If the giant ice balls found in Spain, called megacryometeors, are really just enormous hailstones, the updrafts would have to be very strong and a result of a violent storm. However, these megacryometeors fell from cloudless skies. The cause of the giant hailstones is unclear but scientists from the University of Valencia say damage to the ozone layer could be to blame. This layer of gases protects us from solar radiation, but on the days preceding the event, ozone levels were unusually low in the stratosphere. As a result, less solar radiation was absorbed by the stratosphere, allowing more heat to pass through to the stroposphere and resulting in a cooler stratosphere. This may have caused turbulent wind conditions at the tropopause, the boundary between these two layers of the atmosphere. Subsequently, passing planes could have deposited charged ions which acted as nuclei for the formation of hailstones which grew as they cycled up and down. The only problem with this theory is that it doesn't explain why these hailstones were so big, and the mystery remains unsolved.