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Transcript
Plate Tectonics Section 1: Earth’s Interior Section 2: Convection and the Mantle Section 3: Drifting Continents Section 4: Sea-Floor Spreading Section 5: The Theory of Plate Tectonics Earth’s Interior How have geologists learned about Earth’s inner structure? • Geologists have used two main types of evidence to learn about Earth’s interior: Direct evidence • from rock samples Indirect evidence • from seismic waves Earth’s Interior Geologists cannot look inside Earth • Use an indirect method. Seismic Waves (Earthquake waves) • Study how they travel through Earth. Data reveals several layers Earth’s Interior Earth’s Interior Crust Mantle Outer Core Inner Core Earth’s Interior Crust • Solid layer of rock that includes both dry land and the ocean floor • Between 5 and 40 km thick Dry land • Granite light in color less dense Ocean floor • Basalt dark in color more dense Earth’s Interior Mantle • very hot, but solid rock • about 3,000 km thick Lithosphere • Crust and Upper Mantle region • “Lithos”, Greek for Stone Asthenosphere • Remainder of Mantle • Very soft and hotter than Lithosphere • “Asthenes”, Greek for Weak *Lower Mantle • Solid and extends to the Core region Earth’s Interior Earth’s Interior Core • Mostly Iron and Nickel Outer Core • molten metal (Fe and Ni) that surrounds the Inner Core. • Liquid creates the magnetic field of the Earth Bar-magnet with North and South Poles Inner Core • dense ball of metal (Fe and Ni) Intense pressure prevents it from changing from solid to liquid. Earth’s Interior Pressure and Temperature increase as you move towards the center of the Earth Earth’s Interior Core Earth’s Interior Assessment Questions Why is it difficult to determine Earth’s inner structure? How are seismic waves used to provide evidence about Earth’s interior? List Earth’s three main layers What is the difference between the lithosphere and the asthenosphere? In which layer is each located? Section 1.2 Convection in the Mantle How is heat transferred? • There are three types of heat transfer: Radiation Conduction Convection Radiation The transfer of energy through space. • No direct contact between a heat source and an object. Sunlight warms the Earth Conduction Heat transfer within a material or between materials that are touching. • Holding a hot spoon. Conduction is responsible for some of the heat transfer inside Earth. Convection Heat transferred by the movements of liquids and gases. • Caused by: Density differences Gravity • Density mass in a given volume More heat = expansion = less dense Less heat = contraction = more dense Convection What causes convection currents? • Gravity • Difference in Density of liquids or gases. Gravity pulls denser materials downward • More heat = expansion = less dense = moves upward • Less heat = contraction = more dense = moves downward Convection Convection Currents What causes convection currents in Earth’s mantle? • Heat from the core and mantle causes convection currents in the mantle. Visual Summary of the Three Types of Heat Transfer 1.2 Assessment Questions 1. How is heat transferred? 2. What causes convection currents? 3. What causes convection currents in Earths mantle? 4. What is conduction? 1.2 Assessment Questions 5. What is the role of gravity in creating convection currents? 6. What part of Earth’s interior is like the soup in the pot? What part is like the burner on the stove? (Fig 9) 7. How is heat transferred through space? 8. What is a convection current? 1.2 Assessment Questions 9. In general, what happens to the density of a fluid as it becomes hotter? 10. Describe how convection currents form. 11. Name two layers of Earth in which convection currents take place. 12. What causes convection currents in the mantle? 13. What will happen to the convection currents in the mantle if Earth’s interior eventually cools down? Explain. Section 1.3 Drifting Continents What was Alfred Wegener’s hypothesis about the continents? What evidence supported Wegener’s hypothesis? Why was Wegener’s hypothesis rejected by most scientists of his day? Continental Drift Why do the coasts of several continents match so neatly? • West Africa and Eastern South America seem to fit together like puzzle pieces. Continental Drift Alfred Wegener • Hypothesized that Earth’s continents has moved over time. All part of one large, ancient landmass Drifted apart over time • His idea was called “Continental Drift” Pangaea