Tag Archives: Isotopes

Raptors probably didn’t hunt in packs like they do in Jurassic Park

Velociraptors likely didn’t hunt in packs, at least judging from their teeth.

Image credits University of Wisconsin Oshkosh.

A new study from the University of Wisconsin Oshkosh looked at the chemical makeup of velociraptor teeth fossilized from specimens throughout their lives. The team reports that their findings suggest it’s unlikely that these lithe predators hunted in large coordinated packs as wolves would, which would mean that Jurassic Park got their behavior wrong.

Not big on teamplay

“Raptorial dinosaurs often are shown as hunting in packs similar to wolves,” said Joseph Frederickson, a vertebrate paleontologist and director of the Weis Earth Science Museum on the UWO Fox Cities campus.

“The evidence for this behavior, however, is not altogether convincing. Since we can’t watch these dinosaurs hunt in person, we must use indirect methods to determine their behavior in life.”

Jurassic Park features raptors (Deinonychus antirrhopus) hunting in packs to bring down large prey. And while they were undoubtedly fearsome beasts in real life, with their sickle-like talons and scary fangs, they probably didn’t hunt in packs.

The team explains that neither birds nor crocodilians, which are the closest living relatives of dinosaurs, hunt in groups, and they only rarely hunt prey larger than themselves. Since behavior can’t fossilize, they add, we have to rely on such circumstantial evidence to deduce their hunting patterns.

Another piece of evidence comes from a chemical isotope analysis the team performed on teeth recovered from raptor fossils of different ages. The idea was based on observations of Komodo dragons, a species in which infants may well be attacked and consumed by adults, so they take refuge in trees. They thus gain access to food resources that (the larger) adults don’t have, and this leaves a mark in the balance of carbon isotopes in their tissues — in this case, their infant teeth.

Animals that hunt in packs wouldn’t show any changes in their carbon isotope balances, as they would maintain the same diet throughout their lives since the pack helps feed everybody, regardless of age, from the same kills.

“We proposed in this study that there is a correlation between pack hunting and the diet of animals as they grow,” Frederickson said.

“If we can look at the diet of young raptors versus old raptors, we can come up with a hypothesis for whether they hunted in groups.”

Their analysis focused on fossilized Deinonychus teeth. This raptor species was native to North America during the Cretaceous Period about 115 to 108 million years ago. They analyzed levels of carbon and oxygen isotopes inside the teeth to get an idea of what they ate and drank. The data was compared to similar readings from a crocodilian and some herbivorous dinosaur fossils recovered in the same geologic formation.

The teeth point to a transition in the raptors’ diet as they aged, as the team found differences in the isotope values between the smallest and largest teeth.

“This is what we would expect for an animal where the parents do not provide food for their young,” Frederickson said. “We also see the same pattern in the raptors, where the smallest teeth and the large teeth do not have the same average carbon isotope values, indicating they were eating different foods.”

“This means the young were not being fed by the adults, which is why we believe Jurassic Park was wrong about raptor behavior.”

While the current research focused on raptors, the technique could be used to investigate the hunting and feeding patterns of other extinct species as well, the team concludes.

The paper “Ontogenetic dietary shifts in Deinonychus antirrhopus (Theropoda; Dromaeosauridae): Insights into the ecology and social behavior of raptorial dinosaurs through stable isotope analysis” has been published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.

A look at the hottest dating trend of 2020 — radiocarbon dating

Radioactive carbon dating determines the age of organic material by analyzing the ratio of different carbon isotopes in a sample. The technique revolutionized archeology when it was first developed in the 1950s, but is currently at risk from fossil fuel emissions.

Carbon is the main element in ash and charcoal.
Image via Pixabay.

Also known as radiocarbon or carbon-14 (scientific notation 14C) dating, the procedure relies on the rarest carbon isotope, carbon-14. Carbon-14 is created on Earth by interactions between nitrogen gas and radiation, usually in the higher levels of the atmosphere. With only 0.0000000001% of the carbon in today’s atmosphere being 14C, it is the rares naturally-occurring carbon isotope on our planet, the others being 12C and 13C.

