How can scientists tell how old animals are?


For example, how do they know the Greenland shark is 512 years old (believed)?

In: Biology

Carbon dating is usually used in conjunction with other methods for a close estimate. All living organisms contain carbon-14, a radioactive isotope of carbon that comes from the sun’s rays interacting with the atmosphere and forming CO2 molecules which have a carbon-14 instead of a normal carbon-12. The CO2 is absorbed by plants for photosynthetis and animals eat the plants. When the organism dies it stops taking in the Carbon-14. The isotope slowly decays over time, following the exponential decay trend. By measuring the radioactivity of the fossil the scientists can tell how long it has been since the animal died

In living animals, age can be estimated off things like bone density/growth plate fusion, how worn teeth are, in animals like tortoises that have shells, the shells have rings like a tree so can be counted, general size of an animal, and extrapolation from known ages of other animals of similar type. Like if there’s a great white shark that’s 15 feet long and is known to be 30 years old, and was known to grow about 6 inches a year (all numbers hypothetical), and then another shark is seen that’s 25 feet long, an age can be estimated from the average.

For fish specifically, their age can be determined by counting growth rings in their bones. Bony fishes have a plate in their ear that makes a neat, concentric ring each year, like a tree. For sharks (which don’t have true bones) the vertebrae are used instead. Whale age can be determined by counting the layers in their earwax.