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Plate Tectonics Unit: Composition of the Earth: Layers of the Earth: 1. Crust: 5-100km thick. a. Oceanic crust: thin and more dense, mostly basalt b. Continental crust: thicker and less dense, made up of more granite than oceanic crust Layers, Continued: 2. mantle: made of molten (melted rock), very thick, 2,900 km, and likely to have convection currents. 3. Outer Core: molten iron, 2,200 km thick 4. Inner Core: solid but very hot iron, 1,230 km thick The core makes up 33% of Earth’s total mass Tectonic Plates: Because of convection currents in the mantle, plates of the earth’s crust move around as they “float” on the mantle. Over many millions of years, the location of the oceans and continents have changed dramatically, and surface features like valleys and mountain ranges are continually created and destroyed. Wegener’s Theory of Continental Drift: In 1910, a German scientist named Alfred Wegener proposed that the continents had, in the very distant past, been joined together in one supercontinent he called Pangea, and had since drifted apart into separate continents. He called this theory Continental Drift. Wegener’s arguments in support of his theory: 1. Evidence from landforms: • Continents along the Atlantic Ocean appear to fit together like puzzle pieces. • Mountain ranges in South Africa match up with mountains in South America. • Coal deposits in Europe match up with coal deposits in North America. 2. Evidence from fossils: • Fossils of the same species of land animals and land plants had been found on different continents; they could not have crossed oceans. • Fossils of tropical plants were found on the island of Spitsbergen, which is well north of the Arctic Circle. Wegner proposed that this island had once been close to the equator. • Evidence of glaciers had been found in South Africa, which currently has a subtropical climate. Wegner thought South Africa must have been much farther south millions of years ago. Unfortunately, no one believed Wegener at the time. His evidence was not totally convincing, and he could not explain what force could cause whole continents to move. Plate Tectonics: Wegener was Right! Starting in the 1960’s, as scientists started mapping the ocean floor, they discovered that the ocean floor was spreading out along the Mid-Ocean Ridge. This very easily explained how continents could move. How Sea-Floor Spreading Works: Evidence for Sea-Floor Spreading: 1. 2. 3. Rock samples from the ocean floor close to the mid-ocean ridge are younger than rock samples farther away. Magma can actually be observed oozing up from the mid-ocean ridge, and cooling into rock. Iron samples from the ocean floor alternate their patterns, showing that some parts of the ocean floor were formed at times when the magnetic poles were reversed. Subduction at Deep Ocean Trenches: The Ultimate Cause of Plate Movement? Convection! Tectonic Plates of the Earth: Homework: LO: Describe the theory of plate tectonics SLE: Communicate ideas clearly and articulately 1. Read p. 108-111 2. Answer review questions on p. 111 Types of Plate Boundaries: LO: Describe the theory of plate tectonics SLE: Meet or exceed NGSS Checkpoint Quiz on Plate Tectonics: 1. List the layers of the interior of the earth, starting with the middle and going outwards. 2. How do we know the earth’s core is solid? 3. Give one piece of evidence that the seafloor is spreading. 4. Give one of Wegener’s arguments in favor of his theory of continental drift. 5. Describe three types of plate boundaries (OK to draw diagrams). LO: Describe the theory of plate tectonics SLE: Meet or exceed NGSS Checkpoint Quiz on Plate Tectonics #2: 1. Describe the process of sea-floor spreading. 2. Give one piece of evidence that the sea floor is spreading. 3. What causes the formation of most mountain ranges? 