Unlike the other isotopes, carbon-14 isn’t stable, and it decays over time. Its half-time, the time it takes for half of all 14C atoms in a sample to degrade, is 5,730 years. Putting together that tidbit of information, some very expensive machines, a big of educated guesswork, and ancient tree rings allows researchers to determine the age of a sample of organic material with reasonable accuracy.

Sounds a bit like magic, doesn’t it? Let’s take a look at how it works.

Who thought it up?

The theoretical foundations of radiocarbon dating were laid down by a research team led by American physical chemist Willard Libby in 1949. They were the first to calculate the radioactive decay rate of carbon-14 using carbon black powder. As a test, they took acacia wood samples from the tombs of two Egyptian kings, Zoser and Sneferu, and dated them. Their test showed the wood was cut in 2800BC +/- 250, where earlier independent dating estimated it hailed from 2625BC +/- 75 years — so their method checked out, mostly. There were still some flaws to the approach — the results were slightly fouled by nuclear weapon testing at the time — but these were soon worked out. One of the most important modifications to the initial method was to set the calibration date (we’ll get to this in a moment) to 1950.

For his work, Willard Libby would receive a Nobel Prize for Chemistry in 1960.

How does it work?

Most carbon atoms most have 6 protons, 6 neutrons, and 6 electrons.
Public domain image.

Carbon-14 is continuously created in the upper atmosphere: cosmic radiation ionizes nitrogen-14 gas atoms (which is native nitrogen and has 7 protons and 7 neutrons) into carbon-14 atoms (which have 6 protons and 8 neutrons). Interactions between radiation and the atmosphere at large supply the neutrons that collide with and kick protons out of the nitrogen atom. An atom’s chemical properties (i.e. the element) is a product of the number of protons in its nucleus, not its total mass — more on isotopes here — so this effectively transforms it into carbon-14.

These 14C atoms then get gobbled up by oxygen to become regular CO2, which is consumed by regular plants through photosynthesis, and these plants are then eaten by regular animals and so on. This is the process through which 14C becomes part of all organic matter. 14C has a half-life of 5,730 years, meaning that it takes 5,730 years for half of the 14C atoms in a sample to degrade back into nitrogen-14, and 5,730 more for half of what is left to degrade, and so on.

And here’s the kicker — when these organisms die, they stop taking in new carbon, including carbon-14. Since this latter isotope isn’t stable, it degrades over time. We know the rate it decays it at; so by comparing the current ratio of 12C to 14C atoms in a sample to the initial ratio, we can determine how long ago something died.

How do we do it?

An AMS device.
Image via Wikimedia.

There are three main ways to go about it, each with very sciency-sounding names: gas proportional counting, liquid scintillation counting, and accelerator mass spectrometry.

Gas proportional counting measures the amount of beta radiation — the kind of radiation given off during radioactive decay — emitted by a sample. In essence, it involves measuring the level of radiation it emits. Since 14C is the only radioactive isotope in organic material, this effectively tells you how much of it is in the sample. It gets its name from the fact that the sample needs to be transformed into carbon dioxide gas (basically, burned) before this measurement can be performed.

Liquid scintillation counting is another ol’ timer radiocarbon dating technique. It works on the same principle as gas proportional counting but uses different gear. The sample is turned into a liquid form and a scintillator is submerged in it. Scintillators are devices that emit flashes of light upon contact with a beta particle. Two additional devices (photomultipliers) are used to detect these flashes — when both pick up on it, a count is made.

Accelerator (or Accelerated) Mass Spectrometry (AMS) is the modern way of doing things, and over time has become more efficient, faster, and more accurate than the others. It is quite simple, actually — you physically count the number of 14C, 13C, and 12C in the sample using a mass spectrometer. AMS is preferred today for its speed and accuracy, but also because it works with much smaller samples than the other two, helping conserve precious artifacts. For this process, atoms in the sample are ionized (electrically charged) and accelerated using powerful magnets to gradually remove as many atoms not used in the counting as possible. Finally, the carbon-14 isotopes pass into a detector along with some other carbon atoms, and these are used to perform the measurement.

