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Calculating age of Whale sharks using Atomic bomb dating

Date: 12 April 2020 Tags: Biodiversity

Issue

Researchers have measured the carbon-14 isotope in the cartilaginous vertebrae of two whale sharks and correlated it to the carbon-14 patterns created by Cold War–era bomb detonations in order to estimate their age.

 

Background

Whale sharks are the largest fish in the ocean and one of the longest lived. Sharks lack otoliths, bony structures in the skull that scientists use to estimate the age of most fish, which makes it tricky to estimate their age.

 

Details

  • It was already known that these bands/patterns existed and increased in number as a shark aged. But it was unclear whether new rings appeared yearly or every six months.

  • The researchers compared carbon-14 levels in the rings to data on fluctuations in its global presence during the busy years of atmospheric nuclear tests in the 1950s and 1960s.

  • Previous methods, such as estimating their age by comparing an individual’s length at different times using photographs, have estimated that whale sharks live up to 130 years, but bomb dating is the most accurate method yet.

  • The results are important to understand the growth rate and longevity of whale sharks, which is key to conservation and management efforts of this endangered species.

  • Whale sharks are filter feeders, swimming great distances through the world's tropical oceans to find enough plankton to sustain themselves. They have a brownish-grayish color on the back and sides with white spots, with a white underside.

 

Carbon-14 dating

  • Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon.

  • It is based on the fact that radiocarbon (C) is constantly being created in the atmosphere by the interaction of cosmic rays with atmospheric nitrogen.

  • The resulting 14C combines with atmospheric oxygen to form radioactive carbon dioxide, which is incorporated into plants by photosynthesis; animals then acquire 14C by eating the plants.

  • When the animal or plant dies, it stops exchanging carbon with its environment, and thereafter the amount of 14C it contains begins to decrease as the 14C undergoes radioactive decay.

  • Measuring the amount of 14C in a sample from a dead plant or animal, such as a piece of wood or a fragment of bone, provides information that can be used to calculate when the animal or plant died.

  • The older a sample is, the less 14C there is to be detected, and because the half-life of 14C (the period of time after which half of a given sample will have decayed) is about  5,730 years, the oldest dates that can be reliably measured by this process date to around 50,000 years ago.

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