Hacker News

24 Comments:
pvaldes said 2 months ago:

In my experience, bony fishes are not easy to date by counting rings. I tried it and discarded the whole work. If you find 20 rings, you can assume that the fish would have 10 years (one opaque ring in summer and other hyaline ring for winter), but unfortunately there are also bifurcated rings, disease's rings, fused and duplicated rings so your animal could have several false duplicated rings, and have only 7 years. In 200 thin rings your error can be awful.

To know the sex of the animals is also important, because females will produce extra hyaline spawn rings starting somewhere in their adult phase. And males... well, nobody nows. They obviously do not get pregnant but do the male whale sharks fight and stop eating?. Not to mention than some fishes can change its sex perfectly.

This with bony fishes, that have true bones. Big sharks are cartilaginous fishes. Cartilaginous tissue dyes badly and rings in its vertebra are less clearly marked. This animals migrate (vertically and horizontally). This means that would probably starve for long periods and then feast and that their vertebras would be subject to a wide range of pressure that could erase rings.

> So any animal that was alive then incorporated that spike in Carbon-14 into their hard parts

The key of the phrase is hard parts. They are looking at cartilage, that is not hard and is a very slow growing and inert structure (what if most of all carbone went to the muscle instead?). The only hard part in whale sharks is the tooth (1-5 milimeters long if I remember correctly). Those teeth are lost and replaced continuously so can't be used to age the animal. Even more, they are releasing carbon-14 at a unknown rate. I would like to see how they address this fact as source of error in their models.

I remain still sceptical when I read this kind of results. Tagging or photoidentification could help, but our best chance is with captive animals.

x3n0ph3n3 said 2 months ago:

> I tried it and discarded the whole work.

Why wouldn't you publish on how it can't be done reliably?

pvaldes said 2 months ago:

It just didn't pass the cut. I had plenty of other interesting questions to chew, and moved on. There is not reason anymore to revisit it. Most of those bones would be unreadable today in any case.

dang said 2 months ago:

What a great post. That one's going in the next highlights list, if we ever revive those.

https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...

walkingolof said 2 months ago:

A method like this was used to determine the age of the Greenland shark, a large shark living in cold waters.

"In 2016, a study based on 28 specimens that ranged from 81 to 502 cm (2.7–16.5 ft) in length determined by radiocarbon dating of crystals within the lens of their eyes, that the oldest of the animals that they sampled, which also was the largest, had lived for 392 ± 120 years and was consequently born between 1504 and 1744"

https://en.wikipedia.org/wiki/Greenland_shark

pvaldes said 2 months ago:

> had lived for 392 ± 120 years

Is the same problem, I personally (is just my opinion) wouldn't discard that where 392 solid meals instead, one seal or reindeer at a time boosting grow periods between nape and nape, minus an unknown number of pregnancy events.

Scientists are forced to publish something, anything, in short periods of time, so here we are. And is getting worse.

bpodgursky said 2 months ago:

Radiocarbon dating wouldn't be affected by meal frequency, unless I'm missing something. It's just identifying the oldest material in the specimen.

pvaldes said 2 months ago:

We have two main different ways to attack the problem of age, and both have issues

> But as scientists know the rate at which this isotope decays, it is a very useful marker in determining age... The older the creature, the less Carbon-14 you'd expect to find.

They are registering decay in the level of carbon-14.

The clock is adjusted for bone (storing this isotope as a more or less permanent crystalline mix of carbone and calcium). This is cartilage.

And teeth in sharks last only for some period ranging between, lets say, two weeks and two years (100 days for a white shark or so). Somewhere inside this period, those pieces storing carbon-14 will fall and will need to be replaced in a few days. If the reserves are mobilised from vertebra to tooth, then you would expect to find much less carbon-14 than usual.

Therefore you could conclude than the fish is much older than it really is.

Counting the number and type of rings on vertebra is a different problem, and is affected by fasting and starving periods.

said 2 months ago:
[deleted]
kgwgk said 2 months ago:

How would those events change the crystals within the lens of their eyes?

pvaldes said 2 months ago:

Unlike us, fishes have continuous growing. And also unlike us, they do not use sugars. Its main source of energy is fat, that they store either in the whole body or in the liver. Sharks belong to the second group (something than was basic for the development of precision machines and robotics in fact).

Being cold blooded species, fishes rely on the water temperature to warm itselves. When the temperature decreases under the viable range for its enzimatic gut activity, they stop eating, get sluggish and enter in "saving energy mode" until the circumstances got favourable again (instead to spend valuable resources chasing preys that they can't digest anymore).

In a long migration through open sea they will cross extensive low-density preys areas and the result is similar.

If the fat reserves eventually get depleted the fishes need to resort to its second and last source of energy: Proteins.

They start burning muscle, recycling its proteins as fat and burning this fat. Fishes do this routinely when needed and can "de-grow" to some extent, shrink and recover quickly later. Sharks are particularly well adapted to alternate periods of feast and famine.

In case of emergency, we can burn proteins in a similar way, but, unlike us, the weigh of aquatic animals is supported by water in part, so its skeletons are also reduced. Our skeletons are always saved until the last minute (We need it more than fishes need theirs). And this is the part used in carbon-14 tests.

As proteins (like those in eye lenses) and fats are made of carbone, almost anything non indispensable in a fish body can be recycled and burn instead.

