Beryllium dating

GlacierBeryllium dating is used to estimate the time a rock has been exposed on the surface of the Earth, as well as erosion and sedimentation rates.

Beryllium-10 is another cosmogenic nuclide. Like carbon-14, most of it is formed in the earth’s upper atmosphere. After formation, beryllium-10 binds to atmospheric dust particles or dissolves in atmospheric water vapor. It is transported to earth surface in rain so consequently it has a much shorter atmospheric residence time than carbon-14. It accumulates on the earth’s surface and depending upon the sedimentation regime in the local environment, it can be used to date surface accumulation rates, surface erosion rates, or for dating layers within ice cores. Its half-life is 1.39 million years.

Vanishingly small amounts of beryllium-10, carbon-14 and aluminum-26 are also created at the earth’s surface. The creation occurs within minerals the upper meter of rocks exposed directly to the sky. If rocks are undisturbed for millennia, differences in the cosmogenic isotope content of the upper and lower surfaces accumulate. These differences can be translated into a measure of time since the rocks were either first exposed to sunlight, or covered over and isolated from the cosmic ray flux. These reactions are more frequent at high altitudes, where surface cosmic ray fluxes are higher.

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