Burning candles and fumes from cooking is harmful for people with mild asthma

A cosy set table, a nice steak in the pan, and romantic candlelight may sound like the start of a lovely evening. However, a new study from the Department of Public Health at Aarhus University suggests that you should be cautious about inhaling too much of the cosy atmosphere. Karin Rosenkilde Laursen, a postdoc at the department and co-author of the study, says:

"Our study shows that indoor air pollution caused by fumes from cooking and burning candles can lead to adverse health effects such as irritation and inflammation in young individuals with mild asthma. Among other things, we've found indications of DNA damage and signs of inflammation in the blood."

When we turn on the oven, place a pan on the hob, or light candles, ultrafine particles and gases are produced, which we then inhale. Previous studies have shown that these particles and gases can be detrimental to health. What sets this study apart is that the researchers have focused on the effects on young individuals with mild asthma, aged between 18 and 25, says Karin Rosenkilde Laursen:

"In the study, we observed that even very young individuals with mild asthma can experience discomfort and adverse effects if the room is not adequately ventilated during cooking or when burning candles. Young people are generally fitter and more resilient than older and middle-aged individuals. Therefore, it is concerning that we observed a significant impact from the particles on this particularly young age group."

But not only people diagnosed with asthma need to keep an eye on the indoor climate, she says.

"Even though the study focused on young asthmatics, its findings are interesting and relevant for all of us. Winter is approaching, a time when we tend to light many candles and perhaps are less likely to open doors and windows while cooking. By prioritising a healthier indoor climate, even when we're cosying up indoors, we may be able to help reduce the incidence of serious lung and cardiovascular diseases, as well as cancer."

Karin Rosenkilde Laursen plans to follow up this study with another examining how emissions from cooking and candles affect healthy adults.

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Telescopes help unravel pulsar puzzle

With a remarkable observational campaign that involved 12 telescopes both on the ground and in space, including three European Southern Observatory (ESO) facilities, astronomers have uncovered the strange behaviour of a pulsar, a super-fast-spinning dead star. This mysterious object is known to switch between two brightness modes almost constantly, something that until now has been an enigma. But astronomers have now found that sudden ejections of matter from the pulsar over very short periods are responsible for the peculiar switches.

"We have witnessed extraordinary cosmic events where enormous amounts of matter, similar to cosmic cannonballs, are launched into space within a very brief time span of tens of seconds from a small, dense celestial object rotating at incredibly high speeds," says Maria Cristina Baglio, researcher at New York University Abu Dhabi, affiliated with the Italian National Institute for Astrophysics (INAF), and the lead author of the paper published today in Astronomy & Astrophysics.

A pulsar is a fast-rotating, magnetic, dead star that emits a beam of electromagnetic radiation into space. As it rotates, this beam sweeps across the cosmos -- much like a lighthouse beam scanning its surroundings -- and is detected by astronomers as it intersects the line of sight to Earth. This makes the star appear to pulse in brightness as seen from our planet.

PSR J1023+0038, or J1023 for short, is a special type of pulsar with a bizarre behaviour. Located about 4500 light-years away in the Sextans constellation, it closely orbits another star. Over the past decade, the pulsar has been actively pulling matter off this companion, which accumulates in a disc around the pulsar and slowly falls towards it.

Since this process of accumulating matter began, the sweeping beam virtually vanished and the pulsar started incessantly switching between two modes. In the 'high' mode, the pulsar gives off bright X-rays, ultraviolet and visible light, while in the 'low' mode it's dimmer at these frequencies and emits more radio waves. The pulsar can stay in each mode for several seconds or minutes, and then switch to the other mode in just a few seconds. This switching has thus far puzzled astronomers.

"Our unprecedented observing campaign to understand this pulsar's behaviour involved a dozen cutting-edge ground-based and space-borne telescopes," says Francesco Coti Zelati, a researcher at the Institute of Space Sciences, Barcelona, Spain, and co-lead author of the paper. The campaign included ESO's Very Large Telescope (VLT) and ESO's New Technology Telescope (NTT), which detected visible and near-infrared light, as well as the Atacama Large Millimeter/submillimeter Array (ALMA), in which ESO is a partner. Over two nights in June 2021, they observed the system make over 280 switches between its high and low modes.

"We have discovered that the mode switching stems from an intricate interplay between the pulsar wind, a flow of high-energy particles blowing away from the pulsar, and matter flowing towards the pulsar," says Coti Zelati, who is also affiliated with INAF.

In the low mode, matter flowing towards the pulsar is expelled in a narrow jet perpendicular to the disc. Gradually, this matter accumulates closer and closer to the pulsar and, as this happens, it is hit by the wind blowing from the pulsating star, causing the matter to heat up. The system is now in a high mode, glowing brightly in the X-ray, ultraviolet and visible light. Eventually, blobs of this hot matter are removed by the pulsar via the jet. With less hot matter in the disc, the system glows less brightly, switching back into the low mode.

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New research explains 'Atlantification' of the Arctic Ocean

New research by an international team of scientists explains what's behind a stalled trend in Arctic Ocean sea ice loss since 2007. The findings indicate that stronger declines in sea ice will occur when an atmospheric feature known as the Arctic dipole reverses itself in its recurring cycle.

The many environmental responses to the Arctic dipole are described in a paper published online today in the journal Science. This analysis helps explain how North Atlantic water influences Arctic Ocean climate. Scientists call it Atlantification.

The research is led by professor Igor Polyakov of the University of Alaska Fairbanks College of Natural Science and Mathematics. He is also affiliated with the International Arctic Research Center at UAF.

Co-authors include Andrey V. Pnyushkov, research assistant professor at the International Arctic Research Center; Uma S. Bhatt, atmospheric sciences professor at the UAF Geophysical Institute and UAF College of Natural Science and Mathematics; and researchers from Massachusetts, Washington state, Norway, and Germany.

