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New York State Earth Science June 2008 - Question 24 |
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Monday, 03 August 2009 10:09 |
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Correct Answer: Option 2 – Asthenosphere
The lithosphere (which includes the crust) is the outermost layer of the Earth and is cooler and more rigid than the layer below. The asthenosphere underneath is hot and flexible, transferring some of its heat through convection. In this case, the molten rock (magma) moves towards the cooler section, welling up through 100 km deep cracks in the lithosphere. When the two sides of the crack move apart, the cooled rock forms new tectonic plate material.
The plates ride on the asthenosphere, sometimes moving apart, sometimes past each other and other times moving together at plate boundaries. By using the global positioning system (GPS) over a period of years, the plates have been measured as moving from a few millimeters to up to 20 cm per year. Over many millions of years, this can mean thousands of kilometers of movement.
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Last Updated on Monday, 03 August 2009 10:35 |
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