The study tracked changes in the sun by looking at previous solar cycles of change, such as Cycle 22 which lasted from the years 1986 to 1996, and found that the oscillation frequencies were confined to a thinner layerthan those previous cycles.
That was more than 20 years ago... He says his predecessors had accumulated light technologies one after another, in the same way that each stratum of earth stacks one layer atop the previous.