a mountainous area. If a tsunami the size of the Indian Ocean tsunami hit the coast of British Columbia, the elevation of the land would help people. Although some cities are located on low-lying areas, many towns and cities are located at higher elevations or behind mountains. The waves would not reach these areas. SM 9.5 Volcanoes Divergent boundaries usually on the ocean bottom magma pushes through where plates are moving apart lava erupts and cools to form ridges on both sides of the crack sometimes lava reaches above the surface of the ocean to form islands Iceland was formed this way Convergent boundaries volcanoes found on land some of the most powerful happen at convergent boundary magma formed is thick and sticky tremendous pressure builds up so eruptions are explosive when pressure is released Mount St.Helen s erupted in 2004 Hot spots magma collects in pools below the Earth s surface magma melts a hole in Earth s crust and pours out onto the surface and hardens lava is runny so does not erupt explosively underwater volcanoes form a cone-shaped mountain that might rise above the ocean s surface to form an island the Hawaiian Islands formed this way Negative and postive effects of volcanoes can kill people and destroy property people can die from hot ash and poisonous gases and be buried by mudslides people can die of starvation because food sources have been destroyed volcanic ash can block the Sun and cool temperatures volcanic ash improves soil volcanic rock contains minerals and gems like diamonds obsidian (a volcanic rock) can be used for sharp tools like scalpels BLM 9.0 Chapter 9 Quiz 1. (b) 2. (c) 3. (d) 4. (a) 5. (b) 6. converge 7. rift 8. transform fault 9. focus 10. aftershocks 11. A tsunami is a large wave caused by an earthquake at the bottom of the ocean. The movement of the ocean floor moves a large volume of water which creates a wave. This wave then moves out in all directions from the epicentre. 12. (a) convergent boundary (b) hot spot (c) convergent boundary (d) divergent boundary 13. Earthquakes are dangerous because a tremendous amount of energy is released when they occur. The movement of Earth during an earthquake can cause buildings to collapse, power lines to fall, and gas and water lines to break. This can lead to fires and explosions and no water for drinking or fighting fires. Earthquakes can also cause tsunamis that can kill people and damage property. 490 Unit C Answer Key