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Transcript
In this unit, you will: • Understand Earth’s major geological processes and hazards, and how they shape biological evolution • Know the forces at work driving the tectonic plates, causing earthquakes, and volcanoes 5000°-7000° C In order to understand plate tectonics, you must first be reminded of the dynamics of Earth’s interior. The Kola Superdeep Borehole drilled in the Kola Peninsula in Russia is the second deepest hole in the world, nearly 12,262 meters (7.6 miles) It was drilled with the intent of reaching the Moho, but as drilling cost increases with depth, it is unlikely to happen any time soon! • Generally, thinner under oceans, thicker under continents • Both brittle, and bendable • Vents form along volcanic hot spots, to allow interior materials to spill out onto the surface. • The boundary between the crust and the mantle is known as the “Moho”. Earthquake waves here change direction, and move faster. Rodinia Evolution slows down… The mantle can be broken down Evolution speeds up… into an upper region which greatly influences the crust above (the asthenosphere), and the lower mantle. Convection currents within the mantle are responsible for driving the tectonic plates. The Earth’s mantle is important, because it causes the movement apart, and together of the continents. This has influenced environments and therefore evolutionary patterns and processes over the millennia. The mantle is composed of a non-newtonian fluid, becoming more and more viscous the closer it gets to the crustal boundary. It behaves like a fluid when pressure is released, and a solid when compressed. https://youtu.be/ryrXAGY1dmE 1. What influence does Earth’s hot interior have on the Planet? 2. Because Earth’s crust can bend and break, what structures form? 3. Why are volcanoes important in their influence on the biosphere? 4. What is the Moho, and how do we know where it is? 5. What causes the tectonic plates to move? 6. What are the evolutionary consequences of tectonic movement? The important thing to remember about the Earth’s core is that it is composed of two separate parts. • Fluid outer core • Solid inner core The inner core is under such extreme pressure, that even though temperatures would permit the fluidity of iron, it remains a solid. The outer core is important for two reasons: • its temperature and convection influence convective currents within the mantle, and… • the inner and outer cores’ differential spinning speeds, and direction creates the magnetic field protecting the Earth. 7. What area is ultimately responsible for the convection currents within the mantle? 8. What is the significance of the different spin velocities (speed and directions) within the Earth’s core? 9. What is created that helps protect Earth from solar debris? About a dozen large plates exist within the crust of the Earth, and as mentioned earlier, are in constant motion. They ride upon the convective currents within the upper mantle, known as the asthenosphere. They move at about the same rate as your fingernails and hair grow. Nearly all of the geologic activity takesand place near or Volcanoes Earthquakes at the boundaries of This geologically significant area is knownthese as thetectonic “Ring of plates…at areas Fire”, and it circumnavigates the Pacific Ocean. Along its called “hot spots” borders are some of the most active areas on the planet. Plates that move together (Destructive boundaries) Earth’s tectonic plate boundaries have three Convergent plates possible outcomes… Oceanic-Continental Continental-Continental • They can move together Oceanic-Oceanic • • They can spread apart • They can slide against each other 10. What is a geologic hot spot (not to be confused with an ecological hot spot)? 11. Where is the “Ring of Fire”, and why is it geologically significant? 12. A tectonic boundary that moves together, or is destructive, is known as what? 13. What forms when convergent boundaries exist between • Oceans and Continents? • Two continents? • Two oceanic plates? • Plates that move apart…Constructive boundaries Divergent Plate Boundaries When they occur in the ocean… When they occur on the continents… Iceland…where the MidAtlantic Ridge emerges from the Ocean East African Rift Valley…will someday be a sea floor. Most earthquakes occur at plate boundaries, where two plates are colliding or grinding up against one another. • Transform faults occur when one plate “slips” past another Deep Ocean Assessment and Reporting of Tsunamis The greatestuse risks in We currently warning buoys The greatest risk of the When earthquakes happen on earthquakes is death, due to to detect seismic ocean waves. tsunami is the coastal the ocean floor, huge waves building failure (collapse) Many areas of the ocean have devastation caused. called tsunamis may occur. when they’re not up to code. none. 14. A tectonic boundary that moves apart, or is constructive is known as…? 15. What forms along divergent plate boundaries… • When they occur in the ocean? • When they occur on continents? 16. While earthquakes can occur along any type of tectonic boundary, they are most common along… 17. What forms many times when earthquakes occur near to or beneath the ocean? 18. What is the greatest risk in an earthquake? 19. How do we detect tsunamis? Similar to earthquakes, volcanoes occur in areas known as geologic hot spots, typically, where oceanic crust is converging with continental crust…in areas of subduction. The most dangerous result of a volcanic occurrence is not the viscous lava, but the ensuing flood of mud mixed with ash, and debris known as a “lahar”. Very few volcanoes actually produce lava!!! Pyroclastic flows are also dangerous. Again, the “Ring of Fire”, a highly seismically active area that circumnavigates the Pacific Basin, is beautifully illustrated in this map. Some volcanoes do not appear to be located by tectonic boundaries at all. These special volcanoes are known as “hot spot volcanoes”. Examples would include oceanic hot spots, such as the Hawaiian Island chain, and continental hot spots…such as Yellowstone. The study of volcanoes by volcanologists is both interesting, and important. Volcanoes are thought to be responsible for Earth’s second atmosphere, through outgassing. Where’d all the oxygen come from? Earth’s modern atmosphere was thought to have originated through the process of photosynthesis by early microbes known as cyanobacteria. 20. Why are converging subduction zones most often associated with volcanoes? 21. What two features of most volcanic eruptions put people most at risk? 22. How are hot spot volcanoes different from simple convergent/subduction-caused volcanoes? 23. Give two examples of hot-spot volcanoes. 24. Describe how volcanoes contributed to Earth’s early atmosphere, and where our modern atmosphere came from.