Calibration

“Quite quickly after radiocarbon dating was discovered, it became clear that Libby’s assumption of constant 14C levels in the atmosphere does not hold,” a paper published in 2008 explains. “The level is affected by very many complex factors that have proven impossible to model […] such as: solar cycles, solar storms, geomagnetic variations in the earth, and unpredictable up-welling of old carbon from substantial reservoirs such as oceans. The level has also been impacted by human activity; for example, it increased substantially due to atomic bomb testing in the 1950s and has dropped again more recently due to release of old carbon in fossil fuels.”

“As a consequence, radiocarbon dating is only viable if we can obtain an estimate of the varying level of 14C back through time and can thus plot the function that links radiocarbon ages to calendar ages.”

“Put loosely, we need a calibration curve.”

A marine calibration curve for the Northern Hemisphere extending up to 50,000 years ago. Notice that the curve shows an interval (blue surface) not a single value, and this interval becomes wider (more uncertain) the farther away you go.
Image credits Bronk Ramsey / P. J. Reimer et al., (2009), Radiocarbon.

While first developing their method of measuring 14C content, Libby’s team pointed to the possibility that the ratio of 12C to 14C in the atmosphere likely didn’t remain constant over time, but assumed it was as they had no way of correcting for it and wanted to finish their research. As radiocarbon dating saw more use and inconsistencies started to mount, researchers realized that his hunch was right, and set out to ‘calibrate’ the method.

Currently, the calibration date used for radiocarbon dating is the year 1950. In other words, samples are compared against the baseline value of 12C to 14C isotopes recorded in the 1950s. If a sample contains 25% of the carbon-14 you’d expect to see in an organism that died in 1950, it would be two times as old as the isotope’s half-life (so two times 5,730, giving it a rough age of 11,460 years). This isn’t the final age, however.

All the steps we’ve gone through so far don’t actually tell us how old a sample is, just much 14C it contains. As we’ve seen above, accurately dating such a sample hinges on us knowing how much 14C it contained to begin with. To know that, we need to know how much of it was in the atmosphere while the organism lived. This is the process of calibration: changing the assumed initial level of radioactive carbon. It’s perhaps the trickiest bit of the whole process.

“The convention is to assume that the [carbon isotope] ratio has remained constant over time and then to use calibration to compensate for the fact that, in reality, the ratio is changing,” Caitlin Buck, a professor in the Department of Mathematics and Statistics at the University of Sheffield told ZME Science. Professor Buck specializes in applying statistical methods to archeological and paleoenvironmental science and is the co-author of the 2008 paper above.

“At first the need to calibrate seems somewhat unfortunate but, in fact, it allows us to also compensate for several other underlying issues too, like the fact that (at any given time) the ratio in the atmosphere is not the same as that in the oceans.”

The most commonly used and reliable calibration methods are ancient trees. Since trees build a new set of rings every year, they act as 14C archives. From the data in the tree rings, a timeline of 14C levels can be constructed. Timelines from multiple trees would then be compared and overlapped, making this the most accurate record of the isotope we have. The simplest way to go about it would be to find a tree ring that contained the same ratio of radiocarbon as your sample. Other approaches include 14C curves compiled from other sources or to test artifacts that were reliably dated through other means, although this is more of a situational rather than a systemic solution.

Yearly variations in carbon ratios, however, are quite small, which is why radiocarbon dates often come with a “+/- years” variation interval.

Uncalibrated dates are denoted with the unit BP, meaning ‘radiocarbon years before present (1950)’. Calibrated dates use the unit calBP, ‘calibrated before present’. Calibrated dates are the final estimate for the sample’s age, but uncalibrated dates are routinely shown to allow for recalibration as our understanding of 14C levels through time increases. Researchers are putting a huge amount of effort into extending the calibration curve (a timeline of 14C:12C ratios throughout history) and to increase its accuracy. Currently, the curve extends to around 50,000 years ago, but with a relative degree of uncertainty over its oldest reaches.

Limitations and external factors

Image via Wikimedia.

For starters, if a reliable starting level for carbon-14 can’t be established, radiocarbon dating can’t be used to accurately determine a sample’s age. The technique can only be used to date samples up to around 55-60,000 years old (after which the carbon-14 content drops off to negligible levels). It’s also quite expensive — particularly AMS — due to the very sensitive and highly specialized equipment and personnel needed to run these procedures. Then, there are also external factors that can throw a wrench in the workings of radiocarbon dating.

