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Scientists estimate a Greenland shark’s age by measuring radiocarbon (¹⁴C) in the nucleus at the center of its eye lens. That nucleus forms before birth and contains metabolically inert proteins, so it preserves a carbon signal from the animal’s prenatal development. Researchers compare that signal with marine radiocarbon chronologies, including the atmospheric nuclear-test “bomb pulse,” and calculate an age range.
The result is an estimate, not a precise birthday. The landmark 2016 study estimated that a 502-centimeter female was 392 years old, with a 95.4% probability range of about 272 to 512 years. The estimate has not been independently validated, and uncertain deep-ocean carbon history makes the range wide.
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Why scientists cannot simply count a Greenland shark’s growth rings
Many fish can be aged by counting repeated growth bands in hard tissues such as otoliths, scales, fin spines or vertebrae. Greenland sharks are unusually difficult to treat this way. They lack fin spines, and their vertebrae are too soft or poorly calcified to provide consistently readable bands.
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Body length is not a reliable substitute for age either. A large shark is likely older than a small one, but growth varies among individuals and does not provide a calibrated year-by-year record. To estimate age, researchers therefore needed a tissue that records a date when it forms and then stops changing.
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The eye-lens nucleus preserves a birth-time signal
The central part of the eye lens is called the embryonic nucleus. In vertebrates, its crystalline proteins form during prenatal development. Once formed, those proteins are metabolically inert: unlike most tissues, they do not continually exchange their carbon with the environment.
That makes the nucleus a biological time capsule. Its radiocarbon reflects the carbon available to the mother and her food web around the period when the embryo was developing. If researchers can relate that carbon signature to a dated marine chronology, they can estimate when the shark was born.
The method does not read an age printed inside the lens. It infers a birth date from the chemical composition of a tiny tissue sample and then reports the resulting age as a probability distribution.
How the radiocarbon method works
1. Obtain an eye lens from a captured specimen
The 2016 study analyzed lens nuclei from 28 female Greenland sharks collected during scientific surveys in Greenland between 2010 and 2013. The animals ranged from 81 to 502 centimeters in length. This is a specimen-based laboratory method, not a routine, non-invasive test that can be performed on a free-swimming shark.
2. Isolate the embryonic nucleus
Researchers remove the lens and target its central embryonic region rather than treating the whole lens as one uniform sample. The center is the portion formed before birth and protected from later metabolic replacement, which is why it can retain an original carbon signal for centuries.
3. Measure radiocarbon and stable isotopes
The laboratory measures ¹⁴C in the nucleus. It also examines stable carbon and nitrogen isotopes. Those additional measurements help evaluate where the embryonic carbon came from, because the signal reflects the mother’s diet and the surrounding marine food web rather than a simple direct reading of atmospheric carbon.
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4. Compare the result with marine chronologies
The measured value is compared with records of how radiocarbon has changed through time in the ocean. The comparison must account for marine carbon that can be older than surface atmospheric carbon and for regional differences in how quickly carbon moves through the ocean.
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Atmospheric nuclear-weapons testing beginning in the mid-1950s released extra radiocarbon into the environment. The resulting increase, known as the bomb pulse, is a recognizable time marker. It is especially useful for animals born after that signal entered marine food webs.
6. Convert the match into an age range
For each shark, the radiocarbon measurement and the chronology are combined in a model. The output is an estimated birth period and an uncertainty range. Researchers then relate that estimated birth period to the date of capture to obtain an approximate age.
What the 2016 study actually estimated
The study by Julius Nielsen and colleagues, published in Science on 12 August 2016, produced several widely quoted numbers. Each is a statistical estimate rather than a directly observed age.
| Quantity | Study result | How to read it |
|---|---|---|
| Sample | 28 female sharks, 81–502 cm long | The original dataset covered females collected on Greenland scientific surveys from 2010–2013; it did not directly age males or every Greenland shark population. |
| Estimated minimum lifespan | At least 272 years | This is the study’s lower-bound conclusion about longevity, not the measured age of one identified shark. |
| Estimated age at sexual maturity | 156 ± 22 years | The study reported this with a 95.4% probability range; it is a model-based estimate for when sexual maturity is reached. |
| Largest sampled animal | 392 ± 120 years | The shark was a 502 cm female. The reported 95.4% probability range extends approximately from 272 to 512 years. |
NOAA’s public explanation summarizes the same result as an estimated 272–512 years for the roughly five-meter female and emphasizes that carbon dating provides estimates, not definitive ages. Saying that scientists “proved” the shark was exactly 392 or 400 years old overstates what the method can establish.
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Why the bomb pulse helps—and why it does not solve every case
The bomb pulse provides a dated feature against which a radiocarbon measurement can be aligned. In the study, only the smallest sharks, those 220 centimeters or shorter, showed signs of the bomb-pulse signal. Their radiocarbon values could therefore be associated with the period after atmospheric testing began, giving the model a relatively strong time marker.
