The double-fanged adolescence of saber-toothed cats

The fearsome, saber-like teeth of Smilodon fatalis -- California's state fossil -- are familiar to anyone who has ever visited Los Angeles' La Brea Tar Pits, a sticky trap from which more than 2,000 saber-toothed cat skulls have been excavated over more than a century.

Though few of the recovered skulls had sabers attached, a handful exhibited a peculiar feature: the tooth socket for the saber was occupied by two teeth, with the permanent tooth slotted into a groove in the baby tooth.

Paleontologist Jack Tseng, associate professor of integrative biology at the University of California, Berkeley, doesn't think the double fangs were a fluke.

Nine years ago, he joined a few colleagues in speculating that the baby tooth helped to stabilize the permanent tooth against sideways breakage as it erupted. The researchers interpreted growth data for the saber-toothed cat to imply that the two teeth existed side by side for up to 30 months during the animal's adolescence, after which the baby tooth fell out.

In a new paper accepted for publication in the journal The Anatomical Record, Tseng provides the first evidence that the saber tooth alone would have been increasingly vulnerable to lateral breakage during eruption, but that a baby or milk tooth alongside it would have made it much more stable. The evidence consists of computer modeling of saber-tooth strength and stiffness against sideways bending, and actual testing and breaking of plastic models of saber teeth.

"This new study is a confirmation -- a physical and simulation test -- of an idea some collaborators and I published a couple of years ago: that the timing of the eruption of the sabers has been tweaked to allow a double-fang stage," said Tseng, who is a curator in the UC Museum of Paleontology. "Imagine a timeline where you have the milk canine coming out, and when they finish erupting, the permanent canine comes out and overtakes the milk canine, eventually pushing it out. What if this milk tooth, for the 30 or so months that it was inside the mouth right next to this permanent tooth, was a mechanical buttress?"

He speculates that the unusual presence of the baby canine -- one of the deciduous teeth all mammals grow and lose by adulthood -- long after the permanent saber tooth erupted protected the saber while the maturing cats learned how to hunt without damaging them. Eventually, the baby tooth would fall out and the adult would lose the saber support, presumably having learned how to be careful with its saber. Paleontologists still do not know how saber-toothed animals like Smilodon hunted prey without breaking their unwieldy sabers.

"The double-fang stage is probably worth a rethinking now that I've shown there's this potential insurance policy, this larger range of protection," he said. "It allows the equivalent of our teenagers to experiment, to take risks, essentially to learn how to be a full-grown, fully fledged predator. I think that this refines, though it doesn't solve, thinking about the growth of saber tooth use and hunting through a mechanical lens."

The study also has implications for how saber-toothed cats and other saber-toothed animals hunted as adults, presumably using their predatory skills and strong muscles to compensate for vulnerable canines.

Beam theory

Thanks to the wealth of saber-toothed cat fossils, which includes many thousands of skeletal parts in addition to skulls, unearthed from the La Brea Tar Pits, scientists know a lot more about Smilodon fatalis than about any other saber-toothed animal, even though at least five separate lineages of saber-toothed animals evolved around the world. Smilodon roamed widely across North America and into Central America, going extinct about 10,000 years ago.

Yet paleontologists are still confounded by that fact that adult animals with thin-bladed knives for canines apparently avoided breaking them frequently despite the sideways forces likely generated during biting. One study of the La Brea predator fossils found that during periods of animal scarcity, saber-toothed cats did break their teeth more often than in times of plenty, perhaps because of altered feeding strategies.

The double-fanged specimens from La Brea, which have been considered rare cases of individuals with delayed loss of the baby tooth, gave Tseng a different idea -- that they had an evolutionary purpose. To test his hypothesis, he used beam theory -- a type of engineering analysis employed widely to model structures ranging from bridges to building materials -- to model real-life saber teeth. This is combined with finite element analysis, which uses computer models to simulate the sideways forces a saber tooth could withstand before breaking.

"According to beam theory, when you bend a blade-like structure laterally sideways in the direction of their narrower dimension, they are quite a lot weaker compared to the main direction of strength," Tseng said. "Prior interpretations of how saber tooths may have hunted use this as a constraint. No matter how they use their teeth, they could not have bent them a lot in a lateral direction."

He found that while the saber's bending strength -- how much force it can withstand before breaking -- remained about the same throughout its elongation, the saber's stiffness -- its deflection under a given force -- decreased with increasing length. In essence, as the tooth got longer, it was easier to bend, increasing the chance of breakage.

By adding a supportive baby tooth in the beam theory model, however, the stiffness of the permanent saber kept pace with the bending strength, reducing the chance of breaking.

"During the time period when the permanent tooth is erupting alongside the milk one, it is around the time when you switch from maximum width to the relatively narrower width, when that tooth will be getting weaker," Tseng said. "When you add an additional width back into the beam theory equation to account for the baby saber, the overall stiffness more closely aligned with theoretical optimal."

Though not reported in the paper, he also 3D-printed resin replicas of saber teeth and tested their bending strength and stiffness on a machine designed to measure tensile strength. The results of these tests mirrored the conclusions from the computer simulations. He is hoping to 3D-print replicas from more life-like dental material to more accurately simulate the strength of real teeth.

Tseng noted that the same canine stabilization system may have evolved in other saber-toothed animals. While no examples of double fangs in other species have been found in the fossil record, some skulls have been found with adult teeth elsewhere in the jaws but milk teeth where the saber would erupt.

"What we do see is milk canines preserved on specimens with otherwise adult dentition, which suggests a prolonged retention of those milk canines while the adult tooth, the sabers, are either about to erupt or erupting," he said.

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Study explores impacts of Arctic warming on daily weather patterns in the U.S.

Arctic sea ice is shrinking as the world continues to warm, and a new study led by researchers at Penn State may provide a better understanding of how the loss of this ice may impact daily weather in the middle latitudes, like the United States.

The researchers used climate models and a machine learning approach to tease out the impacts of ice sea loss on the future of large-scale meteorological patterns over North America. They reported in the Journal of Climate that ice sea loss de-amplified these patterns and their impacts on temperature near the surface -- meaning, for example, cold weather events may be less cold.

"The Arctic in general is the source of cold air for us when we have these really cold events," said Melissa Gervais, assistant professor in the Department of Meteorology and Atmospheric Science at Penn State and lead author of the study. "As warming continues, we know that the Arctic is going to be less cold. What this work shows us is that the loss of sea ice also changes weather patterns that bring cold air to the middle latitudes. So, warming both depletes your source of cold air and makes it harder to transport."

Sea ice acts like a blanket over the ocean, keeping warmer water from losing heat to the atmosphere, Gervais said. Once the ice is gone, heat from the ocean can enter the atmosphere and create a low-pressure system over where the ice had been, resulting in less transport of cold Arctic air to other parts of Earth, the scientists said.

As sea ice melts, the Arctic is warming at a faster rate than the rest of the planet, a process called Arctic amplification. And while it would be expected that less cold air would be transported from the Arctic to the middle latitudes under these conditions, the new study allowed the researchers to probe more deeply into the mechanisms responsible for these changes.

"Our research allowed us to dig a little bit deeper into what is going on," Gervais said. "We were able to see that in addition to the impact of Arctic amplification, there also is an impact on the actual circulation or flow in the atmosphere."

To test the impact on weather patterns, the scientists ran a climate model under two scenarios -- one with ice levels consistent with the 1980s and 1990s, and the other with reduced ice levels expected by the end of the century.

They used self-organizing maps, a machine learning method, to classify patterns of daily weather in the troposphere, the lowest layer of Earth's atmosphere where most weather occurs. They then explored how those general weather patterns translate into variables that are closer to the surface.

"Without using this machine learning method, we would not have been able to really robustly understand the processes involved," Gervais said. "For studies like this, where we're using a large volume of climate model simulations, we can't find these patterns by hand."

One weather pattern particularly impacted by the loss of sea ice involved cold weather anomalies over North America. The pattern is associated with strong cold anomalies, which reached roughly 29 degrees Fahrenheit under current sea ice conditions but warmed significantly under the scenarios with less sea ice, the scientists said.

"We found that when we lose sea ice, not only is that anomaly reduced, but it also actually becomes a warm pattern," Gervais said. "So, the same pattern in the upper atmosphere is now actually bringing warmer temperatures near the surface."

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US air pollution rates on the decline but pockets of inequities remain

Over the last decades, air pollution emissions have decreased substantially; however, the magnitude of the change varies by demographics, according to a new study by Columbia University Mailman School of Public Health. The results indicate there are racial/ethnic and socioeconomic disparities in air pollution emissions reductions, particularly in the industry and energy generation sectors. The findings are published in the journal Nature Communications.

The research provides a national investigation of air pollution emission changes in the 40 years following the enactment of the Clean Air Act (CAA). Until now, studies have primarily focused on evaluating air pollution disparities at a single time point, focusing on pollutant concentrations instead of emissions. A focus on emissions, however, has more direct implications for regulations and policies. In this study, the researchers used county-level data to evaluate racial/ethnic and socioeconomic disparities in air pollution emissions changes in the contiguous U.S. from 1970 to 2010.