Carbon-14 is created from the interaction between radiation and the atmosphere, and the advent of nuclear technology (with its plethora of weapon and civilian testing) released a great amount of radiation and radioactive material, driving up the atmospheric ratio significantly.

“The ‘bomb’ samples [i.e. those after 1950] have very high concentrations of 14C, and so if you are working on very old samples for archaeology it is a good idea to have separate extraction lines for the ‘low-level’ samples,” Thure Cerling, a Distinguished Professor of Geology and Geophysics and a Distinguished Professor of Biology at the University of Utah, told ZME Science in an email. “It is quite easy to contaminate ‘old’ samples with ‘modern’ 14C, so a lot of effort has gone into dealing with that issue.”

On the other hand, all that nuclear weapons testing makes it very very easy to date a sample of organic matter that grew during this time, being one of the reasons why 1950 was selected as a calibration date. “Organic material formed during or after this period may be radiocarbon-dated using the abrupt rise and steady fall of the atmospheric 14C concentration known as the bomb-curve,” explains a paper co-authored by Professor Thure in 2013.

He cautions that you must be “very careful” to prevent this kind of contamination, although noting that the issue “is well known” and that “most modern labs have taken sufficient precautions that it is not the problem that it was 30 to 40 years ago.”

Another element affecting this ratio is the use of fossil fuels. Fossil fuels are originated from organic matter, but because they’re formed over millions of years, all the carbon-14 they might have contained has degraded. So when they are burned and their carbon released as CO2 in the atmosphere, it’s pure carbon-12. This further affects the carbon isotope ratio, and does it very fast, impacting the reliability of our dating efforts. Together, these two factors stand testament to the wide reach humanity has achieved over the Earth.

Contamination with external material such as soil can alter the apparent age of a sample by mixing in extra carbon; therefore, all samples are thoroughly cleaned with chemical agents to remove any contaminants. Reservoir effects — this refers to the fact that ocean water contains a different ratio of carbon isotopes than the atmosphere — need to be taken into account when dealing with samples that have been submerged or originate from aquatic environments.

In closing

Radiocarbon dating revolutionized archeology and anthropology by giving researchers a quick and reliable tool to date organic materials. It was a boon to these fields, one whose merits are very hard to overstate. Both Prof Buck and Prof Cerling pointed to the method’s ability to yield absolute age measurements for items of interest — with Prof Cerling saying that it “has revolutionized archaeology” — which allowed us to make heads and tails of historical timelines. Previous approaches such as seriation could only be used to date structures, cultures, and artifacts in relation to one another through the ample application of good, old-fashioned time and labor.

“Likewise it is very useful in determining the age of ice in ice cores that record the history of CO2 and methane in the atmosphere,” Prof Cerling told me.

But radioactive carbon isn’t useful just for dating stuff. Used as a marker molecule, it can allow researchers to, for example, trace specific drugs as they spread through the body, how masses of water move through the oceans, how carbon circulates in nature, and even in forensics to determine when an unknown person died.

Not bad for an unstable isotope of the Earth’s most abundant element.

Physical, encryption-like method could help the world finally get rid of nukes

MIT researchers have devised a method that could allow states to prove they’re disposing of nuclear weapons without giving away any of their technical details — which are considered state secrets.

Mark 5.

Open nose cavity US Mark 5 nuclear bomb showing the ‘pit’.
Image credits Scott Carson / US Atomic Energy Commission.

Nuclear disarmament negotiations (particularly those between the U.S. and Russia) always hit a patch of rough ground when verification processes come up. The main point of these talks is to promote nuclear non-proliferation — the understanding that the fewer nukes there are in the world at any one time, and the fewer actors there are with access to them, the easier it will be for humanity not to blast itself back to an irradiated stone age. However, every reliable verification process that the two parties could agree on as trustworthy (i.e. visually identifying the warheads) would give away technical data pertaining to the weapons.

