1. Mrs. Neistadt Physical Science

2. The theory of plate tectonicsexplains the movement ofcontinents and other geologicalevents like earthquakes andvolcanoes. The term tectonics meansconstruction or building. *The theory of plate tectonics, stated in 1965, refers tothe movement of giant pieces of solid rock on Earthssurface called tectonic plates. 3. In 1915, Alfred Wegener (1880-1930), a German meteorologist, wrote a book titled The Origin of Continents and Oceans. *Alfred Wegener gathered evidence that supported his ideathat all the continents had been connected. *This was the Theory of Continental Drift. 1915 4. In the early 1960s, Henry Hess(1906-69), a geologist andformer commander of a Navyship equipped with an echosounder, used the profile ofthe sea floor to propose that itwas spreading at the mid-ocean ridges. An echo sounder is used to make a profile of the sea floor. 5. *Harry Hess *An Americangeologist who studiedmid-ocean ridges. *He suggested that theocean floors move likeconveyor belts, carryingthe continents alongwith them. 6. The theory of plate tectonicsexplains the movement ofcontinents and other geologicalevents like earthquakes andvolcanoes. The term tectonics meansconstruction or building. *The theory of plate tectonics, stated in 1965, refers tothe movement of giant pieces of solid rock on Earthssurface called tectonic plates. 7. Around the same time,Robert Dietz (1914-95), ascientist with similarideas, coined the termsea-floor spreading. *Sea-floor spreadingdescribes the sea floor oneither side of a mid-oceanridge as moving awayfrom the ridge andcreating a rise or valley. 8. *Hot fluid from the mantle (called magma) enters the rise orvalley and cools, creating new sea floor (also called oceaniccrust). 9. In the 1950s and 1960s,scientists discovered that therocks of the sea floor have a veryinteresting magnetic pattern. *Over geologic time, themagnetic polarity of Earth hasswitched. *Scientists believe the polesswitch because of a magneticinteraction between the planetsinner and outer core. 10. Stripes of rock with anorth-south orientation(normal) alternate withstripes of rock with asouth-north orientation(reversed). The blue and white stripesyou see in the figure are aninterpretation of amagnetic profile. 11. The Earth is like a bar magnet, It has a North and South pole.SketchBar magnet. Iron filingsline up with magneticfield. Concept 12. The Geographic North and Magnetic Northare not in the same place.The asterisk marksMagnetic North or TrueNorth. 13. *The Earths magnetic poles switch direction. The south pole becomes the north pole, and the north pole becomes the south pole *This switch in direction is known as MagneticReversal. Such reversals are caused by changes in Earthsmagnetic field. *Earths Geographic Pole never changes place. 14. *Each Magnetic Reversal is recorded in thesea-floor rock. As the molten material rises and cools, ironparticles line up with Earths magnetic field. When the material hardens, these particlesstay in place like compass needles that arestuck in position forever. 15. *The records of magnetic reversals line up like stripesin a rock Evidence of plate movement is found by finding theage of the rock. The youngest rock shows the last magnetic reversaloccurred about 760,000 years ago. The oldest reversal we have found happened 150million years ago. 16. Can you identify which of the plates are only made of oceanic crust? 17. Use usgs.gov to find earthquakes in real-time to mapthe tectonic plates. 18. There are three main kinds of plate boundaries: divergent convergent transform 19. The tectonic plates that cover Earths surface are pieces ofthe lithosphere that fit together and float on theasthenosphere (a part of the mantle). There are a number of large tectonic plates on Earthssurface, and smaller plates are being identified all the time. 20. Diverging plates move apart and new crust forms. 21. Divergent boundariesare sites of earthquakesand volcanic activity. Mid-ocean ridges andassociated sea-floorspreading occur atdivergent plateboundaries. In effect, a mid-oceanridge is like a very longvolcano. 22. Convergent plateboundaries occur wheretwo plates approach eachother. One result of two platesconverging is subduction. A deep oceanic trenchmarks the boundarybetween a subducting andan overriding plate at aconvergent boundary. 23. The movement of tectonic plates is related to the distribution ofheat by convection currents in the mantle. 24. Key Question: What will Earth look like in 50 millionsyears?*Read text section 28.2 BEFORE Investigation 28.2