Comment: 22:34 - 23:33 (00:59)
Source: Annenberg/CPB Resources - Earth Revealed - 18. Metamorphic Rocks
Keywords: "John Rosenfeld", metamorphism, "United States", "snowball garnet", orogeny, "Appalachian Mountains", "rubidium isotope decay", geologist, crystal, Vermont, "geologic time", humans, tree
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Our transcription: In the metamorphic regions of the northeastern United States, for example, snowball garnets preserve an important record of the building of the Appalachian Mountains.
By comparing the amount of rubidium isotope decay at the center of these garnets relative to their margins, geologists can determine how fast the crystals grow.
The garnets in Vermont took about ten, ten and a half million years to grow, and it's correspondent to a growth rate of roughly a few atomic diameters per year.
And to give you some comparison of what that might be in terms that might be more in a human reference frame, that corresponds to about a millionth as fast as the diameter of a ordinary tree might grow.
So it's a very slow process.
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Geology School Keywords
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