How does radiation travel through dense plasma?

Most people are familiar with solids, liquids, and gases as three states of matter. However, a fourth state of matter, called plasmas, is the most abundant form of matter in the universe, found throughout our solar system in the sun and other planetary bodies. Because dense plasma -- a hot soup of atoms with free-moving electrons and ions -- typically only forms under extreme pressure and temperatures, scientists are still working to comprehend the fundamentals of this state of matter. Understanding how atoms react under extreme pressure conditions -- a field known as high-energy-density physics (HEDP) -- gives scientists valuable insights into the fields of planetary science, astrophysics, and fusion energy.

One important question in the field of HEDP is how plasmas emit or absorb radiation. Current models depicting radiation transport in dense plasmas are heavily based on theory rather than experimental evidence.

n a new paper published in Nature Communications, researchers at the University of Rochester Laboratory for Laser Energetics (LLE) used LLE's OMEGA laser to study how radiation travels through dense plasma. The research, led by Suxing Hu, a distinguished scientist and group leader of the High-Energy-Density Physics Theory Group at the LLE and an associate professor of mechanical engineering, and Philip Nilson, a senior scientist in the LLE's Laser-Plasma Interaction group, provides first-of-its-kind experimental data about the behavior of atoms at extreme conditions. The data will be used to improve plasma models, which allow scientists to better understand the evolution of stars and may aid in the realization of controlled nuclear fusion as an alternative energy source.

"Experiments using laser-driven implosions on OMEGA have created extreme matter at pressures several billion times the atmospheric pressure at Earth's surface for us to probe how atoms and molecules behave at such extreme conditions," Hu says. "These conditions correspond to the conditions inside the so-called envelope of white dwarf stars as well as inertial fusion targets."

Using x-ray spectroscopy

The researchers used x-ray spectroscopy to measure how radiation is transported through plasmas. X-ray spectroscopy involves aiming a beam of radiation in the form of x-rays at a plasma made of atoms -- in this case, copper atoms -- under extreme pressure and heat. The researchers used the OMEGA laser both to create the plasma and to create the x-rays aimed at the plasma.

When the plasma is bombarded with x-rays, the electrons in the atoms "jump" from one energy level to another by either emitting or absorbing photons of light. A detector measures these changes, revealing the physical processes that are occurring inside the plasma, similar to taking an x-ray diagnostic of a broken bone.

A break from conventional theory

The researchers' experimental measurements indicate that, when radiation travels through a dense plasma, the changes in atomic energy levels do not follow conventional theories currently used in plasma physics models -- so-called "continuum-lowering" models. The researchers instead found that the measurements they observed in their experiments can only be explained using a self-consistent approach based on density-functional theory (DFT). DFT offers a quantum mechanical description of the bonds between atoms and molecules in complex systems. The DFT method was first described in the 1960s and was the subject of the 1998 Nobel Prize in Chemistry.

"This work reveals fundamental steps for rewriting current textbook descriptions of how radiation generation and transport occurs in dense plasmas," Hu says. "According to our experiments, using a self-consistent DFT approach more accurately describes the transport of radiation in a dense plasma." Says Nilson, "Our approach could provide a reliable way for simulating radiation generation and transport in dense plasmas encountered in stars and inertial fusion targets. The experimental scheme reported here, based on a laser-driven implosion, can be readily extended to a wide range of materials, opening the way for far-reaching investigations of extreme atomic physics at tremendous pressures."

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Researchers find genetic links between traits are often overstated

Many estimates of how strongly traits and diseases share genetic signals may be inflated, according to a new UCLA-led study that indicates current methods for assessing genetic relationships between traits fail to account for mating patterns.

Through the use of powerful genome sequencing technology, scientists in recent years have sought to understand the genetic associations between traits and disease risk, hoping that discoveries of shared genetics could point to clues for tackling diseases. However, UCLA researchers said their new study, published Nov. 17 in Science, provides caution against relying too heavily on genetic correlation estimates. They say that such estimates are confounded by non-biological factors more than has been previously appreciated.

Genetic correlation estimates typically assume that mating is random. But in the real world, partners tend to pair up because of many shared interests and social structures. As a result, some genetic correlations in previous work that have been attributed to shared biology may instead represent incorrect statistical assumptions. For example, previous estimates of genetic overlap between body mass index (BMI) and educational attainment are likely to reflect this type of population structure, induced by "cross-trait assortative mating," or how individuals of one trait tend to partner with individuals of another trait.

The study authors said genetic correlation estimates deserve more scrutiny, since these estimates been used to predict disease risk, glean for clues for potential therapies, inform diagnostic practices, and shape arguments about human behavior and societal issues. The authors said some in the scientific community have placed too much emphasis on genetic correlation estimates based on the idea that studying genes, because they are unalterable, can overcome confounding factors.

"If you just look at two traits that are elevated in a group of people, you can't conclude that they're there for the same reason," said lead author Richard Border, a postdoctoral researcher in statistical genetics at UCLA. "But there's been a kind of assumption that if you can track this back to genes, then you would have the causal story."

Based on their analysis of two large databases of spousal traits, researchers found that cross-trait assortative mating is strongly associated with genetic correlation estimates and plausibly accounts for a "substantial" portion of genetic correlation estimates.

"Cross-trait assortative mating has affected all of our genomes and caused interesting correlations between DNA you inherit from your mother and DNA you inherit from your father across the whole genome," said study co-author Noah Zaitlen, a professor of computational medicine and neurology at UCLA Health.

The researchers also examined genetic correlation estimates of psychiatric disorders, which have sparked debate in the psychiatric community because they appear to show genetic relationships among disorders that seemingly have little similarity, such as attention-deficit hyperactivity disorder and schizophrenia. The researchers found that genetic correlations for a number of unrelated traits could be plausibly attributed to cross-trait assortative mating and imperfect diagnostic practices. On the other hand, their analysis found stronger links for some pairs of traits, like anxiety disorders and major depression, suggesting that there truly is at least some shared biology.

"But even when there is a real signal there, we're still suggesting that we're overestimating the extent of that sharing," Border said.

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Black holes in eccentric orbit

When black holes collide in the universe, the clash shakes up space and time: the amount of energy released during the merger is so great that it causes space-time to oscillate, similar to waves on the surface of water. These gravitational waves spread out through the entire universe and can still be measured thousands of light years away, as was the case on 21 May 2019, when the two gravitational wave observatories LIGO (USA) and Virgo (Italy) captured such a signal. Named GW190521 after the date of its discovery, the gravitational wave event has since provoked discussion among experts because it differs markedly from previously measured signals.

The signal had initially been interpreted to mean that the collision involved two black holes moving in near-circular orbits around each other. "Such binary systems can be created by a number of astrophysical processes," explains Prof. Sebastiano Bernuzzi, a theoretical physicist from the University of Jena, Germany. Most of the black holes discovered by LIGO and Virgo, for example, are of stellar origin. "That means they are the remnants of massive stars in binary star systems," adds Bernuzzi, who led the current study. Such black holes orbit each other in quasi-circular orbits, just as the original stars did previously.

One black hole captures a second

"GW190521 behaves significantly differently, however," explains Rossella Gamba. The lead author of the publication is doing her doctorate in Jena Research Training Group 2522 and is part of Bernuzzi's team. "Its morphology and explosion-like structure are very different from previous observations." So, Rossella Gamba and her colleagues set out to find an alternative explanation for the unusual gravitational wave signal. Using a combination of state-of-the-art analytical methods and numerical simulations on supercomputers, they calculated different models for the cosmic collision. They came to the conclusion that it must have occurred on a strongly eccentric path instead of a quasi-circular one. A black hole initially moves freely in an environment that is relatively densely filled with matter and, as soon as it gets close to another black hole, it can be "captured" by the other's gravitational field. This also leads to the formation of a binary system, but here the two black holes do not orbit in a circle, but move eccentrically, in tumbling motions around each other.

"Such a scenario explains the observations much better than any other hypothesis presented so far. The probability is 1:4300," says Matteo Breschi, doctoral student and co-author of the study, who developed the infrastructure for the analysis. And postdoctoral researcher Dr Gregorio Carullo adds: "Even though we don't currently know exactly how common such dynamic movements by black holes are, we don't expect them to be a frequent occurrence." This makes the current results all the more exciting, he adds. Nevertheless, more research is needed to clarify beyond doubt the processes that created GW190521.

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Salt more important than cold polar temps in sea ice formation

When polar seas freeze and ice forms, it is not only due to cold air chilling the surface of the water. Even more important is that warm water is prevented from rising to the surface from the depths of the ocean, due to the much lower salinity of the surface water. Researchers from the University of Gothenburg and elsewhere have described this effect in a new scientific study.

Sea ice forms in the polar regions because it gets so cold in winter. However, cold water is heavier than warm water, so the chilled water should sink and not remain on the surface. This sinking should bring the warmer water back to the surface preventing ice to form in the oceans. Researchers from the University of Gothenburg and elsewhere are now presenting an explanation as to why it is not so. The study is presented in the journal Science Advances.

"The salinity of the surface water is lower, thanks to the supply of freshwater from melting ice at the poles and precipitation to the ocean. The difference in salinity between the surface water and the deeper water is an important factor for the formation of sea ice at low temperatures at the poles. Without the difference in salinity, the water would not have become stratified, leading to continuous mixing of sea water, thus preventing the formation of ice," says Fabien Roquet, professor of physical oceanography at the University of Gothenburg.

