Cosmogenic surface exposure dating

When one of these particles strikes an atom it can dislodge one or more protons and/or neutrons from that atom, producing a different element or a different isotope of the original element.

In rock and other materials of similar density, most of the cosmic ray flux is absorbed within the first meter of exposed material in reactions that produce new isotopes called cosmogenic nuclides.

So-called ‘inherited’ Be from earlier exposure invalidate a single age determination, but there are ways to check for ‘prior exposure’ for example by measurement on another cosmogenic isotope, utilising the difference in half-lives.

SED is now an established tool for geomorphology and landscape change studies.

Cosmogenic isotopes are created when elements in the atmosphere or earth are bombarded by high energy particles (-mesons and protons, collectively known as cosmic rays) that penetrate into the atmosphere from outer space.

Frequently, erosion, exhumation and boulder toppling are blamed for the younger outliers.

Assuming a constant rate of production, the number of atoms of Be-10 and Al-26 that accumulate in a rock surface will be proportional to the length of time the rocks were exposed to cosmic ray bombardment and the respective rates of radioactive decay for each isotope.

An age determined by measurement of the amount of each nuclide would be an estimate of the age of the surface exposure, that is, the surface could have been exposed for much longer than the minimum calculated age.

The most common of these dating techniques is Cosmogenic radionuclide dating.

Earth is constantly bombarded with primary cosmic rays, high energy charged particles — mostly protons and alpha particles.

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