Cosmogenic isotope dating
In the article on radiocarbon dating we have already introduced one cosmogenic isotope, Si and which has a half-life of 717,000 years.
Because the isotopes we're using have a short half-life, it follows that if a rock has been buried for a few million years the quantities of these isotopes will be negligible.
The ages are uncorrected for temporal variations in production rates and may underestimate the true ages by 5–7%.
The former age, although implying early deglaciation for this area of the British ice sheet, is not incompatible with minimum deglaciation ages from other contexts and locations in northwest England.
Peter was an innovative researcher whose considerable insights made this particular work possible.
It is an excellent way of directly dating glaciated regions.
Cl) surface exposure dating of four of the erratic boulders at Norber in the Yorkshire Dales National Park, northwest England, yielded mean ages of ∼22.2 ± 2.0 ka BP and ∼18.0 ± 1.6 ka BP for their emplacement.
These two mean values derive from different Cl production rates used for exposure age calculation.
Be production rate is carefully calibrated, for example by correcting for partial attenuation and complete shielding effects.
Also, the exposure assumptions must be justified through other means, for example by taking into account clear signs of surface erosion and information consistent with (or suggestive of) 100% shielding prior the exposure event to be dated.