Thursday, 17 November 2022

How Science Works - Self-Correcting by Critical Revision

Footprints Claimed as Evidence of Ice Age Humans in North America Need Better Dating, New Research Shows - DRI
Human footprints in Tularosa Valley, New Mexico
The ancient human footprints found at White Sands National Park in New Mexico, the United States.

Here is an example of how science is self-correcting in that methods are critically scrutinised, especially if the reported results look far out of place with other known data. It's the sort of thing that Creationist frauds often find irresistible as something to misrepresent, as either science changing its mind, showing science to be unreliable, or scientists looking for an excuse to change the conclusion because it didn't conform to scientific 'dogma'. It's neither of those things, of course. It just one team of researchers offering a suggestion as to why another team might have been wrong.

It concerns a 2021 paper published in Science by a team from Institute for Studies in Landscapes and Human Evolution, Bournemouth University, Poole, Dorset, UK, led by Matthew R. Bennett which reported the discovery of human footprints preserved in sand deposits in White Sands National Park, New Mexico, USA, in the what had been the sediment in Lake Otero at the bottom of Tularosa Valley, which had been dated to between ~23 and 21 thousand years ago. The problem was, this placed them at the height of the last glacial maximum, long before other evidence suggested modern humans migrated into the Americas from Siberia.

That conclusion has now been challenged by a second team of scientists from The Desert Research Institute (DRI), Kansas State University, the University of Nevada, Reno, and Oregon State University, led by Professor Charles Oviatt, with some fairly hefty evidence. They have published their findings in the journal Quaternary Research.

Dating fossils such as these is done by radiocarbon dating plant remains embedded in the same rock formation, and this highlights a problem, not with radiocarbon dating per se, but with the choice of sample.

Briefly, radiocarbon dating relies on the fact that the nitrogen in the atmosphere is bombarded with solar radiation, turning a fraction of it into the radioactive isotope of carbon, 14C, which decays back to nitrogen at a known rate. The 14C reacts with oxygen to create radioactive carbon dioxide (CO2) and that CO2 gets taken up by living organisms such as plants. While the organism is alive the CO2 is in equilibrium with environmental CO2, but when the plant or animal dies, the amount of radioactive CO2 is fixed and the 14C begins to decay back to nitrogen at a known, constant rate, with a half-life of 5,730 years, which means in any sample, half of it will have decayed in 5,730 years. Half of the remainder with have decayed in a further 5,730 years, and so on.

Because the amount of solar radiation fluctuates over time the creation of 14C is not entirely constant and obtained dates are corrected for these known fluctuations as recorded in tree rings. Another correction is needed to allow for the fact that since the Industrial Revolution, mankind has been burning fossil fuels and increasing atmospheric CO2 with a source that lost all its 14C long ago.

So, by measuring the amount of 14C compared to the amount of 'normal' (non-radioactive) carbon, (12C) scientists can work out how much there was to begin with and so how long ago the organism died.
Now, that depends on the remains of the organism being used for radiocarbon dating getting its CO2 from the atmosphere, and this is where the Professor Oviatt team believe the Bournemouth team make a mistake. The clue is in a sentence from the 2021 paper, "We established chronological control for the footprint-bearing sediments by using radiocarbon dating of in situ layers of macroscopic seeds of the aquatic plant Ruppia cirrhosa". But, Ruppia cirrhosa is an aquatic species which gets most of its CO2 from that disolved in the water it lives in, and the CO2 dissolved in water can come from several different sources, including the bedrocks and rocks thorough which feeder streams flow. Lake Otero received most of its carbon in the form of calcium carbonate from the limestone of the surrounding hills.

So the basic assumption behind radiocarbon dating (that the CO2 in the living organism will be in equilibrium with atmospheric CO2 with its constant supply of 14C) is not valid in this particular case.

Professor Oviatt's team were able to demonstrate this flaw in the dating method the Bournemouth team used by radiocarbon dating dried samples of Ruppia cirrhosa, collected for the University of New Mexico’s herbarium. Living samples had been collected from a nearby spring-fed pond, dried and archived in 1947, so an exact date when the plants died was known without any doubt. These were radiocarbon dated to 7,400 years old! Hence the aquatic source of 14C in the seeds of Ruppia cirrhosa, recovered from the rock, had distorted the result.

If the Bournemouth team had been aware of this, they would have corrected their date to take account of it and would have arrived at a date of between 15 and 13 thousand years, much more in line with what is known of human migration into North America and the extent of the glaciers in Canada

and The DRI news release explains the background to the research and what the team found:
The wide expanse of an ancient lakebed in New Mexico holds the preserved footprints of life that roamed millennia ago. Giant sloths and mammoths left their mark, and alongside them, signs of our human ancestors. Research published in September 2021 claimed that these footprints are “definitive evidence of human occupation of North America” during the last ice age, dating back to between 23 and 21 thousand years ago. Now, a new study disputes the evidence of such an early age.

