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| | Inside the Earth [This Dynamic Earth, USGS] (Site not responding. Last check: 2007-11-06) |
 | | The crust, the outermost layer, is rigid and very thin compared with the other two. |
 | | The thickness of the crust beneath continents is much more variable but averages about 30 km; under large mountain ranges, such as the Alps or the Sierra Nevada, however, the base of the crust can be as deep as 100 km. |
 | | Below the crust is the mantle, a dense, hot layer of semi-solid rock approximately 2,900 km thick. |
| pubs.usgs.gov /gip/dynamic/inside.html (485 words) |
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