"The analyses provide insight on the socio-demographic characteristics of counties that have experienced disproportionate decreases in air pollution emissions over the last forty years," said Yanelli Nunez, PhD, the study's first author, who is a scientist in the Department of Environmental Health Sciences at Columbia Mailman School of Public Health and affiliated with PSE Healthy Energy. Additionally, by analyzing air pollution emissions, the researchers identified specific pollution source sectors that are potentially important contributors to air pollution exposure disparities.

Nunez and colleagues leveraged air pollution emissions data from the Global Burden of Disease Major Air Pollution Sources inventory to analyze air pollutant emissions from six pollution source sectors: industry (sulfur dioxide), energy (sulfur dioxide and nitrogen oxides), agriculture (ammonia), on-road transportation (nitrogen oxides), commercial (nitrogen oxides), and residential (particles of organic carbon).

On average, national U.S. air pollution emissions declined substantially from 1970 to 2010 from all source sectors the researchers considered except for ammonia emissions from agriculture and organic carbon particle emissions from the residential sector, which the researchers indicate is primarily from using solid biofuels for indoor heating. The most pronounced emission decreases were observed for sulfur dioxidefrom industrial and energy generation activities. Nitrogen oxide emissions from transportation, commercial activities, and energy generation decreased moderately.

Despite the overall downward trends for most pollutants, the researchers found that certain populations experienced relatively smaller reductions or even increases in air pollution emissions. For instance, an increase in a county's average Hispanic or Indian American population percentage resulted in a relative increase in sulfur dioxide, nitrogen oxides, and ammonia emissions from the industry, energy generation, and agriculture sectors, respectively. Additionally, an increase in the county median family income was linked with an increase in the magnitude of emissions reductions in every pollution source sector the researchers analyzed, except agriculture.

"Air pollution emissions do not perfectly capture population air pollution exposure, and we also know that neighborhood-level air pollution inequities are common, which we were not able to analyze in this study given the data at hand," noted Marianthi-Anna Kioumourtzoglou, ScD, associate professor of environmental health sciences at Columbia Mailman School, and senior author. "In this study, we provide information about potential racial/ethnic and socioeconomic inequalities in air pollution reductions nationwide from major air pollution sources, which can inform regulators and complement local-level analysis."

"Policies specifically targeting reductions in overburdened populations could support more just reductions in air pollution and reduce disparities in air pollution exposure," observed Dr. Nunez. "This is an important lesson gained from 53 years of Clean Air Act implementation, which is particularly relevant as we develop policies to transition to renewable energy sources, which will have a collateral impact on air quality and, as a result, on public health."

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Cracking the code: Genome sequencing reveals why songbirds are larger in colder climates

Scientists have unlocked the genetic basis underlying the remarkable variation in body size observed in song sparrows, one of North America's most familiar and beloved songbirds. This discovery also provides insights into this species' capacity to adapt to the challenges of climate change.

The study, published today in Nature Communications, used genomic sequencing to successfully pinpoint eight genetic variants, or DNA mutations, largely responsible for the nearly threefold difference in body size observed across the song sparrow range from Mexico to Alaska. For instance, song sparrows that live year-round in the Aleutian Islands can be up to three times larger than their counterparts in the coastal marshes of California.

Katherine Carbeck, the study's first author and a PhD candidate in the faculty of forestry, University of British Columbia, explains that body size varies predictably in many species that inhabit vastly different climatic conditions, aligning with "Bergmann's rule" which states that organisms in cooler climates tend to be larger as an adaptation to regulate body temperature.

"The existence of 'locally adapted' populations implies that natural selection has shaped the genetic makeup of song sparrow populations across their range, enabling individuals to survive and reproduce in drastically different climatic conditions," said Carbeck. "However, the genetic mechanisms underlying Bergmann's rule have remained elusive until now."

Whole-genome sequencing cracks the code

Carbeck and colleagues from the Cornell Lab of Ornithology, University of Alaska and Ouachita Baptist University used the power of whole-genome sequencing to decode the entire song sparrow genome and unlock its secrets.

They combed through genetic samples from the two largest song sparrow subspecies that live year-round in the Aleutian Islands, as well as two smaller subspecies: one that breeds in Alaska but migrates to warmer sites in winter, and one that lives year-round on the B.C. coast, where the Pacific Ocean maintains comparatively mild winter weather.

Their comparison of the larger and smaller-bodied subspecies revealed several candidate genes associated with body mass. By characterizing these candidates, they identified eight specific genetic variants closely linked to body mass -- aligning with Bergmann's rule.

Genetic diversity helps life adapt to climate change

The researchers suggest that revealing a genetic basis for Bergmann's rule helps us to understand how evolution, natural selection and climate have interacted throughout a species' history.

"Our results highlight the potential role habitat conservation plays in enabling the continued exchange of genes between populations -- which is important in the face of ongoing change," said Carbeck.

Dr. Jen Walsh, a study co-author and research associate at the Cornell Lab of Ornithology, added: "From a genomic perspective, identifying a small number of candidate genes with an apparently large impact on variation in body size is really interesting. The magnificent range of phenotypic diversity seen in song sparrows suggest they offer exciting opportunities to identify genes underlying a host of well-known and generally accepted eco-geographic rules."

Dr. Peter Arcese, a co-author and a professor in UBC's department of forest and conservation sciences, said the findings suggest a resilient future for these birds.

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Fossils tell tale of last primate to inhabit North America before humans

The story of Ekgmowechashala, the final primate to inhabit North America before Homo sapiens or Clovis people, reads like a spaghetti western: A grizzled and mysterious loner, against the odds, ekes out an existence on the American Plains.

Except this tale unfolded about 30 million years ago, just after the Eocene-Oligocene transition during which North America saw great cooling and drying, making the continent less hospitable to warmth-loving primates.

Today, paleontologists from the University of Kansas and the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing have published evidence in the Journal of Human Evolution shedding light on the long-standing saga of Ekgmowechashala, based on fossil teeth and jaws found in both Nebraska and China.

To do so, the researchers first had to reconstruct its family tree, a job helped by the discovery of an even more ancient Chinese "sister taxon" of Ekgmowechashala the team has named Palaeohodites (or "ancient wanderer"). The Chinese fossil discovery resolves the mystery of Ekgmowechashala's presence in North America, showing it was an immigrant rather than the product of local evolution.

"This project focuses on a very distinctive fossil primate known to paleontologists since the 1960s," said lead author Kathleen Rust, a doctoral candidate in paleontology at KU's Biodiversity Institute and Natural History Museum. "Due to its unique morphology and its representation only by dental remains, its place on the mammalian evolutionary tree has been a subject of contention and debate. There's been a prevailing consensus leaning towards its classification as a primate. But the timing and appearance of this primate in the North American fossil record are quite unusual. It appears suddenly in the fossil record of the Great Plains more than 4 million years after the extinction of all other North American primates, which occurred around 34 million years ago."

In the 1990s, Rust's doctoral adviser and co-author Chris Beard, KU Foundation Distinguished Professor and senior curator of vertebrate paleontology, collected fossils from the Nadu Formation in the Baise Basin in Guangxi, China, that closely resembled the Ekgmowechashala material known from North America. By that time, Ekgmowechashala was notoriously enigmatic among North American paleontologists.

"When we were working there, we had absolutely no idea that we would find an animal that was closely related to this bizarre primate from North America, but literally as soon as I picked up the jaw and saw it, I thought, 'Wow, this is it,'" Beard said. "It's not like it took a long time, and we had to undertake all kinds of detailed analysis -- we knew what it was. Here in KU's collection, we have some critical fossils, including what is still by far the best upper molar of Ekgmowechashala known from North America. That upper molar is so distinctive and looks quite similar to the one from China that we found that it kind of seals the deal."

Beard left it to Rust to conduct the morphological analysis that tied Ekgmowechashala and its cousin Palaeohodites from China in a phylogenetic tree to establish their evolutionary relationships.

In the course of the work, Rust was able to draw conclusions about how Ekgmowechashala came to be discovered in Nebraska, millions of years after its fellow primates died out in the continent's fossil record.

"We collected a substantial amount of morphological data to create an evolutionary tree using a phylogenetic reconstruction software and algorithm," Rust said. "This evolutionary tree suggests a close evolutionary relationship between North American Ekgmowechashala and Palaeohodites from China, which Chris and his colleagues discovered in the 1990s. The results from our analysis unequivocally supports this hypothesis."

The KU researchers said their discovery is not only exciting in terms of discovering a new primate species from late Eocene China -- but also in settling the origin story of Ekgmowechashala. Based on their investigation, Ekgmowechashala did not descend from an older North American primate that somehow survived the cooler and drier conditions that caused other North American primates to go extinct. Rather, its ancestors crossed over the Beringian region millions of years later, anticipating the route followed by the first Native Americans much later in time.

"Our analysis dispels the idea that Ekgmowechashala is a relic or survivor of earlier primates in North America," Rust said. "Instead, it was an immigrant species that evolved in Asia and migrated to North America during a surprisingly cool period, most likely via Beringia."

