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Download Notes: The Theory of Plate Tectonics
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Transcript
Notes: The Theory of Plate Tectonics Plate Tectonics is a _________ developed in the late 1960s, to explain how the outer layers of the Earth ________ and __________. A theory was needed to explain why there are __________ prone areas, why ____________ eruptions occur only in specific areas, and why there are ocean __________ and ______________. Some Previous Ideas Expanding Earth idea…In the beginning the Earth’s _________ was evenly _________ over the ____________ ... but got stretched and thinned when the _________ expanded forming the ocean __________. But, ocean _________ are too wide to have formed by any reasonable __________. Contracting Earth idea…in the ____________ the Earth’s _________ was evenly spread over the _________ ... as the mantle ___________, the crust wrinkled forming ____________ and ocean ____________. But, wrinkles forming ____________ and ___________ should have formed more evenly rather than in _____________ bands. Geosynclines idea … weight of __________ dumped off the edge of the ___________ sinks the _________ down into the __________ ... eventually, it ___________ up to form _____________ ranges But, we see lots of ________ sinking down from the weight of __________, but can’t find any that are ___________. Law of ___________ says that if you don’t see it happening now, you can’t __________ it happened in the past. Theory of Continental Drift Developed by _________ __________ in the early 1900’s, it said that the ___________ are like rafts ____________ over the ___________ crust. Wegener suggested that throughout Earth’s ________ the continents have ________ and __________ numerous times. Wegener called the most recent unified landmass __________. It began to break apart about _______ million years ago. Wegener said that when ___________ ___________, ___________ ranges formed When ___________ separated or ___________, ocean __________ formed. Continental Drift Theory provided answers to some big mysteries. Like… The apparent ______________ fit of the ____________. This had been noticed since the early days of map-making. And … The presence of identical ________ on widely __________ continents belonging to organisms that could not have __________ the ocean or lived in the kind of __________ currently found in those locations. And …The presence of _________ tracks and deposits in areas that are, today, far too _________ for glaciers. The ___________ of the tracks were also problematic. But, Continental Drift Theory had its problems too. Like… Wegner was a ____________, who came up with his theory from watching _____ flows. This didn’t ________ the geologists. But the biggest problem was that Wegner couldn’t provide an ___________ for how the continents were able to _________ that made sense. He said the continents ________ due to the earth’s _________ … and ________ through oceanic crust like an ice-breaker plowing through ________. People said that Wegner cited no __________, only __________. This led some people to offer alternative ideas to ridicule ____________ Drift For example people noticed that a lot of the continents looked like _______ … suggesting that the __________ were dripping off ______________. Some geologist comments ... “Anyone who ________ his reputation for scientific sanity would _______ dare support such a __________.” "If we are to believe this __________, we must ________ everything we have learned in the last 70 years and start all over __________," __________ went back to his ice flows and _____ before seeing his ideas gain ___________. Plate Tectonics In the 1940’s _____________, Harry Hess, discovered a _______ down the ________ of the Atlantic __________ __________ analysis showed that the ________ of the ridge was very ______, like a long continuous ___________ Analysis of ________ taken from the ocean bottom also showed a symmetrical age pattern, ___________ in the middle, _________ at the edges Geologists knew that the direction of _________ _________ changed every million years or so. They also knew that when _________ cools, the __________ minerals record the direction of ____________ North. When they checked the ocean crust around the ________ they found that they recorded the _______ in long parallel stripes which corresponded to the historical _________ of magnetic North Geologists now had strong ___________ that new ________ was being __________ in the __________ of the Atlantic Ocean In fact, __________ is a volcanic island that sits right on _____ of the Mid-Atlantic Ridge. If new crust was being ________ at the center of the mid-ocean ridge, then somewhere else the old crust was being __________. Otherwise the earth would be getting larger and larger. Confirming this was that the age of the ocean crust around the world showed that none of it was older than ____ MY, less than a ___th of the age of the _______ continental crust. Something was eating up the crust! Oceanographers began to wonder about the long deep ________ they had also discovered in the oceans, particularly the __________. Often these trenches had _________ mountain chains along one side and had frequent _____________. Geologists discovered that __________ crust was being warped __________ into the __________ and being consumed at these ____________. As the ocean sediments and crust _________ the lighter elements would well _________ forming the volcanic ___________ chains behind the trench. These _________ formed a ring around the Pacific, characterized by ___________ and strong _____________ called the “________ ____ _______ ” With the discovery that ______ crust was being formed at Mid-Ocean ________ and _______ crust was being recycled at ________, Wegener’s ideas got a new lease on life. With this new knowledge scientists were able to understand the _______ that was _________ enough to ________ continents and how the different plate movements produced different __________! What makes the plates move? ___________ What makes the plates stop? Convection ______ ______. Or something ______ the _______ together How fast do plates move? The ________ ________ has the ________ rate (less than ______ cm/yr), and the ______ ________ _______ near Easter Island, in the South Pacific about 3,400 km west of Chile, has the _________ rate (more than ____ cm/yr). Geologists eventually discovered that Earth’s ______ was cracked into many _______, called _________, that are in constant _______ as a result of sea-floor spreading. Different kinds of plate interactions are responsible for ________, __________, and _____________. The solution to another _________ was suggested by the moving oceanic crusts. The __________ has many long chains of ___________ that seem to have been made one at a time in order. The ___________ chain is an example of one of these. The ________ chain extends far ________ the surface island. The Pacific island chains record the _________ of the Pacific plate over _________.