Scientists from DRI, Kansas State University, the University of Nevada, Reno, and Oregon State University caution in Quaternary Research that the dating evidence is insufficient for claims that would so radically alter our understanding of when, and how, humans first arrived in North America. Using the same dating method and materials, the new study shows that the footprints could have been left thousands of years later than originally claimed.

I read the original Science article on the human footprints at White Sands and was initially struck not only by how tremendous the footprints were on their own, but how important accurate dating would be. I saw potential problems with the scientific tests of the dates reported in the Science paper.

Professor Charles Oviatt, lead author
Emeritus professor of geology
Kansas State University, USA.

It really does throw a lot of what we think we know into question. That’s why it’s important to really nail down this age, and why we’re suggesting that we need better evidence.

23 to 21 thousand years ago is in a timeframe where you need to really pay attention to how people got into North America. At that time, there was a huge, mile-high mountain range of ice covering Canada to the north, and the pathway down the Pacific Coast wasn’t very accommodating either – so it may have been that people had to come here much earlier than that.

While the researchers recognize the problem, they underestimate the basic biology of the plant, For the most part, it’s using the carbon it finds in the lake waters. And in most cases, that means it’s taking in carbon from sources other than the contemporary atmosphere – sources which are usually pretty old.

These trackways really are a great resource for understanding the past, there’s no doubt about that. I’d love to see them myself. I’m just cautious about the ages that the researchers put to them.

Dr David Rhode, PhD, c-author
Desert Research Institute (DRI)
Archaeologists and historians use a number of methods to determine the timing of historic events. Based on these methods, scientists tend to agree that the earliest known dates of humanity’s colonization of North America lie between 14 and 16 thousand years ago, after the last ice age. If the original claims are correct, current chronological models in fields as varied as paleogenetics and regional geochronology would need to be reevaluated.

By studying ancient DNA from human fossils and using rates of genetic change (a sort of molecular clock using DNA), paleogeneticists surmise that the American Southwest was first occupied no earlier than 20 thousand years ago. If the footprints are older, it throws into question the use and integrity of these genetic models. It’s possible that the ages from one study at a single site in a New Mexico lake basin are valid, and that age estimates from a variety of other fields are invalid, the authors write, but more robust evidence is needed to confirm the claims.

At the center of the debate are the tiny seeds of an aquatic plant used to age the footprints. The timeframe for the seeds was identified using radiocarbon dating methods, in which researchers examine a type of carbon known as Carbon-14. Carbon-14 originates in the atmosphere and is absorbed by plants through photosynthesis. These carbon isotopes decay at a constant rate over time, and comparing the amount of Carbon-14 in the atmosphere to the amount present in fossilized plant material allows scientists to determine their approximate age. But the plant species used, Ruppia cirrhosa grows underwater and therefore obtains much of its carbon for photosynthesis not directly from the atmosphere as terrestrial plants do, but from dissolved carbon atoms in the water.

This method is likely to give radiocarbon-based age estimates of the plant that are much older than the plants themselves. Ancient carbon enters the groundwater of the Lake Otero basin from eroded bedrock of the Tularosa Valley and the surrounding mountains, and occurs in extensive calcium carbonate deposits throughout the basin.

The authors demonstrated this effect by examining Ruppia plant material with a known age from the same region. Botanists collected living Ruppia plants from a nearby spring-fed pond in 1947 and archived them at the University of New Mexico herbarium. Using the same radiocarbon dating method, the plants that were alive in 1947 returned a radiocarbon date suggesting they were about 7400 years old, an offset resulting from the use of ancient groundwater by the plant. The authors note that if the ages of the Ruppia seeds dated from the human footprints were also offset by roughly 7400 years, their real age would be between 15 and 13 thousand years old – a date which aligns with ages of several other known early North American archaeological sites.

The dating of the footprints can be resolved through other methods, including radiocarbon dating of terrestrial plants (which use atmospheric carbon and not carbon from groundwater) and optically stimulated luminescence dating of quartz found in the sediment, the authors write.
So, a little reminder there that scientists sometime get things wrong and that radiocarbon dating needs to be done with great care, not only to remove any contamination but to ensure the sample conforms to the basic assumptions of the techniques and derived its 14C from the atmosphere and not secondary sources with a longer history of radioactive decay.

Creationists should contrast this approach with the approach of creationist frauds who, despite the 'Paluxy Tracks', which had been claimed as evidence that humans and dinosaurs co-existed, being exposed as a forgeries, still persist in trying to mislead gullible people with them to fool them into thinking that Earth is just a few thousand years old and dinosaurs were around a few thousand years ago.

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