The age of sharks and the experiments on the Cold War bombs may not seem related. However, a recent study, published Monday in the Frontiers in Marine Science journal has unveiled an actual link between the two topics.
Sharks lack bony structures called otoliths that are used to assess the age of other fish. However, a type known as Whale shark vertebrae feature distinct bands - a little like the rings of a tree trunk - and it was known that these increased in number as the animal grew older. However, former studies didn't have a unified understanding on the issue. Some suggested that a new ring was formed every year, while others concluded that it happened every six months.
To resolve the question, an international team including researchers from Rutgers University in New Jersey, USA, the University of Iceland, and the Australian Institute of Marine Science, Western Australia, turned to the radioactive legacy of the Cold War's nuclear arms race.
During the 1950s and 1960s, the USA, the Soviet Union, Great Britain, France, and China conducted tests of nuclear weapons. Many of these were explosions detonated several kilometers in the air. One powerful result of the blasts was the temporary atmospheric doubling of an isotope called carbon-14.
Carbon-14 is a naturally occurring radioactive element that is often used by archaeologists and historians. Its rate of decay is constant and easily measured, making it ideal for providing age estimates for anything over 300 years old.
However, it is also a by-product of nuclear explosions that saturated the air, and then the oceans. The isotope gradually moved through food webs into every living thing on the planet, producing an elevated carbon-14 label.
In a report published by the Australian Institute of Marine Science, Dr. Mark Meekan said: "This additional radioisotope also decays at a steady rate, meaning that the amount contained in bone formed at one point in time will be slightly greater than that contained in otherwise identical bone formed more recently."
