Radionuclide dating - wireless says validating identity
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.
Wherever we are on Earth, when we are outside, we are constantly bombarded by these cosmic rays.
| 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.
It is an excellent way of directly dating glaciated regions.
It is particularly useful in Antarctica, because of a number of factors: Cosmogenic nuclide dating is effective over short to long timescales (1,000-10,000,000 years), depending on which isotope you are dating.
When particular isotopes in rock crystals are bombarded by these energetic cosmic rays neutrons, a reaction results.
Spallation reactions are those where cosmic-ray neutrons collide with particular elements in surface rocks, resulting in a reaction that is sufficiently energetic to fragment the target nucleus. Counting the numbers of these isotopes, normally as a ratio to other isotopes, means that scientists can calculate how long rocks have been exposed at the Earth’s surface.
These cosmic rays do not penetrate deep into the earth’s surface.
Different isotopes are used for different lengths of times.
This long period of applicability is an added advantage of cosmogenic nuclide dating.
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.