The half-life of this hydrophilic nonreactive isotope makes it suitable for dating in the range of 60,000 to 1 million years.
Additionally, large amounts of Cl has seen use in other areas of the geological sciences, including dating ice and sediments (Nishiizumi et al., 1983; Phillips et al.,1983).
By sampling the rocks and separating certain minerals (such as quartz or pyroxene) and calculating the amount of these minerals (as a ratio to other, stable, minerals), we can work out how long the rock has been exposed on the earth’s surface.
Cosmogenic nuclides are rare nuclides that form in surface rocks because of bombardment by high-energy cosmic rays.
This analysis relies on the fact that lighter masses are accelerated to slightly higher velocities than heavier ones, so that after traversing a distance of a metre or so, they arrive at the detector a few nanoseconds earlier. Extremely large variations of atmospheric Bentley, H.
Hence Be abundances in these cores are better correlated with climatic variations than with past variations in geomagnetic field intensity (e.g. This result caused considerable puzzlement at the time, but is not really surprising since the cosmogenic isotope flux in polar snow is largely of local (polar) origin, where cosmic-ray intensity is not significantly shielded by the Earths magnetic field.
Cartoon illustrating cosmogenic nuclide exposure ages. A glacier transports an erratic boulder, and then recedes, exposing it to cosmic rays.
Spallation reactions occur in minerals in the rocks upon bombardment by cosmic rays.
This long period of applicability is an added advantage of cosmogenic nuclide dating.Radiometric dating--the process of determining the age of rocks from the decay of their radioactive elements--has been in widespread use for over half a century.There are over forty such techniques, each using a different radioactive element or a different way of measuring them. | 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. Wiens has a Ph D in Physics, with a minor in Geology.His Ph D thesis was on isotope ratios in meteorites, including surface exposure dating.The addition of Cl can be evaluated by measurement of the Cl and other ionic concentrations in the water, in-situ production can be estimated after a measurement of aquifer U and Th concentrations, and precipitation input values can be estimated using present-day local values.For the determination of water transit times between two sampling locations instead of the absolute age of the water, the value measured at the upgradient location is used as the input value.Cl, like Li and B, has two stable isotopes (Cl might be a useful tool for hydrograph separation analysis and determination of mixing between regional and shallow ground water mixing (Nimz, 1998).A multi-isotopic approach is almost always beneficial ("the more isotopes the merrier! One recent example is the use the Cl of chlorinated solvents such as TCE and BTEX to identify the sources of the contaminants in ground water, and the degradation reactions that may remediate the pollution plumes.