There is a clock hidden in each halo. That is what makes Gentry's discovery so important. We can actually know how long it took for each halo to form. Henderson studies the halos. G.H. Henderson, in eastern Canada, studied the halos for ten years in the 1930s.
Gentry becomes interested.
Robert Gentry wanted to do his doctoral research on radioactive halos, but was refused permission because such research might conflict with evolutionary theories about the age of the earth. So he went to Nova Scotia and examined Henderson's slide collection. After a third refusal by Georgia Tech, Gentry dropped out of school and began studying the halos on his own. Eventually, he was able to obtain a position at Oak Ridge National Laboratory, in northeastern Tennessee. He used its multimillion dollar facilities for over a decade.