This would never fly. For starters, governments don’t like other people to know how their nukes work — especially the people they’re generally aiming said nukes at. Secondly, such measures would risk disseminating technical details to third-parties, thereby defeating the whole purpose of disarmament efforts. Visual confirmation, then, became a no-go.

To spot a warhead

Now, an MIT research team reports developing a novel method of confirmation that could help promote nuclear disarmament without disseminating any state secrets. The method, similar to a physics-based version of cryptographic encryption systems, can be applied in two different versions — just in case one is found to have drawbacks by any government. The findings were published in two different papers.

Lacking a reliable tool to identify nuclear weapons, and thus bereft of a way to enforce their destruction, past agreements have focused on decommissioning of delivery systems. It makes sense, as it’s far harder to ‘fake’ a plane or a ballistic missile, whereas nuclear bombs are basically spheres of plutonium. Such measures have worked reasonably well up to now, but lead author Areg Danagoulian believes that it only skirted the real issue: to avoid such weapons falling into the hands of terrorist or rogue states, we need to dispose of the actual warheads — which means we need a reliable way to identify them or spot fakes, one to which governments will agree.

“How do you verify what’s in a black box without looking inside? People have tried many different concepts,” Danagoulian says. “But these efforts tend to suffer from the same problem: If they reveal enough information to be effective, they reveal too much to be politically acceptable.”

Their solution draws inspiration from digital data encryption methods, which alter data using a set of large numbers, which form the key. Without this key, the encrypted data is a hodge-podge of characters. However, while it may be illegible, it is still possible to tell if it is identical to another set of encrypted data — if they use the same key, the datasets would be the same hodge-podge. Danagoulian and his team applied the same principle for their warhead verification system — “not through computation but through physics,” he explains. “You can hack electronics, but you can’t hack physics.”

The method analyzes both of a warhead’s essential parts: the sphere of radioactive elements that supply its nuclear ‘gunpowder’, and the dimension of the hollow sphere called a pit that serves as a ‘detonator’ — details pertaining to both elements are considered state secrets. Because of this, they couldn’t simply probe the weapons’ internal characteristics, and they couldn’t tell a fake apart just by measuring emitted radiation.

Negative filter

So what the team did was to introduce a physical key, created from a mix of the same isotopes used in the weapon, but in a ratio unknown to the inspection crew. Similarly to a filter applied to a photo, the key will scramble information about the weapon itself. In keeping with that analogy, the physical key is like a complementary color filter (a picture’s negative) that will cancel out all of the weapon’s emissions when lined up properly. If the investigated object has a different emission pattern (i.e. it’s a fake), it will bleed through the filter, alerting the investigation crew.

Nuclear verification.

(Top) diagram showing the configuration that could be used to verify that a nuclear warhead is real. (Bottom left) measurement without the reciprocal. (Bottom right) measurement with the reciprocal.
Image credits Areg Danagoulian.

This filter — called a cryptographic reciprocal or a cryptographic foil — will be produced by the same country that made the warheads, thereby keeping their secrets safe. The weapon can be hidden in a black box to prevent visual inspection, lined up with the foil, then get blasted with a beam of neutrons. A detector will then analyze the output and render it as a color image — if the warhead is genuine, the image will be blank. The second variant of this process substitutes a photon beam for the neutron one.

These tests are based on the requirements of a Zero Knowledge Proof — where the honest prover can demonstrate compliance, without revealing anything more. It also benefits from a built-in disincentive to lie. Because the template is the perfect complement of the weapon itself, when superimposed over a dummy it will actually reveal information about the warhead’s composition and configuration — the very things states don’t want others to know about.

It’s a neat concept; the only issue I have with it right now is that it only works if all parties involved are genuine, and do actually create the right reciprocals for their warheads. Still, if the system does someday get adopted and helps bring about significant reductions in the number of nuclear weapons in the world, Danagoulian says, “everyone will be better off.”

“There will be less of this waiting around, waiting to be stolen, accidentally dropped or smuggled somewhere. We hope this will make a dent in the problem.”

The papers “Experimental demonstration of an isotope-sensitive warhead verification technique using nuclear resonance fluorescence” has been published in the journal Proceedings of the National Academy of Sciences; “Nuclear disarmament verification via resonant phenomena” has been published in the journal Nature Communications.