Boulders the size footballs could help scientists predict the West Antarctic Ice Sheet’s contribution to sea-level rise according to new research in Geology. Initial results show that Pine Island Glacier has ‘thinned’ by around 4 centimeters per year over the past 5,000 years, while Smith and Pope Glaciers thinned by just over 2 cm per year during the past 14,500 years. These rates are more than 20 times slower than recent changes: satellite, airborne and ground based observations made since the 1990s show that Pine Island Glacier has thinned by around 1.6 meters per year in recent years. The scientists reached their conclusions by investigating how long the boulders have been exposed to cosmic radiation rather than being shielded by ice or sediment.