Difference in salinity creates a "lid"

The surface of the water, with its lower salinity, creates a "lid" that prevents warm water from rising to the surface. Without that lid, the cold polar temperatures would not be sufficient to freeze continuously moving warmer water.

The strength of this salinity lid is due to the unique properties of the seawater. In freshwater, water that is colder than 4 degrees Celsius has a lower density and therefore remains at the surface and freezes into ice, without mixing with water from greater depths. In the ocean, saltwater has a density that is lowest exactly at the freezing point, around -2C. However, the density of the water varies much less with the temperature in cold water than when it is warmer, which is very unusual for a fluid.

Sea ice inhibits the greenhouse effect

"The closer you get to the poles, the more important salinity is for limiting the mixing and evening out of water temperature throughout the water," says Fabien Roquet.

This discovery shows how important the special properties of the water molecule are for Earth's climate. The exchange of heat between the ocean and atmosphere is affected not only by temperature differences, but also by the salinity of the ocean. Without this fact, it would be impossible for sea ice to form to any greater extent. Sea ice is itself an important factor for impeding the greenhouse effect, because it reflects sunlight away.

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Planting trees can save lives, study shows

In the past 30 years, the non-profit organization Friends of Trees planted trees along the streets of Portland, Oregon. Now, a new study shows that each tree planted was associated with significant reductions in non-accidental and cardiovascular mortality (of 20% and 6%, respectively, for trees planted in the preceding 15-30 years). The researchers also estimate that the annual economic benefits of planting trees greatly exceed the cost of maintaining them. The study, co-led by the Barcelona Institute for Global Health (ISGlobal), an institution supported by the "la Caixa" Foundation, together with the USDA Forest Service, was published in Environment International.

Evidence pointing to an association between exposure to nature and lower mortality is accumulating. "However, most studies use satellite imaging to estimate the vegetation index, which does not distinguish different types of vegetation and cannot be directly translated into tangible interventions," says Payam Dadvand, ISGlobal researcher and senior author of the study.

Thus, the authors took advantage of a natural experiment that took place in the city of Portland: between 1990 and 2019, Friends of Trees planted 49,246 street trees (and kept records of where the trees were planted, and when). So, the research team looked at the number of trees planted in a given area (specifically, a census track, where approximately 4,000 people live) in the preceding 5, 10 or 15 years. They associated this information with mortality due to cardiovascular, respiratory or non-accidental causes in that same area, using data from the Oregon Health Authority.

The results show that in neighbourhoods in which more trees had been planted, mortality rates (deaths per 100,000 persons) were lower. This negative association was significant for cardiovascular and non-accidental mortality (that is, all causes excluding accidents), particularly for males and people over the age of 65.

Furthermore, the association got stronger as trees aged and grew: the reduction in mortality rate associated with trees planted 11-15 years before (30%) was double that observed with trees planted in the preceding 1-5 years (15%). This means that older trees are associated with larger decreases in mortality, and that preserving existing mature trees may be particularly important for public health.

This study doesn't provide a direct insight into how trees improve health. However, the finding that large trees have a greater health impact than smaller ones is telling, because larger trees are better at absorbing air pollution, moderating temperatures, and reducing noise (three factors linked to increased mortality).

"We observed the effect both in green and less green neighbourhoods, which suggests that street tree planting benefits both," says Geoffrey H. Donovan, from the USDA Forest Service and first author of the study. The analysis took into account other factors that may influence mortality, such as income, education and racial composition of the neighbourhoods.

Finally, according to the authors' estimates, the benefits of tree planting greatly outweigh the cost: the annual cost of planting and maintaining one urban tree in each of Portland's 140 census tract areas would range somewhere between 3,000 and 13,000 USD, while it would generate around 14.2 million USD annually in lives saved.

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Plant roots change shape and branch out for water

Researchers have discovered how plant roots adapt their shape to maximise their uptake of water, pausing branching when they lose contact with water and only resuming once they reconnect with moisture, ensuring they can survive even in the driest conditions.

Plant scientists from the University of Nottingham have discovered a novel water sensing mechanism that they have called 'Hydro-Signalling', which shows how hormone movement is linked with water fluxes. The findings have been published today in Science.

Water is the rate-limiting molecule for life on earth. The devastating impact of climate change is enhancing the effects of water stress on global agriculture. Climate change is causing rainfall patterns to become more erratic, impacting rain-fed crops in particular.

Roots play a critical role to reduce the impact of water stress on plants by adapting their shape (such as branching or growing deeper) to secure more water. Discovering how plant roots sense and adapt to water stress is vital importance for helping 'future proof' crops to enhance their climate resilience.

Using X-ray micro-CT imaging researchers were able to reveal that roots alter their shape in response to external moisture availability by linking the movement of water with plant hormone signals that control root branching.

The study provides critical information about the key genes and processes controlling root branching in response to limited water availability, helping scientists design novel approaches to manipulate root architecture to enhance water capture and yield in crops.

Dr. Poonam Mehra, postdoctoral fellow, from the School of Biosciences is one of the lead authors and explains: "When roots are in contact with moisture, a key hormone signal (auxin) moves inwards with water, triggering new root branches. However, when roots lose contact with moisture, they rely on internal water sources that mobilises another hormone signal (ABA) outwards, which acts to block the inwards movement of the branching signal. This simple, yet elegant mechanism enables plant roots to fine tune their shape to local conditions and optimize foraging."

Professor Malcolm Bennett, co-lead on the research adds: "Our plant research is vitally important for understanding how we can futureproof crops and find ways to ensure successful crop yields even in the most challenging climates. We are already experiencing a hotter climate and designing plants that can still access water in these conditions is vital and this research is an all important step in understanding how to do this." He continued: "These new discoveries were only possible because of the cutting-edge tools and collaborative approaches of the authors, which involved an international team of scientists based in the UK, Belgium, Sweden, USA and Israel.'"

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NASA's Webb catches fiery hourglass as new star forms

NASA's James Webb Space Telescope has revealed the once-hidden features of the protostar within the dark cloud L1527, providing insight into the beginnings of a new star. These blazing clouds within the Taurus star-forming region are only visible in infrared light, making it an ideal target for Webb's Near-Infrared Camera (NIRCam).

The protostar itself is hidden from view within the "neck" of this hourglass shape. An edge-on protoplanetary disk is seen as a dark line across the middle of the neck. Light from the protostar leaks above and below this disk, illuminating cavities within the surrounding gas and dust.

The region's most prevalent features, the clouds colored blue and orange in this representative-color infrared image, outline cavities created as material shoots away from the protostar and collides with surrounding matter. The colors themselves are due to layers of dust between Webb and the clouds. The blue areas are where the dust is thinnest. The thicker the layer of dust, the less blue light is able to escape, creating pockets of orange.

Webb also reveals filaments of molecular hydrogen that have been shocked as the protostar ejects material away from it. Shocks and turbulence inhibit the formation of new stars, which would otherwise form all throughout the cloud. As a result, the protostar dominates the space, taking much of the material for itself.

Despite the chaos that L1527 causes, it's only about 100,000 years old -- a relatively young body. Given its age and its brightness in far-infrared light as observed by missions like the Infrared Astronomical Satellite, L1527 is considered a class 0 protostar, the earliest stage of star formation. Protostars like these, which are still cocooned in a dark cloud of dust and gas, have a long way to go before they become full-fledged stars. L1527 doesn't generate its own energy through nuclear fusion of hydrogen yet, an essential characteristic of stars. Its shape, while mostly spherical, is also unstable, taking the form of a small, hot, and puffy clump of gas somewhere between 20 and 40% the mass of our Sun.

As the protostar continues to gather mass, its core gradually compresses and gets closer to stable nuclear fusion. The scene shown in this image reveals L1527 doing just that. The surrounding molecular cloud is made up of dense dust and gas being drawn to the center, where the protostar resides. As the material falls in, it spirals around the center. This creates a dense disk of material, known as an accretion disk, which feeds material to the protostar. As it gains more mass and compresses further, the temperature of its core will rise, eventually reaching the threshold for nuclear fusion to begin.

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NASA's Webb draws back curtain on universe's early galaxies

A few days after officially starting science operations, NASA's James Webb Space Telescope propelled astronomers into a realm of early galaxies, previously hidden beyond the grasp of all other telescopes until now.

"Everything we see is new. Webb is showing us that there's a very rich universe beyond what we imagined," said Tommaso Treu of the University of California at Los Angeles, principal investigator on one of the Webb programs. "Once again the universe has surprised us. These early galaxies are very unusual in many ways."

Two research papers, led by Marco Castellano of the National Institute for Astrophysics in Rome, Italy, and Rohan Naidu of the Harvard-Smithsonian Center for Astrophysics and the Massachusetts Institute of Technology in Cambridge, Massachusetts, have been published in the Astrophysical Journal Letters.

These initial findings are from a broader Webb research initiative involving two Early Release Science (ERS) programs: the Grism Lens-Amplified Survey from Space (GLASS), and the Cosmic Evolution Early Release Science Survey (CEERS).

With just four days of analysis, researchers found two exceptionally bright galaxies in the GLASS-JWST images. These galaxies existed approximately 450 and 350 million years after the big bang (with a redshift of approximately 10.5 and 12.5, respectively), though future spectroscopic measurements with Webb will help confirm.

