Cosmogenic exposure dating and the pristine boulder fallacy(

Cosmogenic exposure dating of moraine boulders is a powerful method for learning about changes in glacier and ice sheet extents over time, but a commonly applied criterion for selecting samples in the field may yield incorrect results. In cosmogenic exposure dating, samples are collected from boulders resting on the crests of moraines. Under ideal conditions, the concentrations of rare nuclides in these samples will be proportional to the ages of the moraines, after correcting for nuclear decay. However, the estimated ages will be too young if the sampled boulders were originally covered by sediment, or if the boulders have lost material from their surfaces over time.