When radiometric decay occurs, one of the byproducts is free Helium. An expectation for those who believe in long ages is that the atmosphere should have a great deal of Helium since they would expect the process of radiometric decay to have been happening for 4.5 billion years. However, there is only .04% of this expected Helium in the atmosphere. Totally unexpected for those who believe in deep time is that the Helium never entered the atmosphere in the first place. It is still trapped in Zircons and other crystalline structures in the crust and mantle. This is unexpected from their point of view, because Helium easily escapes through cracks and openings over time. But since there was not deep time, as they expect, a great deal of radioactive decay has happened in a short time. To read further details on this topic, click here.