The method sidesteps the problem that Greenland sharks have no calcified structures to count growth bands in. The lens nucleus is metabolically inert from the embryo onward, so its carbon carries the atmospheric signature of the year the shark was conceived. Nuclear weapons testing in the 1950s spiked atmospheric carbon-14, and lenses bearing that bomb pulse identify sharks born after roughly 1960, anchoring the calibration for older animals.
The 2016 study of 28 females gave a most likely mean maximum around 390 years, with wide confidence bounds, and estimated that females do not mature until about 150 years old.
The uncertainty is genuine and often dropped in retellings. The published range for the oldest individual spans roughly 272 to 512 years, and no single shark has a precise age. The extremely late maturity matters for management: a species that takes a century and a half to breed cannot absorb fishing mortality, and it is now listed as Vulnerable.