A whale lays down earwax in alternating light and dark layers for its entire life and never sheds it. Researchers who split a plug lengthwise can read cortisol, testosterone, mercury and pesticide levels six months at a time, from birth to death, in animals that died decades before anyone thought to look.

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siliconcanals.com/k-a-whale-lays-down-earwax-in-alternating-light-and-dark-layers-for-its-entire-life-and-never-sheds-it-researchers-who-split-a-plug-lengthwise-can-read-cortisol-testosterone-mercury-and-pesticide-lev/