Last week, we shared with you how we use carbon to help us date the rocks. This week, Dr. Derek Fabel is sharing how we do something similar with Beryllium and Aluminum:
Because we know at what rate our isotopes, like Beryllium and Aluminum, are produced within the quartz when it is exposed at the surface of the Earth we have a ‘clock’. By measuring the concentration of isotopes in quartz we can determine how long the quartz has been exposed at the surface of the Earth.
MAGIC-DML uses this ‘clock’ to determine when nunataks have become exposed from under the East Antarctic ice sheet. At its simplest, a few tens of meters of ice shields rocks from cosmic rays. When the ice disappears the ‘clock’ in the rocks starts ticking. During our two Antarctic field seasons we collected rock samples containing quartz from the slopes of nunataks at different elevations above the present day ice surface. If the ice sheet surface was higher in the past we expect that samples collected from a greater elevation above the ice will have been exposed longer than lower elevation samples, and that the exposure age of the samples will inform us about when the ice sheet surface lowered and by how much.
You can also think of it like sand in an hourglass. When I look at an hourglass, I can tell how much time has passed by seeing how much sand has fallen to the bottom bowl. In a similar way, we can tell how much time has passed since our rocks came to the surface by looking at how isotope is within them!
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