As whales go through their annual cycles of summer binge-eating and winter migrations, the wax in their ears changes from light to dark. These changes manifest as alternating bands, which you can see if you slice through the plugs. Much as with tree rings, you can count the bands to estimate a whale’s age. And you can also analyze them to measure the substances that were coursing through the whale’s body when each band was formed. A whale’s earwax, then, is a chronological chemical biography.
Stephen Trumble and Sascha Usenko from Baylor University have worked out how to read those biographies. And they’ve shown that whale earwax not only reveals the lives of their owners, but the history of the oceans. Hunting, abnormal temperatures, pollutants—it’s all there. If all of humanity’s archives were to disappear, Trumble and Usenko could still reconstruct a pretty decent record of whaling intensity by measuring the stress hormones in the earwax of a few dozen whales.