Species like Ekgmowechashala that show up suddenly in the fossil record long after their relatives have died off are referred to as "Lazarus taxa" after the biblical figure who was raised from the dead.

"The 'Lazarus effect' in paleontology is when we find evidence in the fossil record of animals apparently going extinct -- only to reappear after a long hiatus, seemingly out of nowhere," Beard said. "This is the grand pattern of evolution that we see in the fossil record of North American primates. The first primates came to North America about 56 million years ago at the beginning of the Eocene, and they flourished on this continent for more than 20 million years. But they went extinct when climate became cooler and drier near the Eocene-Oligocene boundary, about 34 million years ago. Several million years later Ekgmowechashala shows up like a drifting gunslinger in a Western movie, only to be a flash in the pan as far as the long trajectory of evolution is concerned. After Ekgmowechashala is gone for more than 25 million years, Clovis people come to North America, marking the third chapter of primates on this continent. Like Ekgmowechashala, humans in North America are a prime example of the Lazarus effect."

Rust and Beard were joined in the work by co-authors Xijun Ni of the Chinese Academy of Sciences, Beijing, and Kristen Tietjen, scientific illustrator with the KU Biodiversity Institute and Natural History Museum.

According to Rust, the tale of Ekgmowechashala is worth people's attention because it happened in an era of profound environmental and climatic changes, much like our own that's driven by human activity.

"It's crucial to comprehend how past biota reacted to such shifts," she said. "In such situations, organisms typically either adapt by retreating to more hospitable regions with available resources or face extinction. Around 34 million years ago, all of the primates in North America couldn't adapt and survive. North America lacked the necessary conditions for survival. This underscores the significance of accessible resources for our non-human primate relatives during times of drastic climatic change."

The study is also a part of a larger story that represents the earliest chapters of our own evolutionary journey that ultimately led to our own species, Rust said.

Read more at Science Daily

75% of exclusive hardwood may be illegally harvested

The tropical wood type ipê is popular for building exclusive wooden decks, and in North America and Europe, the demand for the material has increased sharply. Now, a study from Chalmers University of Technology, Sweden, shows that more than three-quarters of all ipêfrom the top producing region in Brazil could have been harvested illegally. "The study reveals where in the chain the greatest risks lie. It can be a tool to counteract illegal logging," says Caroline S.S. Franca, PhD student at Chalmers.

Ipê is one of the world's hardest woods. It is therefore particularly suitable for building balconies, conservatories, stairs or piers. Demand for the exclusive, tropical wood has increased steadily in recent years, especially on European, American and Canadian markets. In Brazil, the country of origin for 96 percent of all ipê on the market, exports have increased by over 76 percent in volume over the past decade.

This development means an increased risk of illegal logging of ipê, which in November 2022 was included on the Cites list of species threatened by overexploitation due to its popularity and increasing demand through international trade.

"Some products from the rainforest are more valuable and therefore more vulnerable to illegal logging. Ipê is at the top of that list. At the same time, ipê trees grow slowly, which means that regrowth takes a long time. The risk of extinction is real, and today there are no reliable figures on the amount of remaining trees and the damage to existing stands that has already been done," says Caroline S.S. Franca, PhD student in Physical Resource Theory at Chalmers.

Mapping where risks are greatest

Caroline S.S. Franca is the lead author of a research study on the risks for illegal logging of ipê in Brazil, which was recently published in Nature Sustainability. In the study, the researchers analysed extensive amounts of data to identify where in the supply chains there are significant risks that logging has taken place illegally.

The conclusion is that more than three-quarters of all ipê from Pará -- the top producing state of this wood in Brazil and a major source of exports -- in the period 2009-2019 may have been illegally harvested.

"In the study, we see, for example, that 16 percent of the ipê that ends up on the market is harvested without proper permits, and that landowners claim that they have felled more ipê on their land than is likely to exist on the stated area. We also show that there is more wood in circulation than the official production figures indicate," she says.

Paving the way for better enforcement and practices

"We know that illegal logging is driving forest degradation, and is linked to organised crime, conflict and the destruction of forest-dependent local communities," continues Caroline S.S. Franca, adding that "degradation of Amazon forests does not only affect the local environment and the ecological diversity of the rainforest, it is also as large of a contributor to climate change as outright deforestation."

She hopes that her research results can contribute to an increased awareness of the extent of illegal logging among decision-makers and actors in the supply chain, as well as among consumers.

"The novel methods developed in the study, exploring existing patterns in the data for transactions and approvals of ipê exploration have an enormous potential both to improve forest control systems in Brazil, as well as to support supply-chain actors in their efforts to make timber sourcing more responsible and sustainable," says Marco Lentini, a co-author of the study with a long-standing experience working on sustainable forest management in the Brazilian Amazon.

The information already exists, now there is political will to use it

Recent numbers form Brazil's forest monitoring system shows that deforestation in the Amazon have been almost halved in 2023, compared to last year. Brazilian President Luiz Inácio Lula da Silva also initiated the so-called Belém Declaration -- an alliance among eight South American countries to combat the deforestation of the Amazon, adopted on August 8, 2023.

"This declaration is a welcome expression of renewed political will to reduce deforestation," comments Martin Persson, co-author of the ipê study and a Chalmers researcher with extensive experience of research on the devastation of the Amazon.

But he also emphasises that the danger is far from over, and that the declaration itself will not lead to change.

"Halting deforestation and forest degradation requires concrete policy measures. And what we point out in our study is that there is already data and information that can be used by authorities to get to those who harvest forests illegally," he says.

Important for consumers to ask questions

There is a certification for sustainably produced wood, FSC, which can serve as a guide for consumers who want to avoid buying non-sustainable or illegally harvested wood. But regardless of whether the wood has an FSC certification or not, Caroline S.S. Franca emphasises that it is always important to ask a few basic questions before buying.

"Where exactly does the wood come from? Is there documentation of the origin of the wood and its path through the production chain? As a consumer, you have a greater opportunity to make an informed decision if you get answers to those questions," she says.

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Oldest fossil human footprints in North America confirmed

The 2021 results began a global conversation that sparked public imagination and incited dissenting commentary throughout the scientific community as to the accuracy of the ages.

"The immediate reaction in some circles of the archeological community was that the accuracy of our dating was insufficient to make the extraordinary claim that humans were present in North America during the Last Glacial Maximum. But our targeted methodology in this current research really paid off," said Jeff Pigati, USGS research geologist and co-lead author of a newly published study that confirms the age of the White Sands footprints.

The controversy centered on the accuracy of the original ages, which were obtained by radiocarbon dating. The age of the White Sands footprints was initially determined by dating seeds of the common aquatic plant Ruppia cirrhosa that were found in the fossilized impressions. But aquatic plants can acquire carbon from dissolved carbon atoms in the water rather than ambient air, which can potentially cause the measured ages to be too old.

"Even as the original work was being published, we were forging ahead to test our results with multiple lines of evidence," said Kathleen Springer, USGS research geologist and co-lead author on the current Science paper. "We were confident in our original ages, as well as the strong geologic, hydrologic, and stratigraphic evidence, but we knew that independent chronologic control was critical."

For their follow-up study, the researchers focused on radiocarbon dating of conifer pollen, because it comes from terrestrial plants and therefore avoids potential issues that arise when dating aquatic plants like Ruppia. The researchers used painstaking procedures to isolate approximately 75,000 pollen grains for each sample they dated. Importantly, the pollen samples were collected from the exact same layers as the original seeds, so a direct comparison could be made. In each case, the pollen age was statistically identical to the corresponding seed age.

"Pollen samples also helped us understand the broader environmental context at the time the footprints were made," said David Wahl, USGS research geographer and a co-author on the current Science article. "The pollen in the samples came from plants typically found in cold and wet glacial conditions, in stark contrast with pollen from the modern playa which reflects the desert vegetation found there today."

In addition to the pollen samples, the team used a different type of dating called optically stimulated luminescence, which dates the last time quartz grains were exposed to sunlight. Using this method, they found that quartz samples collected within the footprint-bearing layers had a minimum age of ~21,500 years, providing further support to the radiocarbon results.

With three separate lines of evidence pointing to the same approximate age, it is highly unlikely that they are all incorrect or biased and, taken together, provide strong support for the 21,000 to 23,000-year age range for the footprints.

Read more at Science Daily

Newly discovered 'primitive cousins of T rex' shed light on the end of the age of dinosaurs in Africa

Fossils of primitive cousins of T. rex that had short, bulldog snouts and even shorter arms have been discovered by scientists in Morocco. The two new dinosaur species belong to the Abelisauridae, a family of carnivorous dinosaurs that were counterparts to the tyrannosaurs of the Northern Hemisphere. They lived at the end of the Cretaceous period and show that dinosaurs were diverse in Africa just before their mass extinction by an asteroid 66 million years ago.

Two new species of dinosaur have been found from the end of the Cretaceous in Morocco, just outside of Casablanca. One species, found near the town of Sidi Daoui, is represented by a foot bone from a predator about two and a half metres (eight feet) long. The other, from nearby Sidi Chennane, is the shin bone of a carnivore that grew to around five metres (15 feet) in length.

