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USGS CMG InfoBank: Glacial Evidence In Geology

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Comment: 01:38 - 02:33 (00:55)
Source: Annenberg/CPB Resources - Earth Revealed 23. Glaciers
Keywords: "James Sadd", glacier, geologist, "Louis Agassi", Europe, sediment, boulder, "glacial advance", "glacial retreat", "sedimentary rock", continent, "Northern Hemisphere", "glacial ice", "landscape evolution", "glacial melt"

Our transcription: Early scientists didn't really appreciate the important geological role of glaciers.
Even geologists were convinced that glaciers had never existed outside of their present locations over the last one million years.
A breakthrough came in 1836 when Swiss scientist, Louis Agassi, reported evidence that the inhabitance of medieval villages in Europe had moved their towns to keep pace with advancing glaciers.
Further study revealed that glaciers leave behind a distinctive deposit of sediment like these boulders as they melt back and retreat.
Geologically recent examples of these sedimentary deposits, found hundreds of kilometers from the nearest glacier, demonstrated to Agassi that vast portions of the continents of the Northern Hemisphere had been recently covered with glacial ice.
Observations like these led to the realization that glaciers are active and powerful agents of landscape evolution.

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