4. Name three types of plate boundaries, and describe the movement of plates along each one (diagrams OK) (2 points) The Effects of Tectonic Plate Movement on Earth’s Surface : Plate movement causes the earth’s surface to deform (noun: deformation): layers of rock bend or break because of the stress placed on them. Main Types of Stress: Compression: When two plates are squeezed together. Tension: When two plates are pulled apart. Shearing: when two plates are pulled past one another. Folds: Folding is the bending of rock layers due to one of these three types of stress. Types of folds: Anticlines: upward-pointing folds. Synclines: Downwardpointing folds. Monocline: A step-like fold in which both ends are horizontal. Faults: Faults are regions where rock areas break and slide past each other. When faults are not totally vertical, the upper part is called the hanging wall and the lower part is called the footwall. Types of Faults: Plate Tectonics and Mountain Formation: The motion of Earth’s plates causes mountains to form, mostly at plate boundaries. The type of mountains that are formed depends on what type of plate boundary it is. Types of mountains: Folded Mountains: When plates are squeezed together and pushed upward. These are usually formed at convergent boundaries. Fault-Block Mountains: When plates move apart and one section of rock drops down relative to other sections. (These tend to be smaller mountains.) Volcanic Mountains: Formed by volcanic eruptions, usually near subduction zones. Homework: LO: Describe effects of the movement of tectonic plates. SLE: Articulate ideas clearly and effectively. 1. Read p. 112-118 2. Answer review questions on p. 119 Earthquakes: Where earthquakes occur: Most earthquakes occur at or near plate boundaries. The crust moves more often in these places, and stress is more likely to build up there. The cause of earthquakes: Rock at plate boundaries or along faults will stretch as sections move past one another, but eventually so much pressure builds up that the rock breaks and snaps back (like a rubber band), which releases waves of energy. The sudden snapping back of rock is called elastic rebound. http://wn.com/elastic_rebound_and_earthquak es Seismic waves: Seismic waves are energy waves caused by rock vibrations along a fault. There are 3 kinds of seismic waves: 1. Primary (P): The first to arrive (the fastest). They compress and expand like a Slinky. 2. Secondary (S): They come after primary waves. They move from side to side and up and down. S waves, unlike P waves, can not travel through liquids. 3. Surface waves: P or S waves that have reached the surface. These are the waves that cause the most damage, although they are slower than the other two. How earthquake strength is measured: Earthquakes are detected, located and their strength measured by a machine called a seismometer. They record the movement of the earth using a needle; the more the ground shakes, the more the needle does, too. Earthquake measuring scales: 1. Mercalli Scale: Developed early in the 20th century, this scale does not measure the energy precisely, but records the amount of damage that has been done. 2. Richter Scale: Developed in 1930, it measures the strength of an earthquake according to how much motion the nearest seismometer has recorded. This could change depending on how far away from the earthquake the seismometer is. 3. Moment Magnitude Scale: This is the scale used today. It measures the total energy produced by the earthquake, not the results of the earthquake. In this scale, each magnitude is ten times larger than the next lowest number. Epicenter vs. Focus: Focus: The location below ground where the earthquake begins. This can be many Km below the surface. Epicenter: The first location on the surface where the earthquake can be felt. Homework: LO: Describe cause and effects of earthquakes. SLE: Meet or exceed NGSS. 1. Read p. 130-139 2. Review questions on p. 139 LO: Describe the cause and effects of earthquakes. SLE: Meet or exceed NGSS Checkpoint Quiz on Earthquakes: 1. Draw diagrams of normal, reverse and strike-slip faults. For each type of fault, label the foot wall, hanging wall, and the direction of movement along the fault. 2. What causes earthquakes? 3. Where on on Earth are earthquakes most likely to occur? 4. What device is used to measure the amount of energy produced by earthquakes? 