Both were part of a family of primitive carnivorous dinosaurs known as abelisaurs, and lived alongside the much larger abelisaur Chenanisaurus barbaricus, showing that Morocco was home to diverse dinosaur species just before a giant asteroid struck at the end of the Cretaceous, ending the age of dinosaurs.

Dr Nick Longrich, from the Milner Centre for Evolution at the University of Bath, led the study. He said: "What's surprising here is that these are marine beds.

"It's a shallow, tropical sea full of plesiosaurs, mosasaurs, and sharks. It's not exactly a place you'd expect to find a lot of dinosaurs. But we're finding them."

Even though dinosaurs account for a small proportion of the fossils, the region is so rich in fossils, it has produced the best picture of African dinosaurs from the end of the age of dinosaurs.

Rather than finding the same few species, palaeontologists often recover fossils from new species, suggesting the beds host an extremely diverse dinosaur fauna.

So far, the small number of dinosaur fossils that have been recovered represent five different species -- a small duckbill dinosaur named Ajnabia, a long-necked titanosaur, the giant abelisaur Chenanisaurus, and now the two new abelisaurs.

Dr Longrich said: "We have other fossils as well, but they're currently under study. So we can't say much about them at the moment, except that this was an amazingly diverse dinosaur fauna."

The last dinosaurs vanished around 66 million years ago, along with as much as 90% of all species on earth, including mosasaurs, plesiosaurs, pterosaurs and ammonites. The pattern of the end-Cretaceous extinction and its causes have been debated for over two hundred years.

A giant asteroid impact in the Yucatan peninsula has been linked to their demise, although it's been argued that dinosaurs were already in decline. The Moroccan dinosaurs suggest that they thrived in North Africa up to the very end.

"The end of the Cretaceous in western North America definitely seems to become less diverse at the end," said Longrich. "But that's just one small part of the world. It's not clear that you can generalise from the dinosaurs of Wyoming and Montana to the whole world.

"It also grew colder near the end, so it might not be surprising if dinosaurs at higher latitudes became less diverse. But we don't know much about dinosaurs from lower latitudes."

In Morocco at least, they seem to have remained diverse and successful up until the end.

"When T. rex reigned as a megapredator in North America, abelisaurs sat at the top of the food chains in North Africa," said Nour-Eddine Jalil, a professor at the Natural History Museum and a researcher at Universite Cadi Ayyad in Morocco, who was a co-author on the paper.

"The dinosaur remains, despite their rarity, give the same messages as the more abundant marine reptile remains.

"They tell us that, just before the Cretaceous-Paleogene crisis, biodiversity was not declining but on the contrary, was diverse."

Read more at Science Daily

Marine fossils unearth story about Panama's deep past

Between 6.4 and 5.8 million years ago, most of the land bridge that connects North and South America had already emerged and the channels connecting both Pacific and Atlantic oceans were shallow. Recent fossil discoveries in the northern Panama Canal area suggest that marine species interchange persisted across these shallow waters during the final stages of formation of the isthmus.

In 2017 and 2019, Aldo Benites-Palomino was studying fossils collected in Caribbean Panama, when he came across some unexpected specimens. He was a biology student in Perú, where his training had been very classical. As an intern and later a fellow at the Smithsonian Tropical Research Institute (STRI), his mindset shifted. His mentor, STRI staff scientist and paleobiologist Carlos Jaramillo, encouraged his students to change their focus when looking at fossils: instead of thinking about specimens or methods, to think about the questions that the fossils could help answer.

"I wanted to go to STRI because it is the most important tropical biology center in the world," said Benites-Palomino. "There I was able to learn a lot about the way biology and ecology is done in the modern world."

The fossil remains belonged to small-sized cetaceans, a group of aquatic mammals that includes whales and dolphins, and the specimens were new for the region. Most of them had been collected by Carlos de Gracia from STRI and Jorge Velez Juarbe from the Los Angeles Museum of Natural History, both co-authors in a new paper published in Biology Letters. In the article, Benites-Palomino and his colleagues go beyond describing the specimens, they also unearth the story they reveal about the isthmus' deep past.

The fossils belonged to the Late Miocene, around 6.4 to 5.8 million years ago, when the final stages of formation of the isthmus had already started. This event affected oceanic waters and marine currents across the globe and triggered speciation events, where species separated by the land bridge developed their own unique characteristics on either ocean.

However, these cetaceans found in Caribbean Panama shared similarities with other Late Miocene species from the North and South Pacific Ocean, particularly the Pisco Formation in Peru, suggesting that some organisms were still able to disperse via the shallowing seaway at a time when deep water interchange between both oceans was no longer occurring.

The lack of fossil marine mammals from the western Caribbean has thus far hampered understanding of the region's deep past, so these new findings help strengthen current knowledge regarding the connectivity between the Pacific and Caribbean marine faunas during the final phases of formation of the isthmus.

Read more at Science Daily

Fewer teens now perceive themselves as overweight -- international study of more than 745,000 adolescents

A study involving more than 745,000 adolescents from 41 countries across Europe and North America identified an increase in the amount of teenagers who underestimate their body weight.

Tracking data from 2002 to 2018, the peer-reviewed findings, published today in Child and Adolescent Obesity, demonstrate a noticeable decrease in those who overestimate their weight too.

The team of international experts, who carried out the research, warn these shifting trends in body weight perception could reduce the effectiveness of public health interventions aimed at weight reduction in young people.

"During this impressionable age, body weight perception may influence a young person's lifestyle choices, such as the amount and types of food they eat and their exercise habits," says lead author Doctor Anouk Geraets, from the Department of Social Sciences, at the University of Luxembourg.

"So it's concerning that we're seeing a trend where fewer adolescents perceive themselves as being overweight -- as this could undermine ongoing efforts to tackle increasing levels of obesity in this age group. Young people who underestimate their weight and therefore do not consider themselves to be overweight may not feel they need to lose excess weight and, as a result, they may make unhealthy lifestyle choices."

A person's perception of their body weight may not accurately reflect their actual weight. A discrepancy in body weight perception (BWP) may either be an underestimation (where actual weight is higher than perceived weight) or an overestimation (where actual weight is lower than perceived weight).

In the present study, the researchers examined survey data from 746,121 11-, 13- and 15-year-olds from 41 countries collected at four-yearly intervals between 2002 and 2018 in the International Health Behavior in School-Aged Children (HBSC), a WHO collaborative study.

The team modeled trends in BWP among adolescents across different countries over time, making adjustments for age, gender, and family socioeconomic status. They found:

•     Underestimation of weight status increased, and overestimation of weight status decreased over time among both sexes, with stronger trends for girls.
•     Correct weight perception increased over time among girls, while it decreased among boys.
•     Changes in correct weight perception, underestimation and overestimation of weight status differed across different countries -- but these changes could not be explained by an increase in country-level overweight/obesity prevalence.

The authors speculated that the observed differences between girls and boys in BWP may support the idea there are sex differences in body ideals -- and that these body ideals have changed over time. Notably, the increased underestimation and decreased overestimation of weight status over time for girls may be explained by the emergence of an athletic and strong body, as a new contemporary body ideal for both sexes.

"This study has clinical and public health implications. The increase in correct weight perception and the decrease in overestimation may have a positive effect on unnecessary and unhealthy weight loss behaviors among adolescents, while the increase in underestimation might indicate the need for interventions to strengthen correct weight perception," says lead author Doctor Anouk Geraets.

"More research is now needed to understand the factors underlying these time trends and to develop effective public health interventions."

Read more at Science Daily

Joro spiders aren't scary: They're shy

Despite their intimidating appearance, the giant yellow and blue-black spiders spreading across the Southeastern U.S. owe their survival to a surprising trait: They're rather timid.

According to a new study from the University of Georgia, the Joro spider may be the shyest spider ever documented.

"One of the ways that people think this spider could be affecting other species is that it's aggressive and out-competing all the other native spiders," said Andy Davis, lead author of the study and a research scientist in UGA's Odum School of Ecology. "So we wanted to get to know the personality of these spiders and see if they're capable of being that aggressive.

"It turns out they're not."

The researchers compared more than 450 spiders' responses to a brief and harmless disturbance across 10 different species.

While most spiders froze for less than a minute before resuming their normal activities, the Joro spiders remained motionless for more than an hour.

"They basically shut down and wait for the disturbance to go away," Davis said. "Our paper shows that these spiders are really more afraid of you than the reverse."

In fact, Joros are relatively harmless to people and pets. Joros won't bite unless cornered. And even if you did manage to somehow annoy a Joro into biting you, its fangs likely wouldn't be large enough to pierce your skin.

Most spiders begin moving quickly after stress, Joros remain immobile for 60+ minutes

To examine the spiders' reaction to stress, the researchers used a turkey baster to gently blow two rapid puffs of air onto individual spiders. This minor disturbance causes the spiders to "freeze" for a period of time, going absolutely still.

