General Science Thread

The Icelandic sagas – oral histories written down hundreds of later – tell of a leader named Leif Erikson and a settlement called “Vinland”, assumed to be coastal North America. But while it is known that the Norse landed in Canada, exactly when they set up camp to become the first Europeans to cross the Atlantic, marking the moment when the globe was first known to have been encircled by humans, has remained imprecise.

Now scientists using a new type of dating technique and taking a long-ago solar storm as their reference point have established that the settlement was occupied in AD 1021 – all by examining tree rings.

Three juniper and fir logs that were cut from the Newfoundland settlement date it to exactly a millennium ago, 471 years before Columbus’s first voyage.

It has been thought that the settlement, L’Anse aux Meadows, was thriving somewhere between 990 and 1050. This was based on stylistic analysis of architectural remains and a handful of artefacts examined after the settlement was discovered 60 years ago. The dates also tally with interpretations of the Icelandic sagas, which were written down in the 1200s

This study, published in the journal Nature, made use of the cosmic-ray induced upsurge in atmospheric radiocarbon concentrations during a known solar storm in AD 993, which released an enormous pulse of radiation that was absorbed by trees at the time.

The logs, with bark still attached, were from trees alive during that solar storm, and excavated from the site. Such solar storms are reflected in annual tree growth rings. In all three samples, 28 growth rings were formed after the one that bore evidence of the storm, meaning the trees were cut in AD 1021.

Ordinary radiocarbon dating – determining the age of organic materials by measuring their content of a particular radioactive isotope of carbon – proved too imprecise to date L’Anse aux Meadows when the site was discovered in 1960, although there was a general belief it was from the 11th century.

Proof that the trees were cut by Vikings was there, too. “They had all been modified by metal tools, evident from their characteristically clean, low-angle cuts. Such implements were not manufactured by the Indigenous inhabitants of the area at the time,” the study by scientists at the University of Groningen in the Netherlands said.

“We provide evidence that the Norse were active on the North American continent in the year AD 1021. This date offers a secure juncture for late Viking chronology. More importantly, it acts as a new point of reference for European cognisance of the Americas, and the earliest known year by which human migration had encircled the planet.”

The Vikings possessed extraordinary boat-building and navigation skills, establishing settlements on Iceland and Greenland. “Much kudos should go to these northern Europeans for being the first human society to traverse the Atlantic,” Michael Dee, a geoscientist and co-leader of the study, told Reuters.

The date corroborates two Icelandic sagas – the Saga of the Greenlanders and the Saga of Erik the Red – that recorded attempts to establish a settlement in Vinland by a leader named Leif Erikson.

Also known as Leif the Lucky, he was the son of Erik the Red, who was the founder of the first Norse settlements in Greenland. According to the Saga of the Icelanders, Leif established a Norse settlement at Vinland, which is usually interpreted as being coastal North America, though speculation remains over whether this is the L’Anse aux Meadows settlement.

“I think it is fair to describe the trip as both a voyage of discovery and a search for new sources of raw materials,” Dee said. “Many archaeologists believe the principal motivation for them seeking out these new territories was to uncover new sources of timber, in particular. It is generally believed they left from Greenland, where wood suitable for construction is extremely rare.”

The 1021 date roughly corresponds to the saga accounts, Dee said, adding: “Thus it begs the question, how much of the rest of the saga adventures are true?”

Ranga Dias, an applied physicist at the University of Rochester, who with his colleagues made the room-temperature superconductivity claim, rejects Hirsch’s allegations. He asserts that Hirsch isn’t an expert in high-pressure physics and that he has a history of claiming that the Nobel Prize–winning “BCS theory” underlying superconductivity is incorrect. Dias says Hirsch relentlessly badgers superconductivity researchers. “Hirsch is a troll,” Dias says. “We are not going to feed this troll” by providing the data.

Superconductivity is normally seen only at temperatures well below 200 K, or –73°C. But several research groups working with hydrogen-rich compounds called hydrides have claimed that they became superconductors between 200 K and 250 K when squeezed to intense pressures. Dias and his team went further. They reported that by adding a bit of carbon to precursors that make H 3 S, a known hydride superconductor, they were able to create a carbon sulfur hydride (CSH) material that pushed the superconducting temperature up to 287 K (nearly 15°C), the temperature of a cool room. The result, published in the 14 October 2020 issue of Nature, generated worldwide acclaim.

