Cosmogenic surface exposure dating

The most commonly used "cosmogenic isotopes" are radionuclides (He, require far less labor intensive purification and a simple sector-field mass spectrometer.Thus cosmogenic noble gases offer the advantage of faster and less expensive data acquisition.Super high energy particles—mostly protons— are produced by our Sun, supernovae, and probably other extraterrestrial sources.These particles continuously enter the Earth system at incredible rates and are often, but misleadingly, called cosmic rays.If we are particularly interested in the timing of the uncovering of a surface—say, bedrock that had been covered by ice, or sediments that had been revealed by the incision of a stream—we can employ cosmogenic nuclide surface exposure dating to study that uncovering process.This is different from techniques (like Ar, or U/Th) that date the formation of a rock itself.Radiocarbon dating is abundantly used and offers very high precision dates, but we often want to date an event that is either too far in the past, or without the right type of organic matter, to be dated by C.While there is a slew of other dating techniques to choose from, cosmogenic nuclide exposure dating is useful for relatively young (~100 to 10 million years old) samples.

Those particles continue traveling toward the Earth’s surface, likely colliding with additional atoms on the way.Surface exposure dating provides critical information on a range of Earth science problems including ages of glacial features, erosion rates, and rates of fault motion.The technique relies on the production of rare isotopes produced by interactions of cosmic rays with target nuclei in rocks within ~ 1 meter of Earth's surface.However cosmogenic He dating of additional minerals which are known to retain He at Earth surface conditions, especially the common accessory phases apatite, sphene, and zircon.Upon entering the Earth’s surface, these high-energy particles quickly collide with the relatively dense assortment of atoms around, breaking apart more atoms in the upper ~2 meters of a rock (or other) surface but failing to reach much deeper than that.

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Depending on the elements that a particle collides with, it produces different end products.

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