The researchers tested more than 30 garden spiders, banded garden spiders and marbled orb weavers. They also analyzed similar data from previously published, peer-reviewed papers that assessed the response of 389 more spiders, comprising five additional species.

All of those spiders began moving again after an average of about a minute and half of stillness.

The Joros, however, stayed frozen with no body or leg movement for over an hour in most cases.

The only other spider species that exhibited a similarly extended response was the Joro spider's cousin, the golden silk spider. Known as Trichonephila clavipes, the golden silk spider and the Joro spider are from the same genus.

Joros may be invasive, but they're not aggressive

Officially known as Trichonephila clavata, the East Asian Joro spider first arrived in Georgia around 2013. The species is native to Japan, Korea, Taiwan and China, and likely hitched a ride stateside on a shipping container.

The species has since rapidly spread across the state and much of the Southeast. Joro spiders easily number in the millions now. And there's not much we can do to stop them from increasing their range.

Davis' previous research even suggested the invasive arachnids could spread beyond their current habitats and through most of the Eastern Seaboard.

"Most people think 'invasive' and 'aggressive' are synonymous," said Amitesh Anerao, co-author of the study and an undergraduate researcher at the university. "People were freaking out about the Joro spiders at first, but maybe this paper can help calm people down."

Joro spiders built to withstand human activity

Joros are regularly spotted in areas native Georgia spiders don't typically inhabit.

They build their golden webs between powerlines, on top of stoplights and even above the pumps at local gas stations -- none of which are particularly peaceful spots.

The researchers believe the Joro spiders' shyness may help them better endure the barrage of noise, vibrations and visual stimuli they consistently encounter in urban settings. Their prolonged freeze response to being startled could help conserve the Joro spiders' energy.

If you're wondering how something so mild-mannered could spread the way Joro spiders have, you aren't the only one.

"One thing this paper tells me is that the Joros' rapid spread must be because of their incredible reproductive potential," Davis said. "They're simply outbreeding everybody else. It's not because they're displacing native spiders or kicking them out of their own webs."

Read more at Science Daily

Do your homework to prep for the 2023 and 2024 eclipses

This year and next, Americans will have the extraordinary opportunity to witness two solar eclipses as both will be visible throughout the continental U.S. On Oct. 14, 2023, the moon will obscure all but a small annulus of the sun, producing a "ring of fire" eclipse. On April 8, 2024, the eclipse will be total in a band stretching from Texas to Maine.

Both occurrences promise to be remarkable events and teachable moments. But preparation is essential.

In The Physics Teacher, co-published by AIP Publishing and the American Association of Physics Teachers, astronomer Douglas Duncan of the University of Colorado provides a practical playbook to help teachers, students, and the general public prepare for the eclipse events. He also shares ways to fundraise for schools and organizations and guidance for safe eclipse-viewing. The Fiske Planetarium, which Duncan used to direct, is also producing short videos about the upcoming eclipses.

"According to NASA surveys, over 100 million Americans watched the 2017 eclipse in person or via media," said Duncan. "That was when a total eclipse crossed the U.S., with totality viewable in Wyoming, where Motel 6 rooms in the state were going for $800 a night if you didn't book far in advance. A total eclipse is worth traveling to. It is incredible, and people remember it their whole life."

A self-described eclipse-chaser who has himself witnessed 12 eclipses beginning in 1970, Duncan emphasizes the importance of eye protection. He cites two companies that produce inexpensive glasses for viewing the sun and advises event organizers to order them well in advance: Solar Eclipse Glasses and Rainbow Symphony.

Additionally, after observing spectators at previous eclipses using their phones to snap pictures, Duncan developed Solar Snap, a filter and app to enable safe and effective smart phone photography for such events.

With small groups, Duncan suggests using binoculars to project an image of the sun so that viewers can safely observe the spectacle transposed onto a sheet of paper.

Read more at Science Daily

New look at climate data shows substantially wetter rain and snow days ahead

A key source of information underpinning the upcoming National Climate Assessment suggests that heavy precipitation days historically experienced once in a century by Americans could in the future be experienced on several occasions in a lifetime.

Scientists at Scripps Institution of Oceanography at UC San Diego and the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) report that extremely intense days of rain or snow will be more frequent by the end of this century than previously thought -- as often as once every 30 or 40 years in the Pacific Northwest and southeastern United States.

The conclusions come from analyzing a 30-terabyte data set that models temperature and precipitation at scales roughly the size of urban ZIP codes: six kilometers (3.9 miles). Researchers developed the data set, called Localized Constructed Analogs Version 2 (LOCA2), to provide climate information that is useful for local planners. In contrast, most of the existing advanced climate models look at regions that range from 50 to 250 kilometers (30 to 400 miles).

"With this data set, we're able to look at the impacts of actual weather pattern changes across the United States at an extremely granular level," said Dan Feldman, staff scientist at Berkeley Lab and the project's principal investigator. "We see that there is a lot more extreme weather that is likely to happen in the future -- and by looking at actual weather patterns, we show that changes in extreme precipitation will actually be more extreme than previously estimated. Land use managers and planners should expect more extremes, but location matters."

The LOCA2 data set updates a similar analysis conducted in 2016 in advance of the Fourth National Climate Assessment (NCA), which was released in 2018 by the U.S. Global Change Research Program. The NCA is intended to assist the U.S. government with planning for, mitigating, and adapting to changes in climate that will affect the country. The Fifth NCA is expected to be issued later this year.

LOCA2 projections cover the lower 48 states of the United States, southern Canada, and northern Mexico. The data set draws on more than 70 years of weather data and incorporates 27 updated climate models from the Coupled Model Intercomparison Project (CMIP6), the latest iteration of an international effort to simulate climate that includes the "coupling" of natural systems such as the ocean and atmosphere to understand how they will act in concert as climate changes.

"We've spent a lot of effort improving the representation of extreme wet days, which is important for understanding both the likelihood of flooding and the availability of water for agricultural, commercial, and residential use," said David Pierce, a scientist at Scripps Oceanography and the developer of LOCA and LOCA2.

The LOCA2 climate projections are available through the end of the century down to the daily level, and for three different greenhouse gas emissions scenarios known as SSPs, or Shared Socioeconomic Pathways. The three scenarios are a medium level of emissions that is slightly less than current levels (SSP 245), medium-high (SSP 370), and high, where emissions greatly increase (SSP 585). The data set is freely available for planners and decision makers to use.

The projection reinforces what climate scientists have long predicted: Future weather events will become more extreme in a warming world. LOCA2 finds that the heaviest days of rain and snowfall across much of North America will likely release 20 to 30 percent more moisture than they do now. Much of the increased precipitation will occur in winter, potentially exacerbating flooding in regions such as the upper Midwest and the west coast.

"The big picture is clear: it's getting warmer and wetter," Feldman said. "This research translates that bigger picture into more practical data for infrastructure and operations planning. With this more detailed look at local impacts, we can help local officials make better-informed decisions, such as how long to make an airport runway, how much resilience to include for constructing buildings or bridges, or where to put crops or culverts."

The improved set of LOCA2 data was created by better identifying and preserving extreme weather events in the past, training models to more accurately reflect extremes in simulations of the future.

"We undertook a Herculean effort of personnel and computer time not just to produce a bunch of numbers, but to produce local projections that are relevant and useful," Feldman said. "We do so by recognizing how heat waves and storms have occurred and will occur at the local level, and projecting those forward."

Seasonal and regional predictions

While the data varies at the local level, researchers found substantial trends across the area covered by LOCA2 at the end of the century.

Across most seasons, a major part of North America will see roughly the same or fewer number of days with precipitation, roughly the same or fewer number of days with light and medium amounts of precipitation, and a large increase in the number of days with the most extreme precipitation (the top 1 percent and 0.1 percent of storms).

"People will be more affected by the really rare and most extreme events, because those are showing the biggest increase," said Pierce, who is the lead author of the paper on extreme precipitation published in the Journal of Hydrometeorology. "The wettest day you would expect to see in five years, or 50 years, or 500 years -- those extreme events are going to be substantially wetter, and that's a really big issue, because it has implications for flooding and run-off."

Southern Canada and most of the United States will see increases in extreme precipitation days that occur primarily in winter. The wettest days of precipitation will increase by 20-30 percent, depending on the emissions scenario and how extreme the storm is.

Arizona, New Mexico, and northern Mexico can expect increases in extreme precipitation days that occur primarily in autumn. The wettest days of precipitation increase by 10-30 percent, depending on which emissions scenarios come to be and how extreme the storms are. While the region becomes drier overall, the number of days with extreme precipitation events still goes up, meaning the precipitation that does come will often do so in larger storms.

"It's quite interesting that you see the same kind of pattern of fewer low- and medium- precipitation days and more extreme precipitation days across pretty much the entire country," Pierce said. Knowing the changing character of precipitation and the frequency of extreme events is useful in two ways, Pierce added. "One is for building new infrastructure in the future, and one is for understanding impacts upon existing facilities already there."

Read more at Science Daily

Shutting down nuclear power could increase air pollution

Nearly 20 percent of today's electricity in the United States comes from nuclear power. The U.S. has the largest nuclear fleet in the world, with 92 reactors scattered around the country. Many of these power plants have run for more than half a century and are approaching the end of their expected lifetimes.