5. What’s the difference between an epicenter and a focus of an earthquake? Earthquake Safety: The likelihood of experiencing an earthquake depends on where you are. If you live near a plate boundary, your earthquake hazard level is higher. Forecasting Earthquakes: Predicting when and where the next earthquake will occur is very difficult. However, scientists sometimes try the Gap Hypothesis: Areas along faults that haven’t had an earthquake in a while are more likely to experience a strong one in the future. Earthquake-Proof Building Design Features: Mass Damper: A weight placed on the roof to keep the building from swaying. Shear wall: braces in walls to prevent them from tearing in half. Active tendon system: Shock absorbers built into the frame of the building. Base isolators: Felxible layers of material built into the foundation of the building. Pilings: In soft soil, long posts underground attached to the bedrock below the surface. Cross braces: To keep the building from shaking apart. Flexible pipes: To prevent fires from gas leaks. What to do during an earthquake: • Drop, cover and hold • Wait 100 seconds in case of immediate aftershocks • Quickly and calmly exit the building • Gather in an open area and await instructions from trusted adults. Homework: LO: Identify and describe earthquake-resistant design features SLE: Work independently 1. Read p. 140-145 2. Review questions p. 145 LO: Identify and describe earthquake-proof design features. SLE: Work collaboratively. Design and build an earthquake-proof building. Materials: 100 3 x 5 cards, 1m masking tape, 10 straws. Rules: 1. You may only use the materials provided. 2. Building must be at least 50cm tall and 20cm wide. 3. Building must be free-standing. 4. Building must have 4 or more earthquake design features. 5. Must be able to withstand shaking for 30 seconds. Volcanoes: A volcano is a crack or weak point in the earth’s crust through which magma comes near or onto the surface. (Once magma reaches the surface, it’s called lava.) Magma: below ground Lava: above ground Types of volcanic eruptions: Explosive: Non-explosive: Structure of a volcano: Products of Volcanic Eruptions: • Lava: the thickness of lava is determined by the amount of the mineral silica- the more silica, the thicker the lava. • Volcanic ash: dust and small bits of rock from explosive eruptions • Bombs: large rocks • Lapilli: small rocks • Gas: mostly CO2, but also toxic gases • Pyroclastic flow: an avalanche of hot gas, ash and dust that flows down the side of the volcano at very high speeds. LO: Model effects of pressure on volcanic eruptions. SLE: Work Collaboratively Problem: What effect does increased pressure have on the force of volcanic eruptions? Hypothesis: Procedure: 1. Place 50ml of vinegar in the bottom of a flask with a wider opening. 2. Add 2-3 tsp of baking soda, and observe what happens. 3. Repeat steps 1-2 with a flask with a narrow opening 4. Compare observations. Data: Using words or pictures, describe what happens with each “volcano.” (qualitative data) Conclusion: Types of Volcanic Landforms: A volcanic landform is a feature of the earth’s surface that is created by volcanic eruptions. These include: • Shield volcanoes • Cinder cone volcanoes • Composite volcanoes • Lava plateaus • Calderas Shield Volcanoes: Shield volcanoes are created by many layers of non-explosive (lava-only) eruptions. They have very gentle slopes, and can even be flat, but some of them are enormous. (The tallest mountain on earth is a shield volcano.) Cinder Cone Volcanoes: Cinder cone volcanoes result from small to medium –sized explosive eruptions, and are made almost entirely of ash and dust (pyroclastic material). They tend to be small, but have very steep sides full of loose material. Composite Volcanoes: Composite volcanoes are formed by alternating explosive and non-explosive eruptions. Inside, they have alternating layers of ash and lava. They are often dormant for thousands of years, but can also produce extremely large, destructive explosive eruptions. (All four of WA’s volcanoes are composite volcanoes.) Lava Plateaus: Lava plateaus are formed when thin lava flows out from one or more long cracks in an area. Over many thousands or millions of years, many layers of lava form a high flat area (plateau). Some lava plateaus are gigantic: the Columbia Plateau in WA is a lava plateau. Caldera: Sometimes, explosive eruptions are so large and violent that the entire magma chamber beneath a volcano empties out all at once. With nothing below to support the weight of an entire mountain, it collapses in on itself and forms a gigantic hole in the ground called a caldera. Homework: LO: Identify and describe volcanic landforms. SLE: Articulate ideas clearly and effectively. Write a 7-sentence (more is OK) paragraph that describes each major type of volcanic landform. Include a description of how each one is formed and what it looks like.