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The cumulative flux of cosmic rays at a particular location can be affected by several factors, including elevation, geomagnetic latitude, the varying intensity of the Earth's magnetic field, solar winds, and atmospheric shielding due to air pressure variations.Rates of nuclide production must be estimated in order to date a rock sample.Using certain cosmogenic radionuclides, scientists can date how long a particular surface has been exposed, how long a certain piece of material has been buried, or how quickly a location or drainage basin is eroding.
This isotope may be produced by cosmic ray spallation of calcium or potassium.
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.
Researchers suggested that the accumulation of these isotopes within a rock surface could be used to establish how long that surface was exposed to the atmosphere.
Many of these electrically charged particles never reach our planet because they are deflected back into space by the Earth’s magnetic field (see Equation 3.3).
The degree of ‘protection’ provided by the magnetic field is greater at low latitudes (where the magnetic field lines run parallel to the surface) than at the poles (where they are perpendicular to the surface).
Surface exposure dating is used to date glacial advances and retreats, erosion history, lava flows, meteorite impacts, rock slides, fault scarps, cave development, and other geological events.