Policymakers are debating whether to retire the aging reactors or reinforce their structures to continue producing nuclear energy, which many consider a low-carbon alternative to climate-warming coal, oil, and natural gas.

Now, MIT researchers say there's another factor to consider in weighing the future of nuclear power: air quality. In addition to being a low carbon-emitting source, nuclear power is relatively clean in terms of the air pollution it generates. Without nuclear power, how would the pattern of air pollution shift, and who would feel its effects?

The MIT team took on these questions in a new study appearing in Nature Energy. They lay out a scenario in which every nuclear power plant in the country has shut down, and consider how other sources such as coal, natural gas, and renewable energy would fill the resulting energy needs throughout an entire year.

Their analysis reveals that indeed, air pollution would increase, as coal, gas, and oil sources ramp up to compensate for nuclear power's absence. This in itself may not be surprising, but the team has put numbers to the prediction, estimating that the increase in air pollution would have serious health effects, resulting in an additional 5,200 pollution-related deaths over a single year.

If, however, more renewable energy sources become available to supply the energy grid, as they are expected to by the year 2030, air pollution would be curtailed, though not entirely. The team found that even under this heartier renewable scenario, there is still a slight increase in air pollution in some parts of the country, resulting in a total of 260 pollution-related deaths over one year.

When they looked at the populations directly affected by the increased pollution, they found that Black or African American communities -- a disproportionate number of whom live near fossil-fuel plants -- experienced the greatest exposure.

"This adds one more layer to the environmental health and social impacts equation when you're thinking about nuclear shutdowns, where the conversation often focuses on local risks due to accidents and mining or long-term climate impacts," says lead author Lyssa Freese, a graduate student in MIT's Department of Earth, Atmospheric and Planetary Sciences (EAPS).

"In the debate over keeping nuclear power plants open, air quality has not been a focus of that discussion," adds study author Noelle Selin, a professor in MIT's Institute for Data, Systems, and Society (IDSS) and EAPS. "What we found was that air pollution from fossil fuel plants is so damaging, that anything that increases it, such as a nuclear shutdown, is going to have substantial impacts, and for some people more than others."

The study's MIT-affiliated co-authors also include Principal Research Scientist Sebastian Eastham and Guillaume Chossière SM '17, PhD '20, along with Alan Jenn of the University of California at Davis.

Future phase-outs

When nuclear power plants have closed in the past, fossil fuel use increased in response. In 1985, the closure of reactors in Tennessee Valley prompted a spike in coal use, while the 2012 shutdown of a plant in California led to an increase in natural gas. In Germany, where nuclear power has almost completely been phased out, coal-fired power increased initially to fill the gap.

Noting these trends, the MIT team wondered how the U.S. energy grid would respond if nuclear power were completely phased out.

"We wanted to think about what future changes were expected in the energy grid," Freese says. "We knew that coal use was declining, and there was a lot of work already looking at the impact of what that would have on air quality. But no one had looked at air quality and nuclear power, which we also noticed was on the decline."

In the new study, the team used an energy grid dispatch model developed by Jenn to assess how the U.S. energy system would respond to a shutdown of nuclear power. The model simulates the production of every power plant in the country and runs continuously to estimate, hour by hour, the energy demands in 64 regions across the country.

Much like the way the actual energy market operates, the model chooses to turn a plant's production up or down based on cost: Plants producing the cheapest energy at any given time are given priority to supply the grid over more costly energy sources.

The team fed the model available data on each plant's changing emissions and energy costs throughout an entire year. They then ran the model under different scenarios, including: an energy grid with no nuclear power, a baseline grid similar to today's that includes nuclear power, and a grid with no nuclear power that also incorporates the additional renewable sources that are expected to be added by 2030.

They combined each simulation with an atmospheric chemistry model to simulate how each plant's various emissions travel around the country and to overlay these tracks onto maps of population density. For populations in the path of pollution, they calculated the risk of premature death based on their degree of exposure.

System response

Their analysis showed a clear pattern: Without nuclear power, air pollution worsened in general, mainly affecting regions in the East Coast, where nuclear power plants are mostly concentrated. Without those plants, the team observed an uptick in production from coal and gas plants, resulting in 5,200 pollution-related deaths across the country, compared to the baseline scenario.

They also calculated that more people are also likely to die prematurely due to climate impacts from the increase in carbon dioxide emissions, as the grid compensates for nuclear power's absence. The climate-related effects from this additional influx of carbon dioxide could lead to 160,000 additional deaths over the next century.

"We need to be thoughtful about how we're retiring nuclear power plants if we are trying to think about them as part of an energy system," Freese says. "Shutting down something that doesn't have direct emissions itself can still lead to increases in emissions, because the grid system will respond."

Read more at Science Daily

US forests face an unclear future with climate change

When you walk through a forest, you are surrounded by carbon. Every branch and every leaf, every inch of trunk and every tendril of unseen root contains carbon pulled from the atmosphere through photosynthesis. And as long as it stays stored away inside that forest, it's not contributing to the rising concentrations of carbon dioxide that cause climate change. So it's only natural that we might want to use forests' carbon-storage superpower as a potential climate solution in addition to reducing human greenhouse gas emissions.

But climate change itself might compromise how permanently forests are able to store carbon and keep it out of the air, according to a new study led by University of Utah researchers. A study of how different regions and tree species will respond to climate change finds a wide range of estimates of how much carbon forests in different regions might gain or lose as the climate warms. Importantly, the researchers found, the regions most at risk to lose forest carbon through fire, climate stress or insect damage are those regions where many forest carbon offset projects have been set up.

"This tells us there's a really urgent need to update these carbon offsets protocols and policies with the best available science of climate risks to U.S. forests," said William Anderegg, study senior author and director of the U's Wilkes Center for Climate Science and Policy.

The study is published in Nature Geoscience. Find an interactive tool showing carbon storage potential in forests in the U.S. here.

A multi-perspective modeling approach

For this study, the researchers were interested in forecasting changes in the amount of aboveground carbon storage in forests of different regions in the United States. Aboveground carbon refers to any living parts of a tree that are above ground, including wood and leaves or needles.

Scientists can look at the future of forests under climate change in a few different ways. They can look at historical and future projections of climate, or look at datasets from long-term forest plots. They can also use machine learning to identify which climate niches tree species most prefer. Or they can use complex models that include interactions between the ecosystem and the atmosphere.

Anderegg and colleagues, including first author and postdoctoral scholar Chao Wu, chose all of the above.

"Each different method has inherent advantages and limitations," Wu said. "No model is perfect."

"By bringing in many different approaches and different model types and comparing them," Anderegg said, "we can get a sense of what the different models are telling us and how can we learn to improve the models. And we might have much more confidence if all of the models and all of the approaches tell us the same story in a given region."

Analyzing the combined model outputs, the researchers found that although the models' forecasts differed in some ways, they did show some consistency in predictions of how different regions' carbon storage might change in the future. The Great Lakes and Northeastern US, for example, as well as parts of the Southeastern US and the northern Rockies, consistently showed carbon gains in future projections.

But the models also showed significant risks of losing carbon from forests through the climate triple threat of fire, climate stress and insect damage. With those risks, the models projected a net carbon gain in forests nationwide of between 3 and 5 petagrams of carbon by the end of the 21st century (a petagram is a quadrillion grams -- about 25 times the mass of all humans on Earth). Without those climate stresses, forests might be able to pack away a net 9.4 petagrams of carbon.

The researchers also applied their analysis to 139 current projects to offset carbon emissions to the atmosphere by aiming to increase the carbon stored in forests through various approaches.

"For carbon offsets to be effective," Anderegg said, "they have to store carbon for a pretty long amount of time -- multiple decades to centuries. So if fire's burning them down or insects are wiping out different areas, it could vastly undermine their effectiveness as climate change solutions."

Depending on the model method and the climate scenario, the researchers found that large numbers of carbon offset forest projects, particularly in the Southeastern US and on the West Coast, are projected to lose carbon by the end of the century.

What we still need to know

The results, Wu said, highlight that different climate and ecological models have different strengths and weaknesses, and considering them together reveals the areas of research needed to improve climate projections.

Tree demographic models, for example, include simulations of forest dynamics as old trees die and new trees grow. "But these current models didn't consider the disturbance-vegetation feedback," Wu said, referring to the different types of vegetation besides trees that appear following a disturbance like a forest fire and how they might influence the odds of another disturbance. "And also they didn't consider CO2 fertilization," or the potential for rising carbon dioxide levels to actually improve plant growth.

Anderegg identified three research questions that could help:
 

• How much rising CO2 concentrations might benefit plants and trees and help them grow more.
• Better data and understanding of climate-driven tree mortality from fire, climate stress, and insects.
• How biomes will shift around. Following a disturbance, for example, some forests may be able to grow back but some may transition to grasslands and be lost entirely.

"These are some of the biggest unknowns that the field is really racing to tackle," he said.