"With Webb, we were amazed to find the most distant starlight that anyone had ever seen, just days after Webb released its first data," said Naidu of the more distant GLASS galaxy, referred to as GLASS-z12, which is believed to date back to 350 million years after big bang. The previous record holder is galaxy GN-z11, which existed 400 million years after the big bang (redshift 11.1), and was identified in 2016 by Hubble and Keck Observatory in deep-sky programs.

"Based on all the predictions, we thought we had to search a much bigger volume of space to find such galaxies," said Castellano.

"These observations just make your head explode. This is a whole new chapter in astronomy. It's like an archaeological dig, and suddenly you find a lost city or something you didn't know about. It's just staggering," added Paola Santini, fourth author of the Castellano et al. GLASS-JWST paper.

"While the distances of these early sources still need to be confirmed with spectroscopy, their extreme brightnesses are a real puzzle, challenging our understanding of galaxy formation," noted Pascal Oesch at the University of Geneva in Switzerland, second author of the Naidu et al. paper.

The Webb observations nudge astronomers toward a consensus that an unusual number of galaxies in the early universe were much brighter than expected. This will make it easier for Webb to find even more early galaxies in subsequent deep sky surveys, say researchers.

"We've nailed something that is incredibly fascinating. These galaxies would have had to have started coming together maybe just 100 million years after the big bang. Nobody expected that the dark ages would have ended so early," said Garth Illingworth of the University of California at Santa Cruz, a member of the Naidu/Oesch team. "The primal universe would have been just one hundredth its current age. It's a sliver of time in the 13.8 billion-year-old evolving cosmos."

Erica Nelson of the University of Colorado, a member of the Naidu/Oesch team, noted that "our team was struck by being able to measure the shapes of these first galaxies; their calm, orderly disks question our understanding of how the first galaxies formed in the crowded, chaotic early universe." This remarkable discovery of compact disks at such early times was only possible because of Webb's much sharper images, in infrared light, compared to Hubble.

"These galaxies are very different than the Milky Way or other big galaxies we see around us today," said Treu.

Illingworth emphasized the two bright galaxies found by these teams have a lot of light. He said one option is that they could have been very massive, with lots of low-mass stars, like later galaxies. Alternatively, they could be much less massive, consisting of far fewer extraordinarily bright stars, known as Population III stars. Long theorized, they would be the first stars ever born, blazing at blistering temperatures and made up only of primordial hydrogen and helium -- before stars could later cook up heavier elements in their nuclear fusion furnaces. No such extremely hot, primordial stars are seen in the local universe.

"Indeed, the farthest source is very compact, and its colors seem to indicate that its stellar population is particularly devoid of heavy elements and could even contain some Population III stars. Only Webb spectra will tell," said Adriano Fontana, second author of the Castellano et al. paper and a member of the GLASS-JWST team.

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Tiniest ever ancient seawater pockets revealed

Trapped for millennia, the tiniest liquid remnants of an ancient inland sea have now been revealed. The surprising discovery of seawater sealed in what is now North America for 390 million years opens up a new avenue for understanding how oceans change and adapt with the changing climate. The method may also be useful in understanding how hydrogen can be safely stored underground and transported for use as a carbon-free fuel source.

"We discovered we can actually dig out information from these mineral features that could help inform geologic studies, such as the seawater chemistry from ancient times," said Sandra Taylor, first author of the study and a scientist at the Department of Energy's Pacific Northwest National Laboratory.

Taylor worked with PNNL colleagues Daniel Perea, John Cliff, and Libor Kovarik to perform the analyses in collaboration with geochemists Daniel Gregory of the University of Toronto and Timothy Lyons of the University of California, Riverside. The research team reported their discovery in the December 2022 issue of Earth and Planetary Science Letters.

Ancient seas; modern tools

Many types of minerals and gems contain small pockets of trapped liquid. Indeed, some gemstones are prized for their light-catching bubbles of liquid trapped within. What's different in this study is that scientists were able to reveal what was inside the tiniest water pockets, using advanced microscopy and chemical analyses.

The findings of the study confirmed that the water trapped inside the rock fit the chemistry profile of the ancient inland saltwater sea that once occupied upstate New York, where the rock originated. During the Middle Devonian period, this inland sea stretched from present day Michigan to Ontario, Canada. It harbored a coral reef to rival Australia's Great Barrier Reef. Sea scorpions the size of a pickup truck patrolled waters that harbored now-extinct creatures like trilobites, and the earliest examples of horseshoe crabs.

But eventually the climate changed, and along with that change, most of the creatures and the sea itself disappeared, leaving behind only fossil remains embedded in sediments that eventually became the pyrite rock sample used in the current experiment.

Clues to an ancient climate and to climate change

Scientists use rock samples as evidence to piece together how the climate has changed over the long span of geologic time.

"We use mineral deposits to estimate the temperature of the ancient oceans," said Gregory, a geologist at the University of Toronto, and one of the study leaders. But there are relatively few useful examples in the geological record.

"Salt deposits from trapped seawater [halite] are relatively rare in the rock record, so there are millions of years missing in the records and what we currently know is based on a few localities where there is halite found," Gregory said. By contrast, pyrite is found everywhere. "Sampling with this technique could open up millions of years of the geologic record and lead to new understanding of changing climate."

Seawater surprise

The research team was trying to understand another environmental issue -- toxic arsenic leaching from rock -- when they noticed the tiny defects. Scientists describe the appearance of these particular pyrite minerals as framboids -- derived from the French word for raspberry -- because they look like clusters of raspberry segments under the microscope.

"We looked at these samples through the electron microscope first, and we saw these kind of mini bubbles or mini features within the framboid and wondered what they were," Taylor said.

Using the precise and sensitive detection techniques of atom probe tomography and mass spectrometry -- which can detect minuscule amounts of elements or impurities in minerals -- the team worked out that the bubbles indeed contained water and their salt chemistry matched that of ancient seas.

From ancient sea to modern energy storage

These types of studies also have the potential to provide interesting insights into how to safely store hydrogen or other gases underground.

"Hydrogen is being explored as a low-carbon fuel source for various energy applications. This requires being able to safely retrieve and store large-amounts of hydrogen in underground geologic reservoirs. So it's important to understand how hydrogen interacts with rocks," said Taylor. "Atom probe tomography is one of the few techniques where you can not only measure atoms of hydrogen, but you can actually see where it goes in the mineral. This study suggests that tiny defects in minerals might be potential traps for hydrogen. So by using this technique we could figure out what's going on at the atomic level, which would then help in evaluating and optimizing strategies for hydrogen storage in the subsurface."

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Welsh 'weird wonder' fossils add piece to puzzle of arthropod evolution

The most famous fossils from the Cambrian explosion of animal life over half a billion years ago are very unlike their modern counterparts. These "weird wonders," such as the five-eyed Opabinia with its distinctive frontal proboscis, and the fearsome apex predator Anomalocaris with its radial mouthparts and spiny feeding appendages, have become icons in popular culture. However, they were only quite recently recognised as extinct stages of evolution that are crucial for understanding the origins of one of the largest and most important animal phyla, the arthropods (a group that includes modern crabs, spiders, and millipedes).

In an article published today in Nature Communications, two new specimens with striking similarities to Opabinia are described from a new fossil deposit recording life in the Ordovician Period, 40 million years after the Cambrian explosion. This deposit, located in a sheep field near Llandrindod Wells in mid Wales (UK), was discovered during the COVID-19 lockdowns by independent researchers and Llandrindod residents Dr Joseph Botting and Dr Lucy Muir, Honorary Research Fellows at Amgueddfa Cymru -- National Museum Wales.

The quarry is well known as one of several local sites yielding new species of fossil sponges. "When the lockdown started, I thought I'd make one more trip to collect some last sponges before finally writing them up," said Botting, "of course, that was the day that I found something sticking its tentacles out of a tube instead."

"This is the sort of thing that palaeontologists dream of, truly soft-body preservation," said Muir, "we didn't sleep well, that night." That was the beginning of an extensive and ongoing investigation that grew into an international collaboration, with lead author Dr Stephen Pates (University of Cambridge) and senior author Dr Joanna Wolfe (The Department of Organismic and Evolutionary Biology at Harvard University).

Among the fossils unearthed so far are two very unexpected leftovers from the Cambrian "weird wonders." Pates met with Botting and Muir to study the specimens using microscopes purchased through crowd-funding to examine the tiny specimens. The larger specimen measured 13 mm, while the smaller measured a miniscule 3 mm (for comparison Opabinia specimens can be 20 times as long).

Exhaustive studies during this visit revealed additional details in the new specimens. Some of these features are also found in Opabinia, such as triangular, squishy lobopod 'legs' for interacting with the sediment, and -- in the smaller specimen -- a tail fan with blades similar in shape to Opabinia's recently described sister, Utaurora. However other features recognised in the material, such as sclerites covering the head as well as the presence of spines on the proboscis, were not known from any opabiniid and instead hinted at possible radiodont (including Anomalocaris) affinities. The differences between the two specimens led the researchers to wonder were these due to changes during the growth of one species, or did they instead suggest that two distinct species were present in this new deposit?

The authors describe the new taxon, Mieridduryn bonniae, with the larger specimen designated the holotype. The status of the smaller specimen was left open, reflecting these different possibilities. "The size of the smaller specimen is comparable to some modern arthropod larvae -- we had to take into account this possibility in our analyses," said Wolfe.

