Cosmogenic exposure dating
In one kilogram of soil, the potassium-40 amounts to an average 370 Bq of radiation, with a typical range of 100–700 Bq; the others each contribute some 25 Bq, with typical ranges of 10–50 Bq (7–50 Bq for the It is well known that some plants, called hyperaccumulators, are able to absorb and concentrate metals within their tissues; iodine was first isolated from seaweed in France, which suggests that seaweed is an iodine hyperaccumulator.Synthetic radioisotopes also can be detected in silt.Theoretically, exposures of surfaces from between a few thousand to about 10 million years old can be dated by the measurement of the Be-10 and Al-26 isotopes.Surface exposure dating is a collection of geochronological techniques for estimating the length of time that a rock has been exposed at or near Earth's surface.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.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.
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.
| Using cosmogenic nuclides in glacial geology | Sampling strategies cosmogenic nuclide dating | Difficulties in cosmogenic nuclide dating | Calculating an exposure age | Further Reading | References | Comments | Cosmogenic nuclide dating can be used to determine rates of ice-sheet thinning and recession, the ages of moraines, and the age of glacially eroded bedrock surfaces.
Cosmogenic nuclide dating uses the interactions between cosmic rays and nuclides in glacially transported boulders or glacially eroded bedrock to provide age estimates for rock at the Earth’s surface.
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.
Some cosmic ray particles reach the surface of the earth and contribute to the natural background radiation environment.
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Surface exposure age dating requires intensive chemistry.