Just How Long Does DNA Last?

The moa can be considered New Zealand’s equivalent of the Mammoth. Both were large animals hunted to extinction by humans in relatively recent history. Sightings of both are occasionally claimed, deep in the forests. And both invoke optimistic hopes that they could be someday cloned, and returned to their ancient grasslands. The moa is also the animal in the picture to the right, and the icon for this blog is a moa footprint – as you might have gathered I’m rather fond of them. They last properly came up on this blog eleven months ago, in The Extinction of the Megafauna, but in today’s post – Bone DNA Decays Too Fast for Evolution – Brian Thomas brings them up in quite a different context. For those readers unfamiliar with the soft-tissue family of young Earth creationist claims, think radiometric dating – and be prepared to have your expectations completely reversed.

DNA is a biochemical that contains genetic information. And like all other cellular ingredients, it decays if cellular systems don’t maintain it. Now, scientists are more confident about how fast it falls apart after a cell dies.

A team of researchers recently completed a thorough investigation of 158 ancient leg bones that belonged to giant extinct birds called moa, which once lived on New Zealand’s South Island. Using radiocarbon ages and measures of DNA integrity, the researchers generated a DNA decay rate with unprecedented rigor. But their results do not fit with claims from secular scientists who have found plenty of examples of intact DNA from supposedly million-year-old samples.

They used radiocarbon dating and produced a result with “unprecedented rigor”? How… odd for Mr Thomas to say such a thing.

To nitpick, the moa lived in the North Island as well as the South – these bones were from the south, however, which may be what misled Thomas. The paper is The half-life of DNA in bone: measuring decay kinetics in 158 dated fossils, and while the ICR helpfully provides a pubmed link (for once) the full paper can be found online at the Proceedings of the Royal Society B website.

With access to the full paper we can see that the introduction begins like so:

Although early-1990s claims of DNA recovered from million year-old fossils [1–4] are now widely regarded as modern contaminants [5–13], the kinetics of long-term post-mortem DNA decay is still poorly understood.

The authors clearly do not have much stock in the million year old DNA claims. We’ll get back to that later.

The moa bone researchers, publishing in the Proceedings of the Royal Society B, discovered that after only 10,000 years, DNA strands in bone would be so far dilapidated that DNA sequencers could no longer process it.

The much more important figure that Brian never mentions in this article is the calculation that, at −5°C (which they claimed was optimal temperature), it would take 6,830,000 years for DNA to decay completely. Not only that, but I can’t say where the study actually says what Brian claims. A table is provided that gives, among other figures, the average length of a DNA fragment after 10,000 years, and this is likely the source of the number. The appeal for a young Earth creationist of a number only slightly greater than their claimed age for the Earth cannot be overstated.

They found that their DNA decay data best fit a logarithmic decay model, which follows the molecule’s initial disintegration into large fragments as happening faster than its later disintegration into smaller fragments. At room temperature, they measured the half-life of DNA to 521 years. After this time, only half of the amount of DNA present when the animal cells died should remain. And after another 521 years, only half of what remained after the first half-millennium would remain, and so on until none remains.

(He obviously meant an “exponential decay model” there.) In a footnote here Brian explains his earlier radiocarbon reference:

Specifically, this is their determined half-life for a 242 base-pair segment of mitochondrial DNA called the control region. The researchers calibrated this result using time in years from carbon dating the fossils bones. Although carbon dating is unreliable in older samples, it often provides reasonable age information for objects within the relatively recent time range of these moa bones. See: Aardsma, G. A. 1989. Myths Regarding Radiocarbon Dating. Acts & Facts. 18 (3).

That article is actually quite good, at least in some of it’s points. For one, it actually refutes the “coal contains carbon-14” claim, which we see so often (though usually referring to diamonds instead). Conversely Aardsma did not make a very strong case for what Thomas claims, casting disproportional doubt on older dates based solely on the differences between calendar and radiocarbon years – said differences are not nearly large enough to justify the chronology-mashing that YECs like to get up to, and are accounted for in calibration curves.

Inconsistent results have frustrated prior attempts to measure DNA’s decay rate, probably caused by differences in setting, nearby chemistry, amounts of water, and other factors that accelerate the inevitable chemical DNA decay. This project minimized variables by focusing on the moa bones, which experienced consistent temperature and burial conditions, and by analyzing so many of them.