The genus name Mieridduryn is derived from the Welsh language, and translates as "bramble-snout," reflecting the spiny proboscis in the new material. It is pronounced like "me-airy-theerin." "Many scientific names are made using Latin or Greek words," Muir said, "but we really wanted to honour Wales, where the specimens were discovered, and so chose to use the Welsh language." The species name bonniae pays tribute to the niece of the landowners, Bonnie. "The landowners have been very supportive of our research, and Bonnie has been avidly following our progress, even attending some of our Zoom updates," said Botting.

The researchers used phylogenetic analyses, comparing the new fossils with 57 other living and fossil arthropods, radiodonts, and panarthropods, to determine their place in the history of arthropod evolution. "The best-supported position for our Welsh specimens, whether considered as one or two species, were more closely related to modern arthropods than to opabiniids. These analyses suggested that Mieridduryn and the smaller specimen were not "true" opabiniids," said Pates.

Crucially, these results suggested that a proboscis -- thought to represent a fused pair of head appendages -- was not unique to opabiniids, but instead was present in the common ancestor of radiodonts and deuteropods (more derived, modern arthropods), and through evolutionary time may have reduced to become the labrum that covers the mouth in modern arthropods. However, the second-best-supported position for these specimens was as true opabiniids, so the authors enquired a bit further to test the robustness of this first result.

"These Welsh animals are 40 million years younger than Opabinia and Utaurora" said Wolfe, "so it was important to assess the implications of some features, such as spines on the appendages or a carapace, evolving convergently with radiodonts in our analyses." If some, or all, the features shared between the Welsh animals and radiodonts were instead considered to have evolved convergently, the analyses strongly favoured these specimens being considered true opabiniids, the first from outside North America and the youngest by 40 million years. Whatever the eventual conclusion, the fossils are an important new piece in the arthropod evolutionary jigsaw.

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Exploring the possibility of extraterrestrial life living in caves

Is there life in Martian caves?

It's a good question, but it's not the right question -- yet. An international collaboration of scientists led by NAU researcher Jut Wynne has dozens of questions we need asked and answered. Once we figure out how to study caves on the Moon, Mars and other planetary bodies, then we can return to that question.

Wynne, an assistant research professor of cave ecology, is the lead author of two related studies, both published in a special collection of papers on planetary caves by the Journal of Geophysical Research Planets. The first, "Fundamental Science and Engineering Questions in Planetary Cave Research," was done by an interdisciplinary team of 31 scientists, engineers and astronauts who produced a list of 198 questions that they, working with another 82 space and cave scientists and engineers, narrowed down to the 53 most important. Harnessing the knowledge of a considerable swath of the space science community, this work is the first study designed to identify the research and engineering priorities to advance the study of planetary caves. The team hopes their work will inform what will ultimately be needed to support robotic and human missions to a planetary cave -- namely on the Moon and/or Mars.

The second, "Planetary Caves: A Solar System View of Products and Processes," was born from the first study. Wynne realized there had been no effort to catalog planetary caves across the solar system, which is another important piece of the big-picture puzzle. He assembled another team of planetary scientists to tackle that question.

"With the necessary financial investment and institutional support, the research and technological development required to achieve these necessary advancements over the next decade are attainable," Wynne said. "We now have what I hope will become two foundational papers that will help propel planetary cave research from an armchair contemplative exercise to robots probing planetary subsurfaces."

What we know about extraterrestrial caves

There are a lot of them. Scientists have identified at least 3,545 potential caves on 11 different moons and planets throughout the solar system, including the Moon, Mars and moons of Jupiter and Saturn. Cave formation processes have even been identified on comets and asteroids. If the surrounding environment allows for access into the subsurface, that presents an opportunity for scientific discovery that's never been available before.

The discoveries in these caves could be massive. Caves may one day allow scientists to "peer into the depths" of these rocky and icy bodies, which will provide insights into how they were formed (but also can provide further insights into how Earth was formed). They could also, of course, hold secrets of life.

"Caves on many planetary surfaces represent one of the best environments to search for evidence of extinct or perhaps extant lifeforms," Wynne said. "For example, as Martian caves are sheltered from deadly surface radiation and violent windstorms, they are more likely to exhibit a more constant temperature regime compared to the surface, and some may even contain water ice. This makes caves on Mars one of the most important exploration targets in the search for life."

And it's not just finding life -- these same factors make caves good locations for astronaut shelters on Mars and the Moon when crewed missions are able to explore.

"Radiation shielding will be essential for human exploration of the Moon and Mars," said Leroy Chiao, a retired astronaut, former commander of the International Space Station and co-author of the first paper. "One possible solution is to utilize caves for this purpose. The requirements for astronaut habitats, EVA suits and equipment should take cave exploration and development into consideration, for protection from both solar and galactic cosmic radiation."

What Earth can tell us about other planets

Wynne, whose primary research is in terrestrial caves, said planetary cave research has long been a parallel research question to the earthly variety for nearly two decades. Caves support unique ecosystems that are sometimes quite divorced from the surface ecosystem in the same area. Who's to say a cave on the Moon or Mars would not be similar? So, many questions he's investigated about caves on Earth, he's wondered how it could apply on other planets.

He's not the only one making the connection. Wynne has done multiple research projects with NASA to help advance detection technologies, and his modeling of cave habitats does not much care if a cave is terrestrial or extraterrestrial. There are enough similarities in the cave environment to make reasonable predictions that will factor prominently into the selection of cave targets for exploration.

"Tellurian caves at depth are often characterized by complete darkness, a stable temperature approximating the average annual surface temperature, low to no air flow and a near-water-saturated atmosphere," he said. "The caves of other planetary bodies likely exhibit similar environmental conditions, but these will also be influenced by the surface conditions of the planetary body and the internal structure of the cave."

Keith Cowing, editor of SpaceRef.com and NASAWatch.com, said using the existing infrastructure of a planet's surface and subsurface may help humans get to other planets sooner than if we had to bring everything needed to survive with us.

"Humans have been living in caves for hundreds of thousands of years. Then they built their own when none were available," he said. "As such, it is only natural to assume that caves will offer similar utility as humanity expands to other worlds. While planet-wide terraforming may be an end goal, the use of large, pre-existing structures such as caves and lava tubes may be a more practical way to bootstrap the technology to the maturity needed to tackle the surface of an entire planet."

Where are we now?

While much of this research is forward-looking, there's also a need to consider what resources, research and support currently exist. Numerous robotic platforms and instrumentation suites are being tested, but the roadblock comes where it so often does -- the lack of funding. With sufficient support, a robotic exploration mission to a lunar or Martian cave could be possible in the next five to 10 years.

This research builds on past work to form a road map of sorts to move forward; Wynne sees it as a to-do list for that same process. The questions the scientists and engineers answered identify the tasks needed to prepare for that robotic exploration; it also looks even further ahead to the advancements needed in spacesuit technology, habitation modules and hardware that will enable humans to live and work safely underground on the Moon and Mars.

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Corporal punishment affects brain activity, anxiety, and depression

Don't spank your kids. That's the conventional wisdom that has emerged from decades of research linking corporal punishment to a decline in adolescent health and negative effects on behavior, including an increased risk for anxiety and depression. Now, a new study explores how corporal punishment might impact neural systems to produce those adverse effects.

Corporal punishment can be simply defined as the "intentional infliction of physical pain by any means for the purpose of punishment, correction, discipline, instruction, or any other reason." This violence, particularly when inflicted by a parent, evokes a complex emotional experience. The researchers, led by Kreshnik Burani, MS, and working with Greg Hajcak, PhD, at Florida State University, wanted to understand the neural underpinnings of that experience and its downstream consequences.

The study appears in Biological Psychiatry: Cognitive Neuroscience and Neuroimaging, published by Elsevier.

The researchers conducted a longitudinal study on 149 boys and girls ages 11 to 14 from the Tallahassee, FL, area. Participants performed a video game-like task and a monetary guessing game while undergoing continuously recorded electroencephalography, or EEG -- a noninvasive technique to measure brain-wave activity from the scalp. From the EEG data, the researchers determined two scores for each participant -- one reflecting their neural response to error and the other reflecting their neural response to reward.

Two years later, participants and their parents completed a series of questionnaires to screen for anxiety and depression and to assess parenting style. As expected, kids who had experienced corporal punishment were more likely to develop anxiety and depression.

"Our paper first replicates the well-known negative effect that corporal punishment has on a child's wellbeing: we found that corporal punishment is associated with increased anxiety and depressive symptoms in adolescence. However, our study goes further to demonstrate that corporal punishment might impact brain activity and neurodevelopment," said Burani.

That was reflected by larger neural response to error and a blunted response to reward in the adolescents who received physical punishments.

"Specifically," Burani added, "our paper links corporal punishment to increased neural sensitivity to making errors and decreased neural sensitivity to receiving rewards in adolescence. In previous and ongoing work with Dr. Hajcak, we see that increased neural response to errors is associated with anxiety and risk for anxiety, whereas decreased neural response to rewards is related to depression and risk for depression. Corporal punishment, therefore, might alter specific neurodevelopmental pathways that increase risk for anxiety and depression by making children hypersensitive to their own mistakes and less reactive to rewards and other positive events in their environment."

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Footprints claimed as evidence of ice age humans in North America need better dating, new research shows

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

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

"I read the original Science article on the human footprints at White Sands and was initially struck not only by how tremendous the footprints were on their own, but how important accurate dating would be," says Charles Oviatt, emeritus professor of geology at Kansas State University and one of the new study's authors. "I saw potential problems with the scientific tests of the dates reported in the Science paper."

