Radionuclide dating

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Thus, one can date strata overlying buried paleosols by measuring Be at multiple depths in the paleosol and calculating the burial age of the paleosol from the resulting isochron.

We focus on applying this approach to till-paleosol sequences, but the basic idea of forming an Be burial isochron with a set of samples that share the same burial age, but differ in other aspects of their exposure history, applies to other stratigraphic settings as well.

These cosmic rays do not penetrate deep into the earth’s surface.

This is important for glacial geologists, as it means that surfaces that have had repeated glaciations with repeated periods of exposure to cosmic rays can still be dated, as long as they have had sufficient glacial erosion to remove any inherited signal.

By sampling the rocks and separating certain minerals (such as quartz or pyroxene) and calculating the amount of these minerals (as a ratio to other, stable, minerals), we can work out how long the rock has been exposed on the earth’s surface.

Cosmogenic nuclides are rare nuclides that form in surface rocks because of bombardment by high-energy cosmic rays[3].

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A buried paleosol implies a period of surface exposure and nuclide accumulation, followed by burial and a halt to nuclide production.Some cosmic ray particles reach the surface of the earth and contribute to the natural background radiation environment.It was discovered about a decade ago that cosmic ray interaction with silica and oxygen in quartz produced measurable amounts of the isotopes Beryllium-10 and Aluminium-26.When particular isotopes in rock crystals are bombarded by these energetic cosmic rays neutrons, a reaction results.Spallation reactions are those where cosmic-ray neutrons collide with particular elements in surface rocks, resulting in a reaction that is sufficiently energetic to fragment the target nucleus[3]. Counting the numbers of these isotopes, normally as a ratio to other isotopes, means that scientists can calculate how long rocks have been exposed at the Earth’s surface.

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