Cold War nuclear test residue offers a clue to whale sharks’ ages
Radioactive residue from Cold War nuclear tests has given scientists a cipher to decode the ages of whale sharks, written on the animals’ vertebrae. Whale sharks (Rhincodon typus) accumulate alternating stripes of opaque and translucent tissue on their vertebrae as they age, similar to the way tree trunks grow rings. But until now, scientists haven’t known whether whale shark vertebrae gain a new growth band each year or every six months — making it difficult to gauge just how fast these sharks grow or how long they live. New measurements of carbon-14 in the vertebrae of two whale sharks that lived during the 20th century suggest that growth bands form annually, researchers report in the April 2020 Frontiers in Marine Science. Soviet and American nuclear weapons tests in the 1950s and 1960s produced that carbon-14, which built up in Earth’s atmosphere and oceans. By matching the amount of carbon-14 in different vertebral growth bands with the known carbon-14 levels in surface seawater in different...