Some scientists attempted to replicate or extend the finding, without much success. And Hirsch and others raised concerns. Like other superconductors, CSH showed a characteristic plunge in electrical resistance as it dropped below the “critical temperature” (Tc) and became a superconductor. To confirm that a material superconducts, however, physicists also look for a second telltale indicator, known as the Meissner effect, in which the material expels magnetic fields below Tc.

Measuring the Meissner effect hasn’t been possible in hydrides because they are formed in minute amounts inside a high-pressure device called a diamond anvil cell (DAC), which normally is made from magnetic materials. So, hydride researchers have instead evaluated a property known as AC susceptibility, a measure of how much a material becomes magnetized in an applied magnetic field. In Dias’s Nature paper, CSH’s AC susceptibility dropped sharply at Tc, consistent with the interpretation that the material was expelling magnetic fields.

But the data also show that as the material cools below Tc, the AC susceptibility rises again. That’s a behavior not usually seen in superconductors, Hirsch argues, though others say the behavior has been seen in other superconductors under high pressure.

Hirsch also contends some of the AC susceptibility data for CSH look suspiciously similar to other data that are now in question, from a 2009 Physical Review Letters paper on superconductivity in europium under high pressure. One of that study’s authors, James Hamlin, a physicist now at the University of Florida, who participated in the europium study as a graduate student, recently determined, he says, that “there are alterations to the data.” The study’s senior author, James Schilling, an emeritus physicist at Washington University in St. Louis, says he shares that concern. Now, some of the co-authors are redoing the measurements, and if they don’t hold up, the team will retract the paper, Hamlin says.

The first author of the europium paper, Mathew Debessai, now with Intel Corporation, was responsible for the AC susceptibility measurements, and also carried out those measurements for Dias’s CSH work. And a data trace from the CSH paper looks “remarkably similar” to one from the europium paper, Hirsch contends. Schilling agrees parts of the traces do look similar, but he can’t say why. Debessai declined to respond to the questions about the data but via email wrote that he will post a formal response on the arXiv preprint server.

In October and November 2020, Hirsch emailed Dias requests for raw data. Dias replied that he would not provide the data for reasons including that his team was working to patent the work, and his lawyer advised against releasing the data. By then, Hirsch had raised concerns about the CSH data in a preprint, which was published in Nature in August. In his email to Hirsch, Dias wrote, “Given that you have an active comment on our work, we consider such a request would not be reasonable.”

Frustrated, Hirsch requested the data from Nature and the National Science Foundation (NSF), which funded the work. On 30 August, Nature appended an editor’s note to Dias’s paper saying: “The editors of Nature have been alerted to undeclared access restrictions relating to the data behind this paper. We are working with the authors to correct the data availability statement.” NSF and the University of Rochester both tell Science they cannot comment on possible investigative matters.

Then, last month in Physica C :Superconductivity and its Applications, Hirsch wrote that Dias’s anomalous AC susceptibility result, combined with seeming irregularities in the europium data, and his struggles to get the data on CSH, fed his doubts. “I suggest that one possible explanation is that [the CSH finding] is the result of data manipulation and alteration such as was described … for [europium],” Hirsch wrote.

Alexander Goncharov, a physicist at the Carnegie Institution for Science, won’t go that far, but he thinks Hirsch’s concerns about AC susceptibility measurements are fair. “I tend to believe there is a problem with the [CSH] paper,” says Goncharov, who tried repeatedly to synthesize CSH using Dias’s recipe and failed.

Given the questions, several scientists say Dias should make his data public. “I am unhappy that Dias is supposedly not cooperating with researchers who are questioning his data,” says Marvin Cohen, a theoretical physicist at UC Berkeley. Schilling is blunt: “I told Dias to give [Hirsch] the raw data, for heaven’s sake.”

Dias and others say they don’t trust Hirsch to appraise the data fairly. “Unfortunately, sometimes he is not objective,” says Vasily Minkov, a chemist at the Max Planck Institute for Chemistry who synthesizes hydride superconductors and says Hirsch has cherry-picked data from the Max Planck experiments for his critiques. Hirsch calls such critiques “completely unfounded.” Hirsch counters that his belief that the BCS theory is incorrect “does not mean I am ‘biased’ or not ‘impartial.’ It means that I am motivated to scrutinize carefully the experimental evidence and judge it on its merits, as opposed to assuming it is likely to be right because BCS theory predicts it to be right, as everybody else does.”