"It really does throw a lot of what we think we know into question," says David Rhode, Ph.D., a paleoecologist at DRI and co-author of the new study. "That's why it's important to really nail down this age, and why we're suggesting that we need better evidence."

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

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

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

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

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

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

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

The dating of the footprints can be resolved through other methods, including radiocarbon dating of terrestrial plants (which use atmospheric carbon and not carbon from groundwater) and optically stimulated luminescence dating of quartz found in the sediment, the authors write.

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Wireless earphones work as inexpensive hearing aids

Some commercial earbuds can perform as well as hearing aids. The result, presented November 15 in the journal iScience, could help a large proportion of people with hearing loss access more affordable sound amplification devices.

Hearing loss has broad health impacts, but professional hearing aids are expensive and require multiple visits to otolaryngologists and audiologists for tuning. These factors lead to major barriers for many to access professional hearing aids. One estimate suggests nearly 75% of people with hearing loss in the United States do not use hearing aids.

"There's also a social stigma associated with hearing aids," says Yen-fu Cheng, the study's corresponding author and an otolaryngologist at Taipei Veterans General Hospital. "Many patients are reluctant to wear them because they don't want to appear old. So, we started exploring if there're are more accessible alternatives."

Apple came out with a feature called "Live Listen" in 2016 that allows people to use its wireless earphones, AirPods, and iPhone for sound amplification. The feature makes AirPods functionally similar to a personal sound amplification product, which is designed for people with normal hearing for certain occasions like birdwatching.

Cheng and his team wanted to investigate whether AirPods, which are widely available devices, can serve as alternative hearing aids. The team compared Airpods 2 and AirPods Pro -- the model with a noise canceling feature -- with a type of premium hearing aids and a basic pair of hearing aids. The premium hearing aids cost $10,000, and the basic type cost $1,500. Both models of AirPods are significantly cheaper than hearing aids, with AirPods 2 costing $129 and AirPods Pro costing $249. Notably, AirPods Pro met four out of five technology standards for hearing aids.

The team tested the four devices with 21 participants with mild to moderate hearing loss. The researchers read a short sentence, such as "the electricity bills went up recently," to participants, who were asked to repeat their words verbatim wearing the devices. They found AirPods Pro performed similarly well compared with basic hearing aids in a quiet environment and is slightly inferior to premium hearing aids. AirPods 2, while having the lowest performance among the four, helped participants hear more clearly compared with wearing no hearing aids.

In a noisy environment, AirPods Pro showed comparable performance to premium hearing aids when the noises came from the lateral direction of the participant. But when the noises came from the front of the participants, both AirPods models failed to help participants hear better.

"Two reasons may account for the difference between the two scenarios," says Ying-Hui Lai, the study's co-author and a bioengineer at National Yang Ming Chiao Tung University in Taipei. "It may relate to the trajectories soundwaves travel with, as well as the advanced signal processing algorithm by premium hearing aids. This finding will hopefully inspire engineers to design hearing aids and personal sound amplification products that are more sensitive in certain directions." He adds that AirPods Pro appears to perform better than AirPods 2, likely because of its noise-canceling feature.

"Globally, the wireless earphone market is growing rapidly. Some companies are interested in exploring the possibility of designing earbuds with sound amplification features. Our study proves that the idea is plausible," Lai says.

As a clinician, Cheng says persuading patients to use hearing aids is often challenging. "These wireless earbuds are of course not perfect, but they would be a good starting point for many patients who don't have access to professional hearing aids. They will see an increase in quality of life even with these earbuds." Cheng says.

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Cosmic chocolate pralines: General neutron star structure revealed

So far, little is known about the interior of neutron stars, those extremely compact objects that can form after the death of a star: the mass of our sun or even more is compressed into a sphere with the diameter of a large city. Since their discovery more than 60 years ago, scientists have been trying to decipher their structure. The greatest challenge is to simulate the extreme conditions inside neutron stars, as they can hardly be recreated on Earth in the laboratory. There are therefore many models in which various properties -- from density and temperature -- are described with the help of so-called equations of state. These equations attempt to describe the structure of neutron stars from the stellar surface to the inner core.

Now physicists at Goethe University Frankfurt have succeeded in adding further crucial pieces to the puzzle. The working group led by Prof. Luciano Rezzolla at the Institute of Theoretical Physics developed more than a million different equations of state that satisfy the constraints set by data obtained from theoretical nuclear physics on the one hand, and by astronomical observations on the other. When evaluating the equations of state, the working group made a surprising discovery: "Light" neutron stars (with masses smaller than about 1.7 solar masses) seem to have a soft mantle and a stiff core, whereas "heavy" neutron stars (with masses larger than 1.7 solar masses) instead have a stiff mantle and a soft core. "This result is very interesting because it gives us a direct measure of how compressible the centre of neutron stars can be," says Prof. Luciano Rezzolla, "Neutron stars apparently behave a bit like chocolate pralines: light stars resemble those chocolates that have a hazelnut in their centre surrounded by soft chocolate, whereas heavy stars can be considered more like those chocolates where a hard layer contains a soft filling."

Crucial to this insight was the speed of sound, a study focus of Bachelor's student Sinan Altiparmak. This quantity measure describes how fast sound waves propagate within an object and depends on how stiff or soft matter is. Here on Earth, the speed of sound is used to explore the interior of the planet and discover oil deposits.

By modelling the equations of state, the physicists were also able to uncover other previously unexplained properties of neutron stars. For example, regardless of their mass, they very probably have a radius of only 12 km. Thus, they are just as large in diameter as Goethe University's hometown Frankfurt. Author Dr. Christian Ecker explains: "Our extensive numerical study not only allows us to make predictions for the radii and maximum masses of neutron stars, but also to set new limits on their deformability in binary systems, that is, how strongly they distort each other through their gravitational fields. These insights will become particularly important to pinpoint the unknown equation of state with future astronomical observations and detections of gravitational waves from merging stars."

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Honey bee life spans are 50% shorter today than they were 50 years ago

A new study by University of Maryland entomologists shows that the lifespan for individual honey bees kept in a controlled, laboratory environment is 50% shorter than it was in the 1970s. When scientists modeled the effect of today's shorter lifespans, the results corresponded with the increased colony loss and reduced honey production trends seen by U.S. beekeepers in recent decades.

Colony turnover is an accepted factor in the beekeeping business, as bee colonies naturally age and die off. But over the past decade, U.S. beekeepers have reported high loss rates, which has meant having to replace more colonies to keep operations viable. In an effort to understand why, researchers have focused on environmental stressors, diseases, parasites, pesticide exposure and nutrition.

This is the first study to show an overall decline in honey bee lifespan potentially independent of environmental stressors, hinting that genetics may be influencing the broader trends seen in the beekeeping industry. The study was published November 14, 2022, in the journal Scientific Reports.

"We're isolating bees from the colony life just before they emerge as adults, so whatever is reducing their lifespan is happening before that point," said Anthony Nearman, a Ph.D. student in the Department of Entomology and lead author of the study. "This introduces the idea of a genetic component. If this hypothesis is right, it also points to a possible solution. If we can isolate some genetic factors, then maybe we can breed for longer-lived honey bees."

Nearman first noticed the decline in lifespan while conducting a study with entomology associate professor Dennis van Engelsdorp on standardized protocols for rearing adult bees in the laboratory. Replicating earlier studies, the researchers collected bee pupae from honey bee hives when the pupae were within 24 hours of emerging from the wax cells they are reared in. The collected bees finished growing in an incubator and were then kept as adults in special cages.

Nearman was evaluating the effect of supplementing the caged bees' sugar water diet with plain water to better mimic natural conditions when he noticed that, regardless of diet, the median lifespan of his caged bees was half that of caged bees in similar experiments in the 1970s. (17.7 days today versus 34.3 days in the 1970s.) This prompted a deeper review of published laboratory studies over the past 50 years.

"When I plotted the lifespans over time, I realized, wow, there's actually this huge time effect going on," Nearman said. "Standardized protocols for rearing honey bees in the lab weren't really formalized until the 2000s, so you would think that lifespans would be longer or unchanged, because we're getting better at this, right? Instead, we saw a doubling of mortality rate."

Although a laboratory environment is very different from a colony, historical records of lab-kept bees suggest a similar lifespan to colony bees, and scientists generally assume that isolated factors that reduce lifespan in one environment will also reduce it in another. Previous studies had also shown that in the real world, shorter honey bee lifespans corresponded to less foraging time and lower honey production. This is the first study to connect those factors to colony turnover rates.

When the team modeled the effect of a 50% reduction in lifespan on a beekeeping operation, where lost colonies are replaced annually, the resulting loss rates were around 33%. This is very similar to the average overwinter and annual loss rates of 30% and 40% reported by beekeepers over the past 14 years.

Nearman and vanEngelsdorp noted that their lab-kept bees could be experiencing some sort of low-level viral contamination or pesticide exposure during their larval stage, when they're brooding in the hive and worker bees are feeding them. But the bees have not shown overt symptoms of those exposures and a genetic component to longevity has been shown in other insects such as fruit flies.