In the meantime, while science works to understand how climate change affects forests, society can help by slowing the pace of climate change.

Read more at Science Daily

A reconstruction of prehistoric temperatures for some of the oldest archaeological sites in North America

Scientists often look to the past for clues about how Earth's landscapes might shift under a changing climate, and for insight into the migrations of human communities through time. A new study offers both by providing, for the first time, a reconstruction of prehistoric temperatures for some of the first known North American settlements.

The study, published in Quaternary Science Reviews, uses new techniques to examine the past climate of Alaska's Tanana Valley. With a temperature record that reaches back 14,000 years, researchers now have a glimpse into the environment that supported humans living at some of the continent's oldest archaeological sites, where mammoth bones are preserved alongside evidence of human occupation. Reconstructing the past environment can help scientists understand the importance of the region for human migration into the Americas.

"When you think about what was happening in the Last Glacial Maximum, all these regions on Earth were super cold, with massive ice sheets, but this area was never fully glaciated," says Jennifer Kielhofer, Ph.D., a paleoclimatologist at DRI and lead author of the study. "We're hypothesizing that if this area was comparatively warm, maybe that would have been an attractive reason to come there and settle."

Kielhofer conducted the research during her doctoral studies at the University of Arizona, and was attracted to the Alaska location because of the wealth of research expertise being focused on the area. She also saw an opportunity to contribute to scientific understanding of a part of the world that is particularly sensitive to global climate change.

"We have to look to the past to try to better constrain how these areas have responded previously," she said, "and how they might respond in the future under climate scenarios that we predict."

Earlier research had relied on coarse temperature records by examining changes in vegetation and pollen. However, this information can only provide a general sense of whether a region was warming or cooling over time. To obtain a more precise history of temperatures, Kielhofer examined soil samples from the archeological sites. Using a technique known as brGDGT paleothermometry, she examined temperature records stored in bacteria to obtain a record of mean annual air temperature above freezing with a precision within about 2.8 degrees Celsius.

"Bacteria are everywhere," she said. "That's great because in areas where you might not have other means of recording or assessing past temperature, you have bacteria. They can preserve for millions of years, so it's a great opportunity to look at pretty much anywhere on Earth."

The results were surprising, she said, because many scientists had previously believed that the region experienced large swings in temperature, which may have contributed to the movement of early humans. But Kielhofer's data showed that temperatures in the Tanana Valley remained fairly stable over time.

"The region wasn't really responding to these global scale climate changes as we might expect," she said. "Because temperatures are really stable through this record, we can't necessarily use temperature as a way to explain changes in human occupation or adaptation through time, as scientists have previously tried to do."

Read more at Science Daily

New, exhaustive study probes hidden history of horses in the American West

A team of international researchers has dug into archaeological records, DNA evidence and Indigenous oral traditions to paint what might be the most exhaustive history of early horses in North America to date. The group's findings show that these beasts of burden may have spread throughout the American West much faster and earlier than many European accounts have suggested.

The researchers, including several scientists from the University of Colorado Boulder, published their findings today in the journal Science.

To tell the stories of horses in the West, the team closely examined about two dozen sets of animal remains found at sites ranging from New Mexico to Kansas and Idaho. The researchers come from 15 countries and multiple Native American groups, including the Lakota, Comanche and Pawnee nations.

"What unites everyone is the shared vision of telling a different kind of story about horses," said William Taylor, a corresponding author of the study and curator of archaeology at the CU Museum of Natural History. "Focusing only on the historical record has underestimated the antiquity and the complexity of Indigenous relationships with horses across a huge swath of the American West."

For many of the scientists involved, the research holds deep personal significance, added Taylor, who grew up in Montana where his grandfather was a rancher.

"We're looking at parts of the country that are extraordinarily important to the people on this project," he said.

The researchers drew on archaeozoology, radiocarbon dating, DNA sequencing and other tools to unearth how and when horses first arrived in various regions of today's United States. Based on the team's calculations, Indigenous communities were likely riding and raising horses as far north as Idaho and Wyoming by at least the first half of the 17th Century -- as much as a century before records from Europeans had suggested.

Groups like the Comanche, in other words, may have begun to form deep bonds with horses mere decades after the animals arrived in the Americas on Spanish boats.

The results line up with a wide range of Indigenous oral histories.

"All this information has come together to tell a bigger, broader, deeper story, a story that natives have always been aware of but has never been acknowledged," said Jimmy Arterberry, co-author of the new study and tribal historian of the Comanche Nation in Oklahoma.

Study co-author Carlton Shield Chief Gover agreed, noting that the love of horses may be one thing that extends across societies and borders.

"People are fascinated by horses. They've grown up with horses," said Shield Chief Gover, a citizen of the Pawnee Nation of Oklahoma and curator for public anthropology at the Indiana University Museum of Archaeology and Anthropology. "We can talk to one another through our shared love of an animal."

Mud Pony

For many Native American communities that shared love goes a long way back.

The Pawnee, for example, tell the story of "Mud Pony," a boy who began seeing visions of strange creatures in his sleep.

"He makes these little mud figurines of these animals he sees in his dreams, and, overnight, they become alive," Shield Chief Gover said. "That's how you get horses."

European historical records from the colonial period, however, have tended to favor a more recent origin story for horses in the West. Many scholars have suggested that Native American communities didn't begin caring for horses until after the Pueblo Revolt of 1680. During this event, Pueblo people in what is today New Mexico temporarily overthrew Spanish rule, releasing European livestock in the process.

Taylor, also an assistant professor of anthropology at CU Boulder, and his colleagues didn't think it fit as an origin story for the relationships between humans and horses in the West: "We thought: There's something fishy about this story."

Clues in bone

With funding from the U.S. National Science Foundation (NSF), they formed an equine dream team that includes archaeologists from the University of Oklahoma and University of New Mexico. Geneticist Ludovic Orlando and Lakota scholar Yvette Running Horse Collin took part from the University of Toulouse.

"This research demonstrates how multiple different types of data can be integrated to address the fascinating historical question of how and when horses spread across the West," said NSF Archaeology program director John Yellen.

The researchers began collecting as much data as they could on horses remains from the West. DNA evidence, for example, suggests that most Indigenous horses had descended from Spanish and Iberian horses, with British horses becoming more common in the 18th and 19th Centuries.

"Our analyses show it was born and raised locally," Taylor said. "It was cared for, and when that animal passed, there was extraordinary significance to that event."

The remains of this horse, along with several others from the study, also seemed to date back to around the turn of the 17th Century, decades before the start of the Pueblo Revolt.

How animals like it arrived in Wyoming isn't clear, but it's likely that Europeans weren't involved in their initial transport.

Shield Chief Gover explained that few Indigenous people will be surprised by the results of the study. But the team's findings may help to illustrate for academic scientists just how important these animals were to the history of Indigenous peoples. The Pawnee, who lived in Nebraska, for example, rode horses on twice-a-year buffalo hunts, traveling farther and faster into the "sea of grass" of the Great Plains. Comanche also galloped on horseback to hunt buffalo, while owning a lot of horses was a sign of wealth.

"I don't want to diminish the reverence and the respect we have for horses," Arterberry said. "We see them as gifts the Creator gave us, and, because of that, we survived and thrived and became who we are today."

Respecting horses

Study co-author Chance Ward, a master's student in Museum and Field Studies at CU Boulder, would like to see the archaeology community begin to treat those relationships with more respect. He was born and raised on the Cheyenne River Reservation in South Dakota, which is home to four bands of the Lakota Nation. Ward grew up listening to his mother's childhood stories about riding ponies in the Bear Creek community. His father's parents started a ranch on the reservation where members of the family practice rodeo today.

He explained that many researchers don't handle animal remains with the same care they reserve for cultural objects and human remains.

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Major North American oil source yields clues to one of earth's deadliest mass extinctions

The Bakken Shale Formation -- a 200,000-square-mile shale deposit below parts of Canada and North Dakota -- has supplied billions of barrels of oil and natural gas to North America for 70 years. A new discovery reveals that the rocks also open a uniquely informative window into Earth's complicated geological history.

A research team, which included geologists from the University of Maryland, George Mason University and the Norwegian oil and gas company Equinor, developed a new framework for analyzing paleontological and biogeochemical data extracted from the formation's rock. Using this technique, the team pinpointed a major trigger of several closely spaced biotic crises during the late Devonian Period almost 350 million years ago: euxinia, or the depletion of oxygen and expansion of hydrogen sulfide in large bodies of water. Published in the journal Nature on March 8, 2023, the team's findings demonstrate links between sea level, climate, ocean chemistry and biotic disruption.

"For the first time, we can point to a specific kill mechanism responsible for a series of significant biotic disruptions during the late Devonian Period," said UMD Geology Professor Alan Jay Kaufman, a senior author of the paper. "There have been other mass extinctions presumably caused by expansions of hydrogen sulfide before, but no one has ever studied the effects of this kill mechanism so thoroughly during such a critical period of Earth's history."

