Biologists have long suspected that Greenland sharks were ancient animals, but it wasn't until a study published in August 2016 that we knew how old they really were. In the case of one Greenland shark, that turned out to be around 400 years. But without driver's licenses or tree rings to consult, how did the scientists know how old the animals were? The process was understandably tricky.
After collecting Greenland sharks that had died from becoming ensnared in fishing nets, the team examined the animals' eye lenses for carbon-14. Carbon-14 is an isotope that filled the atmosphere during the nuclear testing of the 1950s and has diminished at a predictable rate in the years since. This makes it a great marker for the year a cell came into being, since scientists just need to see how much carbon-14 is present, then find the year that quantity matches up with. Using this process, scientists determined that three of their smaller sharks had been born in 1963 or later. By combining that with the knowledge that newborn Greenland sharks are 42 cm (16.5 in) long, they were able to estimate how many centimeters per year the sharks grow, then correlate standard radiocarbon dating with the size of each shark to determine its age. The largest shark was 392, plus or minus 150 years. What's more surprising still is that the size of most pregnant females means that the animals must be at least 150 years old before they reach breeding age. Learn more about these ancient ocean dwellers with the videos below.