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Oldest evidence of the controlled use of fire to cook food, researchers report

A remarkable scientific discovery has been made by researchers from the Hebrew University of Jerusalem (HU), Tel Aviv University (TAU), and Bar-Ilan University (BIU), in collaboration with the Steinhardt Museum of Natural History, Oranim Academic College, the Israel Oceanographic and Limnological Research (IOLR) institution, the Natural History Museum in London, and the Johannes Gutenberg University in Mainz. A close analysis of the remains of a carp-like fish found at the Gesher Benot Ya'aqov (GBY) archaeological site in Israel shows that the fish were cooked roughly 780,000 years ago. Cooking is defined as the ability to process food by controlling the temperature at which it is heated and includes a wide range of methods. Until now, the earliest evidence of cooking dates to approximately 170,000 years ago. The question of when early man began using fire to cook food has been the subject of much scientific discussion for over a century. These findings shed new light on the matter and was published in Nature Ecology and Evolution.

The study was led by a team of researchers: Dr. Irit Zohar, a researcher at TAU's Steinhardt Museum of Natural History and curator of the Beit Margolin Biological Collections at Oranim Academic College, and HU Professor Naama Goren-Inbar, director of the excavation site. The research team also included Dr. Marion Prevost at HU's Institute of Archaeology; Prof. Nira Alperson-Afil at BIU's Department for Israel Studies and Archaeology; Dr. Jens Najorka of the Natural History Museum in London; Dr. Guy Sisma-Ventura of the Israel Oceanographic and Limnological Research Institute; Prof. Thomas Tütken of the Johannes Gutenberg University in Mainz and Prof. Israel Hershkovitz at TAU's Faculty of Medicine.

Dr. Zohar and Dr. Prevost: "This study demonstrates the huge importance of fish in the life of prehistoric humans, for their diet and economic stability. Further, by studying the fish remains found at Gesher Benot Ya'aqob we were able to reconstruct, for the first time, the fish population of the ancient Hula Lake and to show that the lake held fish species that became extinct over time. These species included giant barbs (carp like fish) that reached up to 2 meters in length. The large quantity of fish remains found at the site proves their frequent consumption by early humans, who developed special cooking techniques. These new findings demonstrate not only the importance of freshwater habitats and the fish they contained for the sustenance of prehistoric man, but also illustrate prehistoric humans' ability to control fire in order to cook food, and their understanding the benefits of cooking fish before eating it."

In the study, the researchers focused on pharyngeal teeth (used to grind up hard food such as shells) belonging to fish from the carp family. These teeth were found in large quantities at different archaeological strata at the site. By studying the structure of the crystals that form the teeth enamel (whose size increases through exposure to heat), the researchers were able to prove that the fish caught at the ancient Hula Lake, adjacent to the site, were exposed to temperatures suitable for cooking, and were not simply burned by a spontaneous fire.

Until now, evidence of the use of fire for cooking had been limited to sites that came into use much later than the GBY site -- by some 600,000 years, and ones most are associated with the emergence of our own species, homo sapiens.

Prof. Goren-Inbar added: "The fact that the cooking of fish is evident over such a long and unbroken period of settlement at the site indicates a continuous tradition of cooking food. This is another in a series of discoveries relating to the high cognitive capabilities of the Acheulian hunter-gatherers who were active in the ancient Hula Valley region. These groups were deeply familiar with their environment and the various resources it offered them. Further, it shows they had extensive knowledge of the life cycles of different plant and animal species. Gaining the skill required to cook food marks a significant evolutionary advance, as it provided an additional means for making optimal use of available food resources. It is even possible that cooking was not limited to fish, but also included various types of animals and plants."

Prof. Hershkovitz and Dr. Zohar note that the transition from eating raw food to eating cooked food had dramatic implications for human development and behavior. Eating cooked food reduces the bodily energy required to break down and digest food, allowing other physical systems to develop. It also leads to changes in the structure of the human jaw and skull. This change freed humans from the daily, intensive work of searching for and digesting raw food, providing them free time in which to develop new social and behavioral systems. Some scientists view eating fish as a milestone in the quantum leap in human cognitive evolution, providing a central catalyst for the development of the human brain. They claim that eating fish is what made us human. Even today, it is widely known that the contents of fish flesh, such as omega-3 fatty acids, zinc, iodine and more, contribute greatly to brain development.

The research team believe that the location of freshwater areas, some of them in areas that have long since dried up and become arid deserts, determined the route of the migration of early man from Africa to the Levant and beyond. Not only did these habitats provide drinking water and attracted animals to the area but catching fish in shallow water is a relatively simple and safe task with a very high nutritional reward.

The team posits that exploiting fish in freshwater habitats was the first step on prehistoric humans' route out of Africa. Early man began to eat fish around 2 million years ago but cooking fish -- as found in this study -- represented a real revolution in the Acheulian diet and is an important foundation for understanding the relationship between man, the environment, climate, and migration when attempting to reconstruct the history of early humans.

It should be noted that evidence of the use of fire at the site -- the oldest such evidence in Eurasia -- was identified first by BIU's Prof. Nira Alperson-Afil. "The use of fire is a behavior that characterizes the entire continuum of settlement at the site," she explained. "This affected the spatial organization of the site and the activity conducted there, which revolved around fireplaces." Alperson-Afil's research of fire at the site was revolutionary for its time and showed that the use of fire began hundreds of thousands of years before previously thought.

HU's Goren-Inbar added that the archaeological site of GBY documents a continuum of repeated settlement by groups of hunter-gatherers on the shores of the ancient Hula Lake which lasting tens of thousands of years. "These groups made use of the rich array of resources provided by the ancient Hula Valley and left behind a long settlement continuum with over 20 settlement strata," Goren-Inbar explained. The excavations at the site have uncovered the material culture of these ancient hominins, including flint, basalt, and limestone tools, as well as their food sources, which were characterized by a rich diversity of plant species from the lake and its shores (including fruit, nuts, and seeds) and by many species of land mammals, both medium-sized and large.

Dr. Jens Najorka of the Natural History Museum in London explained: "In this study, we used geochemical methods to identify changes in the size of the tooth enamel crystals, as a result of exposure to different cooking temperatures. When they are burnt by fire, it is easy to identify the dramatic change in the size of the enamel crystals, but it is more difficult to identify the changes caused by cooking at temperatures between 200 and 500 degrees Celsius. The experiments I conducted with Dr. Zohar allowed us to identify the changes caused by cooking at low temperatures. We do not know exactly how the fish were cooked but given the lack of evidence of exposure to high temperatures, it is clear that they were not cooked directly in fire, and were not thrown into a fire as waste or as material for burning."

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Ancient disease has potential to regenerate livers

Leprosy is one of the world's oldest and most persistent diseases but the bacteria that cause it may also have the surprising ability to grow and regenerate a vital organ.

Scientists have discovered that parasites associated with leprosy can reprogramme cells to increase the size of a liver in adult animals without causing damage, scarring or tumors.

The findings suggest the possibility of adapting this natural process to renew ageing livers and increase healthspan -- the length of time living disease-free -- in humans.

Experts say it could also help regrow damaged livers, thereby reducing the need for transplantation, which is currently the only curative option for people with end-stage scarred livers.

Previous studies promoted the regrowth of mouse livers by generating stem cells and progenitor cells -- the step after a stem cell that can become any type of cell for a specific organ -- via an invasive technique that often resulted in scarring and tumour growth.

To overcome these harmful side-effects, Edinburgh researchers built on their previous discovery of the partial cellular reprogramming ability of the leprosy-causing bacteria, Mycobacterium leprae.

Working with the US Department of Health and Human Services in Baton Rouge, Louisiana, the team infected 57 armadillos -- a natural host of leprosy bacteria -- with the parasite and compared their livers with those of uninfected armadillos and those that were found to be resistant to infection.

They found that the infected animals developed enlarged -- yet healthy and unharmed -- livers with the same vital components, such as blood vessels, bile ducts and functional units known as lobules, as the uninfected and resistant armadillos.

The team believe the bacteria 'hijacked' the inherent regenerative ability of the liver to increase the organ's size and, therefore, to provide it with more cells within which to increase.

They also discovered several indicators that the main kinds of liver cells -- known as hepatocytes -- had reached a "rejuvenated" state in the infected armadilllos.

Livers of the infected armadillos also contained gene expression patterns -- the blueprint for building a cell -- similar to those in younger animals and human fetal livers.

Genes related to metabolism, growth and cell proliferation were activated and those linked with aging were downregulated, or suppressed.

Scientists think this is because the bacteria reprogramed the liver cells, returning them to the earlier stage of progenitor cells, which in turn became new hepatocytes and grow new liver tissues.

The team are hopeful that the discovery has the potential to help develop interventions for aging and damaged livers in humans. Liver diseases currently result in two million deaths a year worldwide.

The findings have been published in the journal Cell Reports Medicine. This work has been funded by the UK's Medical Research Council and the US National Institutes of Health and National Institute of Allergy and Infectious Diseases.

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2400 new eyes on the sky to see cosmic rainbows

The Subaru Telescope successfully demonstrated engineering first light with a new instrument that will use about 2400 fiberoptic cables to capture the light from heavenly objects. Full operation is scheduled to start around 2024. The ability to observe thousands of objects simultaneously will provide unprecedented amounts of data to fuel Big Data Astronomy in the coming decade.

In addition to cameras, astronomers also use instruments known as spectrographs to study celestial object. A spectrograph breaks the light from an object into its component colors, in other words it creates a precise rainbow. Studying the strengths of the different colors in the rainbow from an object can tell astronomers various details about the object such as its motion, temperature, and chemical composition.

