Submitted by Tim Spuck on Tue, 03/20/2012 - 19:36


Can you explain what is meant by cosmogenic exposure dating and how it is used to determine how long ago a glacier retreated?

Thanks, Tim

Amber Lancaster

Absolutely. When certain molecules are exposed to light, they actuallystart to decay due to the exposure to radiation from the sun. Before
light hits them, they are pretty stable and when the rocks are
underneath the glacier, the light isn't able to get to them. Once the
glacier retreats, the radioactive decay starts to happen. There are a
few different isotopes that are measured, but the most common one is
Beryllium-10. This is the isotope that is formed once the sun hits the
mineral. Geologists take samples of rocks and measure the amount of
Beryllium-10 found in the rock. The more Beryllium-10 found in the
rock, the longer it has been exposed to the sun. Does that help? :)

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