Highly read on wiley.com in March 2013
Rare isotopes generated by cosmic rays can reveal the timing of events such as megafloods and rock debris flows.
Analysis of the isotopes' concentrations can help researchers to estimate a rock's age, a method known as cosmogenic dating. Benjamin Mackey and Michael Lamb at the California Institute of Technology in Pasadena extended this technique to show how boulders move and erode. They modelled the accumulation of these isotopes in boulders and found that the isotopes' distribution near the surface indicates how often a metre-plus sized rock has been transported.
Because boulders are often used to date landforms, such information provides clues about geological events and the creation of features such as glaciers and shorelines.