This should be a huge red flag. The decay rate of DNA varies significantly in accordance to the conditions, and the claim by Thomas that all factors cause an acceleration seems to be his own invention.

The aim of the study was threefold:

The three main objectives of this study were: (i) to test whether long-term DNA decay follows first-order kinetics, thereby confirming the foundation for a predictive model; (ii) to estimate the long-term decay rate in bone at a given burial temperature and compare this rate with the predicted depurination rate from DNA in solution [21,22]; and (iii) to estimate the relative importance of storage time on DNA preservation in bone.

So: does DNA actually follow an exponential decay and have a half life? If so, how fast is it? And what affect does the time from excavation to measurement have on the survival of DNA? They really were starting from the beginning.

In there is mention of a comparison to predicted values. In the abstract they say:

With an effective burial temperature of 13.1°C, the rate is almost 400 times slower than predicted from published kinetic data of in vitro DNA depurination at pH 5.

I bring this up because you occasionally see creationists bringing up how predicted rates for soft tissue degradation would exclude the possibility of old finds. As the above shows, those numbers really aren’t trustworthy – but you don’t see Brian bringing it up.

The results of the study are debatable in their applicability beyond the specific conditions that they tested, at least for part ii. The 521-year figure, as B.T. said earlier, is for mitochondrial DNA. Nuclear DNA was estimated to degrade several times faster than mtDNA, which should show just how variable changes in conditions can make the results. But let’s assume, for a moment, that the figures are widely relevant and rule out the dinosaur DNA.

So, one set of secular scientists presented a DNA decay rate that precludes millions of years, and another set of secular scientists presented DNA from fossils deemed to be millions of years old. Both cannot be right.

One commenter on the Nature News report of this new DNA half-life posted, “This is nonsense. There’s been dozens and dozens of reports of DNA isolated from sources orders of magnitude older than 521 years,” along with cited reports of ancient DNA.

That report is here, with the comment in question coming from ‘D Schlesinger.’ There are many other comments – ‘E. Andersson’ said:

Those articels [sic] are from the early 1990’s and have since been rejected:
http://mbe.oxfordjournals.org/content/15/7/926.full.pdf etc.

If there would have been possible to isolate DNA that were 120 million years old back then, people would have made many such studies today.

Schlesinger responded:

@Andersson, there are dozens and dozens of articles that have shown DNA can be isolated from organisms many millions of years old. It’s preposterous to say that they have all been rejected. Please show me the retraction notices for each publication. And your citation is specific to DNA isolated from amber.

Here we return to the question of whether or not those ancient DNA finds were genuine. In my research on this topic in the past I have got the impression that there is a serious cloud hanging over at least some of the claims, which do indeed seem to be predominately from the early 1990’s. I don’t have nearly enough knowledge of the field to rule out all of the studies, but Schlesinger makes much too great of a demand for evidence to show that they are false. We are unable to provide the true sequence of events that surround each and every UFO claim, for example, but I can still be quite confident that they aren’t true without that. Retraction notices for each and every paper is overkill. Even if this paper is correct, then, we need not have a paradox – the threat of contamination is very real.

Returning simultaneously to the real world – where the conclusions of this paper may not actually be universal – along with Brian Thomas’ fantasy world, we conclude the ICR article:

Should the supposedly million-year-old DNA from fossils justify calling this study’s analysis of 158 bones “nonsense,” or should the analysis of 158 bones call into question the age labels of reportedly ancient DNA samples? Secular scientists have been processing the same vexing questions for decades regarding protein decay rates and proteins found in fossils, including dinosaur bones.

But abandoning the millions-of-years dogma in favor of a young world solves the whole problem. Ancient DNA is in the fossils and DNA half-life is short, which makes perfect sense if the fossils are only thousands, not millions, of years old.

The great irony in this article comes when you compare it to radiometric dating. Radiometric dating is reliable, and it does match the predictions. It also shows an obviously old Earth, so creationists like Brian like to attack it in any way they can. But this new DNA halflife is not reliable (and it’s certainly not an upper bound), and yet it’s apparently good evidence that the Earth is young. Quite a contradiction.

In conclusion, I would be quite hesitant to say that this study completely rules out the possibility of preserved dinosaur DNA – there seem to be just too many aspects to consider. But I wouldn’t want to claim that the reported cases of ancient DNA are themselves solid either. Either way, this paper does not prove a young Earth.