A few years ago, I was having coffee with an environmental chemist. I happened to mention an ancient method for determining a whale’s age: More than a century ago, whalers learned to examine the creatures’ earwax, which builds up over the years and congeals into a sticky plug. If you extract it from a deceased animal and cut the cylinder in half lengthwise, you’ll see light and dark rings. Researchers think the light bands could be from a buildup of lipids during summer feasting, while the dark ones come from winter fasting. Count the rings, and you can estimate the animal’s age. Then an idea came to us: The circles give clues about nutrition, so what else could they reveal?