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Larger sharks appeared to predate the bomb pulse. For them, the researchers had to infer birth dates from older marine chronologies and assumptions about how radiocarbon moved through the deep ocean. That makes the resulting ages more dependent on the model and less tightly anchored to a single, easily recognized event.
How accurate is a Greenland shark age estimate?
The estimate is useful for understanding extraordinary longevity, but it is not precise in the way a known hatch date would be. The 392-year figure carries an uncertainty of ±120 years at the study’s reported 95.4% probability level. In practical terms, the likely interval is broad enough to include sharks that are roughly 272 years old and others more than five centuries old.
The main uncertainty is not simply laboratory measurement error. It comes from the history of radiocarbon in the deep ocean before and after nuclear testing. Deep water can contain carbon that has circulated for a long time, and the timing and magnitude of that reservoir effect are not known well enough to assign an exact birth year to an old shark.
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What “392 ± 120 years” means statistically
The notation should be read as a central estimate plus a wide uncertainty extent, not as a claim that the shark’s true age was somewhere within 120 years of 392 with certainty in every possible interpretation. The study’s stated 95.4% probability range is the relevant qualification: under the model and assumptions used, the estimated age distribution spans approximately 272–512 years.
A probability range also explains why the often-repeated phrase “400-year-old shark” is misleading when presented as a fact. It is a rounded description of a model output, not a calendar age verified by an independent marker.
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What the isotope measurements reveal about the mother’s diet
The embryonic lens nucleus records carbon obtained through the mother’s food web. Stable carbon and nitrogen isotope measurements help researchers assess that source and check whether the radiocarbon signal is consistent with the ecological pathway feeding the developing embryo.
This matters because an ocean animal does not receive carbon in exactly the same way as an atmospheric sample. Carbon passes through seawater, plankton and prey, and different marine regions can have different radiocarbon histories. Accounting for the food web helps prevent the lens value from being treated as though it were a direct measurement of the atmosphere on a known date.
What animals and populations the evidence covers
The original sample consisted entirely of females caught in Greenland waters during surveys from 2010 through 2013. The findings therefore support an age-estimation method for tissue from captured Greenland sharks, but they do not demonstrate that males have identical age distributions, that every population follows the same growth pattern, or that a living shark can be aged from an external scan.
The method also depends on obtaining the lens nucleus. It is not equivalent to attaching a tag, photographing a shark or measuring its length. A routine live-animal test has not been established by the evidence described here.
Is there a second validated method for Greenland sharks?
No independent method has been validated for this species in the current official assessment. Conventional growth-band approaches are unavailable or unreliable because of the shark’s anatomy, and the radiocarbon study remains the sole published aging investigation identified by COSEWIC’s 2025 review.
That does not make radiocarbon analysis useless. It means the result should be reported with its assumptions and uncertainty rather than treated as an independently confirmed age. A genuine comparison would require another method that measures a different biological feature and has its own demonstrated relationship to calendar age.
Why the result still matters despite the uncertainty
Even a broad estimate changes how scientists understand Greenland sharks. A lower bound of at least 272 years places the species among the longest-lived vertebrates known. The estimated age at sexual maturity, 156 ± 22 years, also implies an exceptionally long delay before reproduction compared with most fishes.
Those characteristics affect conservation decisions. A population whose members mature only after many decades cannot quickly replace adults lost to fishing or other mortality. The exact age of any one shark remains uncertain, but the combination of the lens evidence, longevity estimates and delayed maturity indicates a life history that is unusually slow.
What would make future ages more reliable?
Improving confidence would require evidence that addresses the known weaknesses of the current estimate:
- Better regional marine radiocarbon chronologies, especially for the deep waters inhabited by older sharks.
- More samples from different locations, size classes and both sexes to test whether the Greenland sample represents the species broadly.
- Independent validation using a separate biological or geological time marker, if scientists can identify one that works for this species.
- Models that make the food-web pathway and ocean reservoir effects more explicit rather than assuming a single marine history.
Until such evidence exists, the scientifically responsible wording is “radiocarbon-estimated age” followed by the uncertainty range and the assumptions behind it.
The bottom line on Greenland shark age
Scientists estimate a Greenland shark’s age from ¹⁴C preserved in the prenatal nucleus of its eye lens. Nuclear-test radiocarbon provides a useful bomb-pulse marker for some younger animals, while older sharks require comparisons with less certain deep-ocean chronologies. The 2016 study’s largest sampled female was estimated at 392 years, with a 95.4% probability range of roughly 272–512 years. That is compelling evidence of exceptional longevity, but it is not a precisely verified birthday—and no independent aging method has yet confirmed it.
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