This new instrument, called PFS (Prime Focus Spectrograph), breaks visible light rainbows into two components: the red side and the blue side. So it might be more correct to refer to the data sets as half-rainbows. Combined with a third kind of detector which can see the infrared light invisible to humans, that makes one-and-a-half rainbows for an object studied with all three types of detectors.

Together with a widefield camera (HSC: Hyper Suprime-Cam), PFS will help launch the Subaru Telescope 2.0 project which will reveal the nature of dark matter and dark energy, structure formation in the Universe, and the physical processes of galaxy formation and evolution.

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Was I happy then? Our current feelings can interfere with memories of past well-being

Many of us spend our lives chasing "happiness," a state of contentment that is more difficult for some to achieve than others. Research in Psychological Science suggests that one reason happiness can seem so elusive is that our current feelings can interfere with memories of our past well-being.

"Happy people tend to overstate the improvement of their life satisfaction over time, whereas unhappy ones tend to overstate the deterioration of their level of happiness. This indicates a certain confusion between feeling happy and feeling better," explained authors Alberto Prati (University College London and University of Oxford) and Claudia Senik (Sorbonne University) in an interview.

Prati and Senik analyzed data from four longitudinal surveys to investigate how our current feelings influence our memories of past happiness.

First, Prati and Senik analyzed existing data from the German Socio-Economic Panel's ongoing survey of German citizens' well-being, focusing on responses from 11,056 participants between 2006 and 2016. Each year, participants had reported how satisfied they were with their life on a scale of 1 to 10. In 2016, respondents were also asked to select one of nine line graphs that best reflected the trajectory of their life satisfaction over the past decade.

Participants' graph selections were generally reflective of their past responses, Prati and Senik wrote in the article. People who reported higher current life satisfaction were more likely to select a chart illustrating continuous improvement. People with middling satisfaction were likelier to select a chart illustrating slight improvement, and people who reported lower current life satisfaction were likelier to select a chart illustrating dips in their well-being.

"People are able to recall how they used to feel about their life, but they also tend to mix this memory with the way they currently feel," Prati and Senik said.

The researchers further investigated this trend using data from 20,269 participants in the 1997 to 2009 British Household Panel Survey. As part of the survey, respondents had reported their current life satisfaction on a scale of 1 to 7 as well as whether they felt more, less, or equally satisfied as they recalled being the year before.

Around half of respondents accurately recalled how their current life satisfaction compared with their report the previous year. But, as with the German data, inaccurate recollections appeared to be influenced by current satisfaction.

These results held at the aggregate level, too. When Prati and Senik analyzed 18,589 quarterly responses to a National Institute of Statistics and Economic Studies survey, they found that French participants recalled, on average, being less happy a year ago than they had actually reported on the survey.

American respondents to the 1971, 1976, 2001, and 2006 Gallup Poll Social Series demonstrated the same tendency to underreport their past happiness, with the averaged responses of 4,000 participants suggesting that Americans remembered being less happy 5 years ago than they had reported at the time.

"It thus seems that feeling happy today implies feeling better than yesterday," Prati and Senik wrote. "This recall structure has implications for motivated memory and learning and could explain why happy people are more optimistic, perceive risks to be lower, and are more open to new experiences."

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How photoelectrodes change in contact with water

Every green leaf is able to convert solar energy into chemical energy, storing it in chemical compounds. However, an important sub-process of photosynthesis can already be technically imitated -- solar hydrogen production: Sunlight generates a current in a so-called photoelectrode that can be used to split water molecules. This produces hydrogen, a versatile fuel that stores solar energy in chemical form and can release it when needed.

Photoelectrodes with many talents

At the HZB Institute for Solar Fuels, many teams are working on this vision. The focus of their research is on producing efficient photoelectrodes. These are semiconductors that remain stable in aqueous solutions and are highly active: Not only can they convert sunlight into electrical current, but they may also act as catalysts to accelerate the splitting of water. Among the best candidates for inexpensive and efficient photoelectrodes is bismuth vanadate (BiVO4).

What happens when in water?

"Basically, we know that just by immersing bismuth vanadate in the aqueous solution the chemical composition of the surface changes," says Dr. David Starr of the HZB Institute for Solar Fuels. And his colleague Dr. Marco Favaro adds: "Although there are a great many studies on BiVO4, it has not been clear until now exactly what implications this has on the surface electronic properties once they come into contact with the water molecules." In this work, they have now investigated this question.

Doped BiVO4 under water vapor

They studied single crystals of BiVO4 doped with molybdenum under water vapor with resonant ambient pressure photoemission spectroscopy at the Advanced Light Source at Lawrence Berkeley National Laboratory. A team led by Giulia Galli at the University of Chicago then performed density functional theory calculations to help interpret the data and to untangle the contributions of individual elements and electron orbitals to the electronic states.

Polarons on the surface detected

"In situ resonant photoemission has allowed us to understand how the electronic properties of our BiVO4 crystals changed upon water adsorption," Favaro says. The combination of measurements and calculations showed that due to excess charge, generated by either doping or defects on certain surfaces of the crystal, so-called polarons may form: negatively charged localized states, where water molecules can easily attach and then dissociate. The hydroxyl groups formed via water dissociation help to stabilize further polaron formation. "The excess electrons are localized as polarons at VO4 units on the surface," Starr summarizes the results.

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How COVID-19 causes neurological damage

It's not uncommon for people to lose their sense of taste and smell due to a Covid-19 infection. In others, the disease has had an even stronger impact on the nervous system, with effects ranging from lasting concentration problems to strokes. Now, researchers led by Professor Gregor Hutter from the Department of Biomedicine at the University of Basel and University Hospital of Basel have reported new insights into the development of "neuro-Covid" in the journal Nature Communications.

Specifically, the team investigated how different severities of neuro-COVID can be detected and predicted by analyzing the cerebrospinal fluid and blood plasma of affected individuals. Their findings also offer some indications of how to prevent neurological damage due to Covid-19.

The study included 40 Covid-19 patients with differing degrees of neurological symptoms. In order to identify typical changes associated with neuro-Covid, the team of researchers compared these individuals' cerebrospinal fluid and blood plasma with samples from a control group. They also measured the brain structures of test subjects and surveyed participants 13 months after their illness in order to identify any lasting symptoms.

Holes in the blood-brain barrier

Particularly in the group with the most serious neurological symptoms, the researchers identified a link with an excessive immune response. On the one hand, affected individuals showed indications of impairment of the blood-brain barrier, which the study's authors speculate was probably triggered by a "cytokine storm" -- a massive release of pro-inflammatory factors in response to the virus.

On the other hand, the researchers also found antibodies that targeted parts of the body's own cells -- in other words, signs of an autoimmune reaction -- as a result of the excessive immune response. "We suspect that these antibodies cross the porous blood-brain barrier into the brain, where they cause damage," explains Hutter. They also identified excessive activation of the immune cells specifically responsible for the brain -- the microglia.

Blood test as a long-term objective

In a further step, Hutter and his team investigated whether the severity of neurological symptoms is also perceptible in brain structures. Indeed, they found that people with serious neuro-Covid symptoms had a lower brain volume than healthy participants at specific locations in the brain and particularly at the olfactory cortex -- that is, the area of the brain responsible for smell.

"We were able to link the signature of certain molecules in the blood and cerebrospinal fluid to an overwhelming immune response in the brain and reduced brain volume in certain areas, as well as neurological symptoms," says Hutter, adding that it is now important to examine these biomarkers in a greater number of participants. The aim would be to develop a blood test that can already predict serious cases, including neuro-Covid and long Covid, at the start of an infection.

Targets for preventing consequential damage

These same biomarkers point to potential targets for drugs aimed at preventing consequential damage due to a Covid-19 infection. One of the biomarkers identified in blood, the factor MCP-3, plays a key role in the excessive immune response, and Hutter believes there is the potential to inhibit this factor medicinally.

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Searching for traces of dark matter with neutron spin clocks

With the use of a precision experiment developed at the University of Bern, an international research team has succeeded in significantly narrowing the scope for the existence of dark matter. The experiment was carried out at the European Research Neutron Source at the Institute Laue-Langevin in France, and makes an important contribution to the search for these particles, of which little is known.

Cosmological observations of the orbits of stars and galaxies enable clear conclusions to be drawn about the attractive gravitational forces that act between the celestial bodies. The astonishing finding: visible matter is far from sufficient for being able to explain the development or movements of galaxies. This suggests that there exists another, so far unknown, type of matter. Accordingly, in the year 1933, the Swiss physicist and astronomer Fritz Zwicky inferred the existence of what is known now as dark matter. Dark matter is a postulated form of matter which isn't directly visible but interacts via gravity, and consists of approximately five times more mass than the matter with which we are familiar.

Recently, following a precision experiment developed at the Albert Einstein Center for Fundamental Physics (AEC) at the University of Bern, an international research team succeeded in significantly narrowing the scope for the existence of dark matter. With more than 100 members, the AEC is one of the leading international research organisations in the field of particle physics. The findings of the team, led by Bern, have now been published in the journal Physical Review Letters.

The mystery surrounding dark matter

"What dark matter is actually made of is still completely unclear," explains Ivo Schulthess, a PhD student at the AEC and the lead author of the study. What is certain, however, is that it is not made from the same particles that make up the stars, planet Earth or us humans. Worldwide, increasingly sensitive experiments and methods are being used to search for possible dark matter particles -- until now, however, without success.

Certain hypothetical elementary particles, known as axions, are a promising category of possible candidates for dark matter particles. An important advantage of these extremely lightweight particles is that they could simultaneously explain other important phenomena in particle physics which have not yet been understood.

