He has had some exposure to squares, but he doesn't know exponents.

He only needs to understand the data. That's why I'm currently leaning towards just giving examples. He will be making a seismograph, so he'll have an understanding of the difference between a magnitude 4 quake (which I'm guessing will be bumping the table lightly) and a magnitude 8 quake (really banging the table around?). But I want him to be able to explain how it's expressed with the Richter scale.