Transcript Chapter 10
Plate Tectonics and Earthquakes South America splitting away from Africa, the formation of the mid-Atlantic ridge, and the collision of India with Asia all occurred after what major geologic event? A growing number of geochemists and paleontologists suspect that a major impact by an asteroid during the Permian-Triassic times some 245 million years ago caused a disruption of Earth’s ecosystems. Following that asteroid strike there was a massive extinction of many, many life forms. The scientists believe that after those events was the break up of Pangaea; the Supercontinent. What are the types of evidence that support the theory of continental drift? In 1912, German meteorologist Alfred Wegener gave the following evidence to support his theory of Continental drift. The edges of some continents look as though the could fit together like a puzzle. He is the scientist who coined the term “Pangaea, which means “all land”. Although his basic hypothesis was accepted, Wegener did not present enough evidence to convince many people. However, over time other scientists were able to present enough evidence to help support Wegener’s earlier evidence. Fossil clues. Fossils of the reptile, Mesosaurus, have been found in South America and Africa. Another fossil that supports Continental Drift, is the plant called Glossopteris, which has been found in Africa, Australia, India, South America, AND Antarctica. Glacial deposits have been found in South America, Africa, India, and Australia. Rock Clues – Similar rocks have been found at the edges of continents that look as though they should line up with other continents What is the force behind convergent boundaries? The forces of the earth come from within the planet. Convection currents of magma move our continental plates; some have convergent boundaries, others have divergent boundaries and still others have transform boundaries where two plates slip past each other. Our most famous transform boundary is the San Andreas fault in California. At a convergent boundary, where 1 plate subducts under another, where would most of the earthquakes occur? Convergent = coming together Subduct: think submerge, submarine – something that goes Under something else What are the options? On the subducting side? On the uplifting side? On a mountain? On a flat plane? Where would metamorphic rocks most likely be found? Remember : metamorphic = heat + pressure Again, what are the options? In the middle of an open, flat region? At the top of mountains? In mountain valleys? Underground? Which options make the most sense? Where are most earthquakes and volcanoes located? Think about the conditions needed for an earthquake? You might need some type of fault. What kind of fault might it be? If a cross-section of the Earth showed rock lloid Divergent Crosstic from opposite layers being pushed upward directions to form mountains, what type of tectonicParsonic boundary would be inferred? gent Olditic id Gambardelloid Transverse What happens at a continental to continental convergent boundary? They meet and shake hands They smash together and form mountains They pull apart and eventually form huge valleys They are equal forces that slide past each other in opposite directions. What causes earthquakes? Click here for an interesting interactive website http://msnbcmedia.msn.com/i/msnbc/Com ponents/Interactives/Technology_Science/ Science/Earthquakes/zFlashAssets/Earthq uakes_v21.swf What type of pressure or force creates folds in rock layers? • Tension – like a rubber band being stretched out • Compression – squeezing together • Shear – causes rocks on either side of the fault to slide past each other What type of fault is located in California? Hint: It’s already been mentioned in a previous slide! Define the term Focus The focus of an Earthquake is the point at which the energy is first released; the underground point of energy release below the epicenter on the surface. What travels faster, “P” waves or “S” waves? Why? Hint: P = primary S = Secondary P - waves - are Primary waves. They travel with a velocity that depends on the elastic properties of the rock through which they travel. P-waves are the same thing as sound waves. They move through the material by compressing it, but after it has been compressed it expands, so that the wave moves by compressing and expanding the material as it travels. Thus the velocity of the Pwave depends on how easily the material can be compressed, how rigid the material is, and the density of the material. P-waves have the highest velocity of all seismic waves and thus will reach all seismographs first. S-Waves - Secondary waves, also called shear waves. They travel with a velocity that depends only on the rigidity and density of the material through which they travel: S-waves travel through material by changing its shape in the direction perpendicular to the direction of travel. The resistance to shearing of a material is the property called the rigidity. It is notable that liquids have no rigidity, so that the velocity of an S-wave is zero in a liquid. (This point will become important later). Note that S-waves travel slower than P-waves, so they will reach a seismograph after the P-wave. If 2 different locations recorded seismic waves generated by the same earthquake, how would the seismographs indicate which location was closer to the earthquake? Hint: look at pages 306, 307, and 308 in your book to figure this one out. What is the fewest number of seismograph stations needed in order to locate the epicenter of an earthquake? Why? 3 – You can draw a straight line between 2 stations, but the epicenter could be off to one side or the other. You need the 3rd station for the final determination. Station 2 Station 1 Station 3 Why is the Earth’s inner core solid? Hey, I’m under too much pressure here!