Several new results have only deepened the mystery. In a preprint posted on 30 September on arXiv, Goncharov’s group reports synthesizing CSH under high pressure—using a recipe different from Dias’s—and observing a crystalline structure similar to the one Dias reported. Dias sees the result as vindication, saying Goncharov’s material has the “exact structure” his team reported. But Goncharov is more cautious. His team didn’t test whether its CSH sample was superconducting. But in unpublished work, Minkov says he and his colleagues synthesized the same CSH structure as Dias’s and found it doesn’t superconduct above the Tc of H 3 S. Minkov says H 3 S may be responsible for superconductivity in his CSH sample. “We couldn’t see any effect of carbon,” he says.

Hirsch, meanwhile, is mounting a broader attack: on claims for superconductivity in any hydride. In a preprint posted on 4 October on Research Square, Minkov and a team led by Mikhail Eremets, a physicist also at Max Planck, reported remaking diamond anvil cells without magnetic materials and testing large samples of two hydrides, H 3 S and La H 10. The result: the first ever evidence of the Meissner effect in hydrides, which the team calls “unambiguous evidence” that superconductivity in hydrides is real. Hirsch disagrees, calling the analysis “deeply flawed” in a preprint he and a colleague posted on 14 October on the arXiv server.

Only one thing seems certain to emerge from the controversy over room-temperature superconductivity: more heat.

monkey puzzle trees

This is what Antarctica was like 75 million years ago during the Cretaceous period, an era known by researchers as a “super fire world.” A paper published last month in Polar Research by Flaviana Jorge de Lima of the Federal University of Pernambuco and other scientists in Brazil proves that these conflagrations did not spare any continent, even one that is today notorious for its dry, inhospitable climate and largely vegetation-free landscape.

Although research on prehistoric wildfires — properly called “paleofires” — has been going on for decades, much of it has concentrated on the Northern Hemisphere. Antarctica was “first considered a region without high fires, but that changed,” said André Jasper of the University of Taquari Valley in Brazil. He’s an author on the paper and part of a group of researchers around the globe seeking evidence of fires that burned between 60 million and 300 million years ago.

“It’s really interesting for us because now we’re showing that not only the Northern Hemisphere was burning, but the Southern Hemisphere too,” he said. “It was global.”

Scientists can find evidence of paleofires by studying charred tree rings, by analyzing sediment in ancient lakes or by examining molecules in fossilized charcoal. For this paper, the researchers analyzed charcoal extracted from sediment on Antarctica’s James Ross Island in 2015 and 2016.

This charcoal is, on its face, nothing special.

“If you do a barbecue, you will have the same type of material,” Dr. Jasper said. But the team used imaging software and scanning electron microscopy to analyze these lustrous chunks, about the height of a quarter and several times as wide. They found something far more interesting than the remains of a cookout: homogenized cells and a pitted pattern that proved these fossils started their lives as ancient plants.

Using the charcoal, “it is possible to understand a little bit better the scenario of the fire, 75 million years ago,” Dr. Jasper said.

With increasingly sophisticated techniques, scientists can reconstruct ancient ecosystems and fire patterns with mounting precision, said Elisabeth Dietze, vice president of the International Paleofire Network, who was not affiliated with the study. She said that molecular markers in charcoal could tell scientists what kind of vegetation burned: For example, rounder, plated molecular shapes indicate woody biomass.

In 2010, researchers on King George Island first gathered evidence that ancient wildfires didn’t spare Antarctica. But the samples from that expedition were poorly preserved and researchers could only speculate that the charcoal stemmed from a coniferous tree. Researchers made a more accurate assessment of these new charred remains: They suspect they came from an Araucariaceae, an ancient family of conifers.

For paleofire researchers, the next big question about these ancient fires concerns causality. The Cretaceous period was marked by mass extinctions, fluctuating amounts of oxygen in the atmosphere and changes in the amount of vegetation covering the planet. Did fires cause these changes, or did the changes cause the fires? Understanding this super fire world helps researchers develop models for periods of rapid ecological change and increasing numbers of fires — like now.

“The more we know about the past and the linkages between the ecosystem and climate, the better prepared we are for the future,” said Cathy Whitlock of Montana State University, who was not affiliated with the study.

In some ways the era humans live in can’t compare to the Cretaceous: Back then, our continents, including Antarctica, were still forming. But it’s still notable that high-latitude regions were warm, forested, ice-free and prone to blazes — a direction in which we might be moving.

“Of course, this was millions of years ago, but now we have a driver,” Dr. Jasper said. “We are the driver. Nowadays we have humans putting fire on everything.”

Case in point: In 2018, researchers moved these charcoal samples from the National Museum of Brazil to a different laboratory. A few months later, the museum caught fire and the country lost countless relics. These ancient chunks of charcoal, used to unlock the secrets of deep time, were themselves nearly lost in flames.