I’m familiar with carbon 14 being generated by cosmic rays, then entering the food chain through photosynthetic plants and then eventually consumed by animals. I’m comfortable with the idea that carbon dating animal bones/flesh is tied to when the plant derived carbon winds up in the animal and that animal dating is pretty much contemporary with the plant that was previously consumed. The carbon may have been in the plant for a few months or a couple of years before it winds up in our own bodies… and likely that carbon was not in the plant for multiple decades before it winds up in us.
I’m not so sure about the carbon that has entered the eye lens of an embryonic or young greenland shark. The assumption is that the carbon 14 that goes into the shark lens is also generally about the same age as the autotrophs that fixed the carbon and were subsequently eaten by the heterotrophs and eventually consumed by the shark…or the sharks mother.
It seems this idea of contemporary carbon 14 fixation is an assumption that may not be correct for these sharks. I could see that the carbon 14 that was created takes some years to enter the water column and be absorbed by algae, and then quite possibly even more years to exist in various fishes before getting consumed by a greenland shark. Plus, I would think that a lot of the carbon gets recycled in the food chain from decaying flesh, back to organism that eventually wind up in the shark lens. So that carbon may have been cycling through the ocean system for quite some time. As such, I’m not really convinced that the carbon in a shark lens actually contains relatively ‘newly’ formed carbon 14. I think there is an argument that would say this carbon 14 in the lens was actually ultimately formed many years (decades? hundreds?) prior; giving an erroneous analysis of the true age of a greenland shark.
According to this very, very brief summary they are targeting their dating to a protein that forms pre-birth, and then is supposedly stable. I’d read that to mean that it sits there like an unwanted donut and is not replaced at a cellular level. I guess if that was not the case then it would read close to 0 years old regardless of evident age.
Some possible cross-checks could be from bone growth rings. Apparently sharks do not have otoliths, which is how many fish specimens can be aged, but may have other structure that picks up annual cycles.
Yes, I understand that they are targeting a protein that has carbon laid down pre-birth (or even shortly as the young pup grows.) My question is regarding: what is the origination of that carbon 14? and how do we know it was formed relatively contemporaneously with the birth of the shark…and not carbon that has been ‘hanging around’ in the ocean for decades or centuries?
One cross-check is that only really young sharks have the ‘bomb signature’ in their radiocarbon. So that acts as a control/calibration for overall analysis.
Thanks.
I searched for some of the research papers, and it seems that the bomb signature is the key measurement. Its not ‘traditional’ carbon isotope ratios as I understand them. Rather its the characteristic presence of the bomb signature in what are perceived as ‘teenage’ (~50 year old) sharks…those that are 2.5 meters or so. Other research has shown that these sharks grow less than 1cm a year. The implication is that these 2.5 meter sharks are ~50 years old, and in order for a shark to grow 6 meters in size implies they would have to have been growing for 350 years or more.
I think this satisfies my understanding and recognize that there are some assumptions which result in a fairly large standard deviation in the age estimates.