According to Kaufman, the late Devonian Period was a "perfect storm" of factors that played a large role in how Earth is today. Vascular plants and trees were especially crucial to the process; as they expanded on land, plants stabilized soil structure, helped spread nutrients to the ocean, and added oxygen and water vapor to the atmosphere while pulling carbon dioxide out of it.

"The introduction of terrestrial plants capable of photosynthesis and transpiration stimulated the hydrological cycle, which kick-started the Earth's capacity for more complex life as we know it today," Kaufman said.

The Devonian Period ended around the same time the Bakken sediments accumulated, allowing the layers of organic-rich shale to 'record' the environmental conditions that occurred there. Because the Earth's continents were flooded during that time, various sediments including black shale gradually accumulated in inland seas that formed within geological depressions like the Williston Basin, the preserved the Bakken formation.

Undergraduate laboratory assistant Tytrice Faison (B.S. '22, geology) -- who joined Kaufman's lab after taking a course with him through the Carillon Communities living-learning program -- prepared and analyzed more than 100 shale and carbonate samples taken from the formation. After analyzing the samples, Kaufman, Faison and the rest of the Bakken team deciphered clear layers of sediment representing three key biotic crises known as the Annulata, Dasberg and Hangenberg events, with the last crisis associated with one of the greatest mass extinctions in Earth history.

"We could see anoxic events distinctly marked by black shale and other geochemical deposits, which are likely linked to a series of rapid rises in sea level," Kaufman explained. "We suspect that sea levels may have risen during the pulsed events due to the melting ice sheets around the South Pole at this time."

Higher sea levels would have resulted in the flooding of interior continental margins, or the transitional region between oceanic and continental crusts. In these settings, high levels of nutrients, such as phosphorus and nitrogen, could have triggered algal blooms which create low oxygen zones in large bodies of water. These zones in turn would have increased toxic hydrogen sulfide right where most marine animals would have lived. Under those conditions, animals in the oceans and on land around the shoreline would have died during these late Devonian events.

The team's research is not exclusive to global biotic disruptions from hundreds of millions of years ago. Kaufman suggests that their findings are not just applicable to the shallow inland seas of the Devonian Period, but perhaps also to the oceans of today affected by global warming. He compared the ocean's circulatory system to a "conveyor belt" carrying nutrients, oxygen and microorganisms from place to place.

"Cold, salty water develops in the North Atlantic region before it sinks and eventually makes its way to the Indian and Pacific Oceans, cycling around the globe. This oceanic jet stream helps to spread life-sustaining oxygen through the oceans," Kaufman explained. "If that conveyor belt were to be slowed down due to global warming, parts of the ocean might be deprived of oxygen and potentially become euxinic."

The collateral damage caused by global warming might then promote animal migration out of dead zones or put Earth on a path to decreased diversity and increased rates of extinction, he added.

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Study into global daily air pollution shows almost nowhere on Earth is safe

In a world first study of daily ambient fine particulate matter (PM2.5) across the globe, a Monash University study has found that only 0.18% of the global land area and 0.001% of the global population are exposed to levels of PM2.5 - the world's leading environmental health risk factor - below levels of safety recommended by Word Health Organisation (WHO).

Importantly while daily levels have reduced in Europe and North America in the two decades to 2019, levels have increased Southern Asia, Australia, New Zealand, Latin America and the Caribbean, with more than 70% of days globally seeing levels above what is safe.

A lack of pollution monitoring stations globally for air pollution, has meant a lack of data on local, national, regional and global PM2.5 exposure. Now this study, led by Professor Yuming Guo, from the Monash University School of Public Health and Preventive Medicine, and published in the journal, Lancet Planetary Health, has provided a map of how PM2.5 has changed across the globe in the past decades.

The research team utilised traditional air quality monitoring observations, satellite-based meteorological and air pollution detectors, statistical and machine learning methods to more accurately assess PM2.5 concentrations globally, according to Professor Guo.

"In this study, we used an innovative machine learning approach to integrate multiple meteorological and geological information to estimate the global surface-level daily PM2.5 concentrations at a high spatial resolution of approximately 10km ×10km for global grid cells in 2000-2019, focusing on areas above 15 μg/m³ which is considered the safe limit by WHO (The threshold is still arguable)," he said.

The study reveals that annual PM2.5 concentration and high PM2.5 exposed days in Europe and northern America decreased over the two decades of the study -- whereas exposures increased in southern Asia, Australia and New Zealand, and Latin America and the Caribbean.

In addition, the study found that:

•     Despite a slight decrease in high PM2.5 exposed days globally, by 2019 more than 70% of days still had PM2.5 concentrations higher than 15 μg/m³.
•     In southern Asia and eastern Asia, more than 90% of days had daily PM2.5 concentrations higher than 15 μg/m³.
•     Australia and New Zealand had a marked increase in the number of days with high PM2.5 concentrations in 2019.
•     Globally, the annual average PM2.5 from 2000 to 2019 was 32.8 µg/m3.
•     The highest PM2.5 concentrations were distributed in the regions of Eastern Asia (50.0 µg/m3) and Southern Asia (37.2 µg/m3), followed by northern Africa (30.1 µg/m3).
•     Australia and New Zealand (8.5 μg/m³), other regions in Oceania (12.6 μg/m³), and southern America (15.6 μg/m³) had the lowest annual PM2.5 concentrations.
•     Based on the new 2021 WHO guideline limit, only 0.18% of the global land area and 0.001% of the global population were exposed to an annual exposure lower than this guideline limit (annual average of 5 μg/m³) in 2019.

According to Professor Guo, the unsafe PM2.5 concentrations also show different seasonal patterns "included Northeast China and North India during their winter months (December, January, and February), whereas eastern areas in northern America had high PM2.5 in its summer months (June, July, and August)," he said.

"We also recorded relatively high PM2.5 air pollution in August and September in South America and from June to September in sub-Saharan Africa."

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Global wetlands losses overestimated despite high losses in many regions

Sometime this spring or summer, the Supreme Court is expected to issue a case ruling that will legally define whether federal protections should be extended to wetlands outside of navigable waters. The justices might consider reading a new Stanford-led study that finds, although wetlands remain threatened in many parts of the world -- including the U.S., which accounts for more losses than any other country -- global losses of wetlands have likely been overestimated. Published Feb. 8 in Nature, the study's findings could help better explain the causes and impacts of wetland loss, enabling more informed plans to protect or restore ecosystems crucial for human health and livelihoods.

"Despite the good news that our results might imply, it remains urgent to halt and reverse the conversion and degradation of wetlands," said study lead author Etienne Fluet-Chouinard, a postdoctoral associate in Stanford's Department of Earth System Science at the time of the research. "The geographic disparities in losses are critical to consider because the forgone local benefits from drained wetlands cannot be replaced by wetlands elsewhere."

Rethinking wetlands

Now understood to be vital sources of water purification, groundwater recharge, and carbon storage, wetlands were long seen as unproductive areas teeming with disease-bearing insects and good only for draining to grow crops or harvest peat for fuel and fertilizer. Unrelenting drainage for conversion to human land uses, such as farmland and urban areas, in addition to alteration by fires and groundwater extraction, has made wetlands among the world's most threatened ecosystems in the world.

Accurately estimating the extent, distribution, and timing of wetland loss is key to understanding their role in natural processes and the impact of wetland drainage on the water and carbon cycles. A lack of historical data has hindered the effort, forcing scientists to make estimates based on incomplete collections of regional data on wetland loss.

"Wetlands purify our water, prevent flooding, and are biodiversity superheroes," said study co-author Rob Jackson, the Michelle and Kevin Douglas Provostial Professor of Energy and Environment in the Stanford Doerr School of Sustainability. "We need the best data possible to save what we have and know what we've lost."

A second chance

In a first-of-its-kind historical reconstruction, the researchers combed through thousands of records of wetland drainage and land-use changes in 154 countries, mapping the distribution of drained and converted wetlands onto maps of present-day wetlands to get a picture of what the original wetland area might have looked like in 1700.

They found that the area of wetland ecosystems has declined 21-35% since 1700 due to human intervention. That's far less than the 50-87% losses estimated by previous studies. Still, the authors estimate that at least 1.3 million square miles of wetlands have been lost globally -- an area about the size of Alaska, Texas, California, Montana, New Mexico, and Arizona combined.

"These new results allow us to better quantify changes in wetlands' sequestration of carbon from the atmosphere and emission of methane, another powerful greenhouse gas," said study co-author Avni Malhotra, a Stanford postdoctoral researcher at the time of the research.

The low estimate is likely the result of the study's focus beyond regions with historically high wetland losses, and its avoidance of large extrapolations -- characteristics of many previous estimates. The researchers note their estimate of losses is likely conservative because they constrained their analysis to available data, which is scarce for the years before 1850.

Despite what may seem to be good news, the researchers emphasize that wetland losses have been dramatically high in some regions, such as the U.S., which is estimated to have lost 40% of its wetlands since 1700 and accounts for more than 15% of all global losses during the study's time period. Although wetland conversion and degradation have slowed globally, it continues apace in some regions, such as Indonesia, where farmers and corporations continue to clear large swaths of land for oil palm plantations and other agricultural uses.

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