Beautifully patterned with white spots and stripes, the 60-foot-long whale shark is the largest—and one of the most striking—fish in the sea. Though it’s beloved by ecotourists and native to temperate oceans the world over, very little is known about these behemoths—including how long they live.

Recent investigations into other shark species have revealed astounding life-spans: The Greenland shark, for example, can live nearly 300 years, longer than any other vertebrate on Earth. (Many more sharks, such as the great white, near the 100-year mark.)

Those discoveries are largely because of advanced methods for determining a shark’s age, such as tracing carbon-14, a rare type of radioactive isotope that is a byproduct of Cold War-era bomb detonations,