Ancient landmass • “All Lands” • All continents connected together 300 million years ago Pangaea Slowly broke apart to where continents are located today. • Supported by studying: land features fossils evidence of climate change Pangaea Supporting Evidence • Land Features mountain ranges on Africa and South America lined-up. coal fields in Europe and North America match-up Supporting Pangaea: Land Features Pangaea Supporting Evidence • Fossils Glossopteris • fernlike plant Mesosaurus and Lystrosaurus • land-dwelling dinosaurs Fossils of these organisms are found on many different continents separated by great oceans!! How could that be possible? Supporting Pangaea: Fossils Pangaea Climate • Spitsbergen Present location: Arctic Ocean (Cold!!) • Tropical plant fossils are found there! • South Africa Present climate: Mild/Warm • Deep scratches, caused by glaciers are found in the crust. • Glaciers exist in very cold environments!! *Climates changed because landmasses moved. Hypothesis Rejected!! Wegener was not able to provide a satisfactory explanation for the force that pushes or pulls the continents. • More evidence would be needed. Mountain Formation Wegener hypothesized that when continents collide, their edges crumple and fold. • Huge mountains form. 1.3 Assessment Questions 1. What was Alfred Wegener’s hypothesis about the continents? 2. What evidence supported Wegener’s hypothesis? 3. Why was Wegener’s hypothesis rejected by most scientists of his day? 1.3 Assessment Questions 4. What do the matching mountain ranges in Africa and South America show, according to Wegener’s hypothesis? 5. How would continental drift affect the continent’s climate? 6. According to Wegener, how do mountains form? 1.3 Assessment Questions 7. Who proposed the concept of continental drift? 8. According to the hypothesis of continental drift, how would a world map have changed over the last 250 million years? 9. What evidence supported the hypothesis of continental drift? 10. How did fossils provide evidence for continental drift? 1.3 Assessment Questions 11. Deposits of coal have been found beneath the ice of Antarctica. But coal only forms in warm swamps. Use Wegener’s hypothesis to explain how coal could be found so near to the South Pole. 12. Why did most scientists reject Wegener’s hypothesis of continental drift? 13. Do you think the scientists of Wegener’s time should have accepted his hypothesis? Why or why not? Chapter 1.4 Sea-Floor Spreading Mid-Ocean Ridges • an undersea maintain chain where new ocean floor is produced. divergent (moving apart) plate boundary Chapter 1.4 Sea-Floor Spreading What device is used to map the ocean floor? • Mapped in the mid-1900’s by using SONAR. Underwater soundwaves • How long does the echo take to travel? = distance to the bottom. Mid-Ocean Ridge Chapter 1.4 Sea-Floor Spreading What is the process of Sea-Floor Spreading? • Sea floor spreads apart along both sides of a mid-ocean ridge as new crust is added from below. Evidence of Sea-Floor Spreading What is the evidence of Sea-Floor Spreading? • 1. Molten Material Bubble-shaped rocks found on the ocean floor. • caused only by cooling magma Evidence of Sea-Floor Spreading • 2. Magnetic Stripes Iron in molten rock aligns to magnetic poles Poles “Flip” over many thousands of years • Repeated pattern of north and south orientation. pattern is the same on both sides of the MidOcean Ridge. Magnetic Reversal Stripes Evidence of Sea-Floor Spreading • 3. Drilling Samples Oldest rocks • farther from Mid-Ocean Ridge Youngest rocks • closer to Mid-Ocean Ridge Subduction at Trenches What happens at Deep-Ocean Trenches? • Trenches Opposite of Sea-Floor Spreading • Oceanic rock is forced downward, or subducts, and eventually melts into magma. Deep Ocean Trenches Subduction at Trenches • Together, Subduction and Sea-Floor Spreading act as a conveyor belt cooling magma into new rock (Mid-Ocean Ridges). melting old rock into magma (Trenches) 1.4 Assessment Questions 1.Along what feature of the ocean floor does sea-floor spreading begin? 2.What are the steps in the process of sea-floor spreading? 3.What three types of evidence provided support for the theory of sea-floor spreading? 4.How do rocks along the central valley of the midocean ridge provide evidence of sea-floor spreading? 1.4 Assessment Questions 5.Where would you expect to find the oldest rock on the ocean floor? 6.What is a deep-ocean trench? 7.What happens to oceanic crust at a deep–ocean trench?