Because they decay at different rates, the actual ratio of the two nuclides gradually diverges from the production ratio.Measuring this ratio tells you the length of time the sample has been buried.

As 10-Beryllium and 26-Aluminium preferentially build up in quartz, the aim of the first week was to crush down the samples and extract as pure quartz as we could.But there are other ways in which a rock can become exposed, as for example when a glacier erodes the sediment covering bedrock: when the glacier melts, the bedrock will be exposed.In the article on radiocarbon dating we have already introduced one cosmogenic isotope, Si and which has a half-life of 717,000 years.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. | 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.