Bern experiment sheds light on the darkness

"Thanks to many years of expertise, our team has succeeded in designing and building an extremely sensitive measurement apparatus -- the Beam EDM experiment," explains Florian Piegsa, Professor for Low Energy and Precision Physics at the AEC, who was awarded one of the prestigious ERC Starting Grants from the European Research Council in 2016 for his research with neutrons. If the elusive axions actually exist, they should leave behind a characteristic signature in the measurement apparatus.

"Our experiment enables us to determine the rotational frequency of neutron spins, which move through a superposition of electric and magnetic fields," explains Schulthess. The spin of each individual neutron acts as a kind of compass needle, which rotates due to a magnetic field similarly to the second hand of a wristwatch -- but nearly 400,000 times faster. "We precisely measured this rotational frequency and examined it for the smallest periodic fluctuations which would be caused by the interactions with the axions," explains Piegsa. The results of the experiment were clear: "The rotational frequency of the neutrons remained unchanged, which means that there is no evidence of axions in our measurement," says Piegsa.

Parameter space successfully narrowed down

The measurements, which were carried out with researchers from France at the European Research Neutron Source at the Institute Laue-Langevin, allowed for the experimental exclusion of a previously completely unexplored parameter space of axions. It also proved possible to search for hypothetical axions which would be more than 1,000 times heavier than was previously possible with other experiments.

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Earth-sun distance dramatically alters seasons in the equatorial Pacific in a 22,000-year cycle

Weather and climate modelers understand pretty well how seasonal winds and ocean currents affect El Niño patterns in the eastern equatorial Pacific Ocean, impacting weather across the United States and sometimes worldwide.

But new computer simulations show that one driver of annual weather cycles in that region -- in particular, a cold tongue of surface waters stretching westward along the equator from the coast of South America -- has gone unrecognized: the changing distance between Earth and the sun.

The cold tongue, in turn, influences the El Niño-Southern Oscillation (ENSO), which impacts weather in California, much of North America, and often globally.

The Earth-sun distance slowly varies over the course of the year because Earth's orbit is slightly elliptical. Currently, at its closest approach -- perihelion -- Earth is about 3 million miles closer to the sun than at its farthest point, or aphelion. As a result, sunlight is about 7% more intense at perihelion than at aphelion.

Research led by the University of California, Berkeley, demonstrates that the slight yearly change in our distance from the sun can have a large effect on the annual cycle of the cold tongue. This is distinct from the effect of Earth's axial tilt on the seasons, which is currently understood to cause the annual cycle of the cold tongue.

Because the period of the annual cycle arising from the tilt and distance effects are slightly different, their combined effects vary over time, said lead researcher John Chiang, UC Berkeley professor of geography.

"The curious thing is that the annual cycle from the distance effect is slightly longer than that for tilt -- around 25 minutes, currently -- so over a span of about 11,000 years, the two annual cycles go from being in phase to out of phase, and the net seasonality undergoes a remarkable change, as a result," Chiang said.

Chiang noted that the distance effect is already incorporated into climate models -- though its effect on the equatorial Pacific was not recognized until now -- and his findings will not alter weather predictions or climate projections. But the 22,000-year phase cycle may have had long-term, historical effects. Earth's orbital precession is known to have affected the timing of the ice ages, for example.

The distance effect -- and its 22,000-year variation -- also may affect other weather systems on Earth. The ENSO, which also originates in the equatorial Pacific, is likely affected because its workings are closely tied to the seasonal cycle of the cold tongue.

"Theory tells us that the seasonal cycle of the cold tongue plays a key role in the development and termination of ENSO events," said Alyssa Atwood, a former UC Berkeley postdoctoral fellow who is now an assistant professor at Florida State University in Tallahassee. "Because of this, many of ENSO's key characteristics are synced to the seasonal cycle."

For example, ENSO events tend to peak during Northern Hemisphere winters, she said, and they don't typically persist beyond northern or boreal spring months, which scientists refer to as the "spring predictability barrier." Because of these linkages, it is reasonable to expect that the distance effect could also have a major impact on ENSO -- something that should be examined in future studies.

"Very little attention has been paid to the cold tongue seasonal cycle because most people think it's solved. There's nothing interesting there," Chiang said. "What this research shows is that it's not solved. There's still a mystery there. Our result also begs the question whether other regions on Earth may also have a significant distance effect contribution to their seasonal cycle."

"We learn in science classes as early as grade school that the seasons are caused by the tilt of Earth's axis," added co-author Anthony Broccoli of Rutgers University. "This is certainly true and has been well understood for centuries. Although the effect of the Earth-sun distance has also been recognized, our study indicates that this 'distance effect' may be a more important effect on climate than had been recognized previously."

Chiang, Atwood and Broccoli and their colleagues reported their findings today in the journal Nature.

Two distinct yearly cycles affect Pacific cold tongue

The main driver of global weather changes is seasonal change. Earth's equator is tilted relative to its orbit around the sun, so the Northern and Southern hemispheres are illuminated differently. When the sun shines directly overhead in the north, it's warmer in the north and colder in the south, and vice versa.

These yearly changes have major effects on the Pacific equatorial trade winds, which blow from southeast to northwest across the south and equatorial Pacific and push surface waters westward, causing upwelling of cold water along the equator that creates a tongue of cold surface water that stretches from Ecuador across the Pacific -- almost one-quarter the circumference of the planet.

The yearly hemispheric changes in seasonal temperature alters the strength of the trades, and thus cause a yearly cycle in the temperature of the cold tongue. This, in turn, has a major influence on ENSO, which typically peaks during Northern Hemisphere winter.

The occurrence of El Niño -- or its opposite, La Niña -- helps determines whether California and the West Coast will have a wet or dry winter, but also whether the Midwest and parts of Asia will have rain or drought.

"In studying past climates, much effort has been dedicated to trying to understand if variability in the tropical Pacific Ocean -- that is, the El Niño/La Niña cycle -- has changed in the past," Broccoli said. "We chose to focus instead on the yearly cycle of ocean temperatures in the eastern Pacific cold tongue. Our study found that the timing of perihelion -- that is, the point at which the earth is closest to the sun -- has an important influence on climate in the tropical Pacific."

In 2015, Broccoli, co-director of the Rutgers Climate Institute, along with his then-graduate student Michael Erb, employed a computer climate model to show that the distance changes caused by Earth's elliptical orbit dramatically altered the cold tongue yearly cycle. But climate modelers mostly ignored the result, Chiang said.

"Our field is focused on El Niño, and we thought that the seasonal cycle was solved. But then we realized that the result by Erb and Broccoli challenged this assumption," he said.

Chiang and his colleagues, including Broccoli and Atwood, examined similar simulations using four different climate models and confirmed the result. But the team went further to show how the distance effect works.

Earth's 'marine' and 'continental' hemispheres

The key distinction is that changes in the sun's distance from Earth don't affect the Northern and Southern hemispheres differently, which is what gives rise to the seasonal effect due to Earth's axial tilt. Instead, they warm the eastern "continental hemisphere" dominated by the North and South American and African and Eurasian landmasses, more than it warms the Western Hemisphere -- what he calls the marine hemisphere, because it is dominated by the Pacific Ocean.

"The traditional way of thinking about monsoons is that the Northern Hemisphere warms up relative to the Southern Hemisphere, generating winds onto land that bring monsoon rains," Chiang said. "But here, we're actually talking about east-west, not north-south, temperature differences that cause the winds. The distance effect is operating through the same mechanism as the seasonal monsoon rains, but the wind changes are coming from this east-west monsoon."

The winds generated by this differential heating of the marine and continental hemispheres alter the yearly variation of the easterly trades in the western equatorial Pacific, and thereby the cold tongue.

"When Earth is closest to the sun, these winds are strong. In the offseason, when the sun is at its furthest, these winds become weak," Chiang said. "Those wind changes are then propagated to the Eastern Pacific through the thermocline, and basically it drives an annual cycle of the cold tongue, as a result."

Today, Chiang said, the distance effect on the cold tongue is about one-third the strength of the tilt effect, and they enhance one another, leading to a strong annual cycle of the cold tongue. About 6,000 years ago, they canceled one another, yielding a muted annual cycle of the cold tongue. In the past, when Earth's orbit was more elliptical, the distance effect on the cold tongue would have been larger and could have led to a more complete cancellation when out of phase.

Though Chiang and his colleagues did not examine the effect of such a cancellation, this would potentially have had a worldwide effect on weather patterns.

Chiang emphasized that the distance effect on climate, while clear in climate model simulations, would not be evident from observations because it cannot be readily distinguished from the tilt effect.

"This study is purely model based. So, it is a prediction," he said. "But this behavior is reproduced by a number of different models, at least four. And what we did in this study is to explain why this happens. And in the process, we've discovered another annual cycle of the cold tongue that's driven by Earth's eccentricity."

Atwood noted that, unlike the robust changes to the cold tongue seasonal cycle, changes to ENSO tend to be model-dependent.

"While ENSO remains a challenge for climate models, we can look beyond climate model simulations to the paleoclimate record to investigate the connection between changes in the annual cycle of the cold tongue and ENSO in the past," she said. "To date, paleoclimate records from the tropical Pacific have largely been interpreted in terms of past changes in ENSO, but our study underscores the need to separate changes in the cold tongue annual cycle from changes in ENSO."

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