Eyes are not essential structures for deep-water sharks (can rely in olfactory, electric and water pressure receptors instead), so if in a hurry, they can assign less resources for their maintenance. The result is that the eye lense will grow slower and with a lighter (cheaper) structure, therefore you have a more transparent area. A feasting period instead means some extra calcium (or other matherials) assigned to the eye maintenance. This is what makes the structure "readable" as a series of bands alternatively opaque and hyaline.

kgwgk said 2 months ago:

They are looking at those proteins in the nucleus of the lens of the eye for a reason. Didn’t you wonder why?

“In vertebrates, the eye lens nucleus is composed of metabolically inert crystalline proteins, which in the center (i.e., the embryonic nucleus) is formed during prenatal development (6, 7). This tissue retains proteins synthetized approximately at age 0 – a unique feature of the eye lens that has been exploited for other difficult-to-age vertebrates (6, 8, 9).”

https://ora.ox.ac.uk/objects/uuid:6c040460-9519-4720-9669-99...

“Because the epithelial basement membrane (lens capsule) completely encloses the lens, desquamation of aging cells is impossible, and due to the complete absence of blood vessels or transport of metabolites in this area, there is no subsequent remodelling of these fibers, nor removal of degraded lens fibers. [...] The lens fibre cells in the nucleus of an adult lens are thought to be produced during early embryonic life [2]. The lens plate is formed in the 4 mm embryonal stage. The lens fibre cells degrade all membrane-bound organelles and the older lens cells become compressed into the nucleus of the lens by the continuous formation of new fibres at the surface.”

https://journals.plos.org/plosone/article?id=10.1371/journal...

pvaldes said 2 months ago:

Thanks for the links. It clears many things, but the main problem stills remain.

Let me put you this example problem. "We have a box full of marbles and we can take two marbles out of the box each day. How many time it would take us to empty the box of marbles?

As you had noticed yet, this is an unsolvable problem

Now lets assume than we examine a Greenland shark's eye lense and register a value of "X" remaining radioactive carbon-14 atoms and then we take a look to a human eye lense of known age and found "Y" remaining radioactive C14 atoms.

To simplify the problem we will assume that all atoms in a eye lense are trapped there forever, no new carbon atoms were physically added or removed, and the size, weight, and fiber density in the lense are the same for both human and shark.

Having in mind that decay ratio is independent on taxonomy and there is not any reason to think that radioactivity would decay faster in a particular vertebrate... if X = Y; could we conclude than the shark and the human had the same age?

The answer is: Not, we can't infer the shark age. And this is the same problem than with the box of marbles.

kgwgk said 2 months ago:

I don’t understand what you’re talking about.

Do you mean that radiocarbon dating of organic material in general is impossible?

Do you mean that radiocarbon dating of the embryonic nucleus of the eye lens of a vertebrate in particular is impossible?

pvaldes said 2 months ago:

Both are possible if, and only if, some conditions are fullfilled first. I don't see nothing in the article suggesting that, and I spot at least one serious flaw in the design.

But I don't know everything, and I could be wrong, obviously.

kgwgk said 2 months ago:

There are several papers and theses (including this one about the Greenland shark http://www2.bio.ku.dk/bibliotek/phd/Julius%20Nielsen.pdf) looking at the isotopic profile of the different layers of fish eye lenses, down to the embryonic nucleus. Maybe all those researchers are onto something. Or maybe they are all wrong. I have no dog on this fight anyway.

hprotagonist said 2 months ago:

You can play a similar radiocarbon dating trick with the lenses of greenland sharks. They live to about 390 +/- 120 years old, and are estimated to reach sexual maturity at 150 years old.

A specimen analysed in 2016 was born somewhere between 1500 and 1740.

https://science.sciencemag.org/content/353/6300/702.full

Zenst said 2 months ago:

"Over time, every living thing on the planet has absorbed this extra Carbon-14 which still persists."

Is that as consistent in absorption? More so animals that feed upon different levels and maybe more so - do plankton absorb more or less and any animal feeding upon them would see a higher rate perhaps. I'm still looking into these aspects - fun google time. #1

Another train of thought I have from reading this is: We may well read in the future about plastic pollution being used to measure metrics in life forms. [EDIT ADD]

#1

https://en.wikipedia.org/wiki/Carbon-14

It is naturally formed by cosmic rays, it has also been measured as highers in area's that atomic testing happened (so near Australia) and with that, Southern hemisphere. Given that, one would expect, any life form that was located near area's near the poles or southern oceans would be more exposed to the natural and atomic unnatural sources and whilst the unnatural sources would dissipate - anything exposed during the early times would also have higher levels than such a lifeform in those same area's today due to decay and dispersion.

gus_massa said 2 months ago:

I think you can assume they didn't change the diet too much, so before 1945, measuring the carbon in the bones(?) you should get a nice smooth exponential curve, and then a jump in 1945 [Is there a small delay?]. More details in https://en.wikipedia.org/wiki/Bomb_pulse

Zenst said 2 months ago:

Whilst their food would not of changed in source, the content would of had spikes above global average it periods of time due to the atomic spike, also how that dispersed and how long until equilibrium would all be factors that come into play. Let alone natural hotspots from solar radiation increase near the poles.

But then the error +/- rate would seem to accommodate those kind of margins, but always nice if there is a way of narrowing those margins, so may be a field of research that has some headroom and also help learn many other tangents and maybe another data point for historical solar radiation.

said 2 months ago:
[deleted]
pjc50 said 2 months ago:

It is rather remarkable that nuclear weapons have left a legacy written at the atomic level in every living creature.

jmiskovic said 2 months ago:

And not just in living creatures. Ships sunk before atomic tests are valuable source of "low-background steel".

https://en.wikipedia.org/wiki/Low-background_steel

skoskie said 2 months ago:

100-150 years old.