"This is a multidisciplinary view on what's going on in the Arctic and beyond," Polyakov said of the new research. "Our analysis covered the atmosphere, ocean, ice, changing continents and changing biology in response to climate change."

A wealth of data, including direct instrumental observations, reanalysis products and satellite information going back several decades, shows that the Arctic dipole alternates in an approximately 15-year cycle and that the system is probably at the end of the present regime.

In the Arctic dipole's present "positive" regime, which scientists say has been in place since 2007, high pressure is centered over the Canadian sector of the Arctic and produces clockwise winds. Low pressure is centered over the Siberian Arctic and features counterclockwise winds.

This wind pattern drives upper ocean currents, with year-round effects on regional air temperatures, atmosphere-ice-ocean heat exchanges, sea-ice drift and exports, and ecological consequences.

The authors write that, "Water exchanges between the Nordic seas and the Arctic Ocean are critically important for the state of the Arctic climate system" and that sea ice decline is "a true indicator of climate change."

In analyzing oceanic responses to the wind pattern since 2007, the researchers found decreased flow from the Atlantic Ocean into the Arctic Ocean through the Fram Strait east of Greenland, along with increased Atlantic flow into the Barents Sea, located north of Norway and western Russia.

The new research refers to these alternating changes in the Fram Strait and the Barents Sea as a "switchgear mechanism" caused by the Arctic dipole regimes.

The researchers also found that counterclockwise winds from the low-pressure region under the current positive Arctic dipole regime drive freshwater from Siberian rivers into the Canadian sector of the Arctic Ocean.

This westward movement of freshwater from 2007 to 2021 helped slow the overall loss of sea ice in the Arctic compared to 1992 through 2006. The freshwater layer's depth increased, making it too thick and stable to mix with the heavier saltwater below. The thick layer of freshwater prevents the warmer saltwater from melting sea ice from the bottom.

The authors write that the switchgear mechanism regulating inflows of sub-Arctic waters has "profound" impacts on marine life. It can lead to potentially more suitable living conditions for sub-Arctic boreal species near the eastern part of the Eurasian Basin, relative to its western part.

"We are beyond the peak of the currently positive Arctic dipole regime, and at any moment it could switch back again," Polyakov said. "This could have significant climatological repercussions, including a potentially faster pace of sea-ice loss across the entire Arctic and sub-Arctic climate systems."

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Unraveling the long history of breast cancer formation

From the early stages of cell mutations starting in puberty to their manifestations as breast cancer in later years, the entire process has remained shrouded in mystery.

Now, a team of researchers at Kyoto University has revealed the mechanism by which breast cancer is formed in the cells of the mammalian epithelium, whose main function is to secrete milk.

According to the team's first analysis, approximately 20 mutations accumulate annually in each epithelial cell until menopause. After menopause, however, the mutation rate significantlydecreases.

"Additionally, our results suggest that estrogen influences mutation accumulation in mammary epithelium, which correlates with our discovery of decreased accumulation after childbirth," says corresponding author Seishi Ogawa of KyotoU's Graduate School of Medicine.

As 70% of breast cancers are understood to be estrogen-sensitive, Ogawa's team may shed light on estrogen's role in the initiation of breast cancer.

Further investigation of the genetic relationship between breast cancer, its surrounding lesions, and normal epithelial cells led to mapping breast cancer's translocation-positive expansion. During this expansion process, cells of multiple origins that would subsequently develop breast cancer manifested themselves at the average age of 30. Previous studies have focused on driver mutations -- the genetic changes in cells that are already cancerous -- leading to abnormal growth. But these findings only paint a partial picture of the process and do not reveal the timing and order of driver mutations or cancer formation.

"Normal-looking tissues may already contain numerous populations of non-cancer cells -- or clones -- that have acquired mutations in cancer-related genes," says co-author author Tomomi Nishimuraof KyotoU's Graduate School of Medicine.

After examining the similarities and differences in the mutations of both cancer and non-cancer lesions originating from the clones, the team reconstructed an evolutionary tree to visualize the unique pattern of cancer evolution.

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Quantum discovery offers glimpse into other-worldly realm

The field of quantum physics is rife with paths leading to tantalising new areas of study, but one rabbit hole offers a unique vantage point into a world where particles behave differently -- through the proverbial looking glass.

Dubbed the 'Alice ring' after Lewis Carroll's world-renowned stories on Alice's Adventures in Wonderland, the appearance of this object verifies a decades-old theory on how monopoles decay. Specifically, that they decay into a ring-like vortex, where any other monopoles passing through its centre are flipped into their opposite magnetic charges.

Published in Nature Communications on August 29, these findings mark the latest discovery in a string of work that has spanned the collaborative careers of Aalto University Professor Mikko Möttönen and Amherst College Professor David Hall.

'This was the first time our collaboration was able to create Alice rings in nature, which was a monumental achievement,' Möttönen said.

'This fundamental research opens new doors into understanding how these structures and their analogues in particle physics function in the universe,' Hall added.

The long-standing relationship, titled the Monopole Collaboration, initially proved the existence of a quantum analogue of the magnetic monopole in 2014, isolated quantum monopoles in 2015, and eventually observed one decay into the other in 2017.

Monopoles remain an elusive concept in the arena of quantum physics. As the name suggests, monopoles are the solitary counterpart of dipoles, which carry a positive charge at their north pole and a negative charge at the south. In contrast, a monopole carries only either a positive or negative charge.

While the concept sounds simple, realising a true monopole has proven to be a career-defining task. Here's how the Monopole Collaboration has done it: they manipulated a gas of rubidium atoms prepared in a nonmagnetic state near absolute zero temperature. Under these extreme conditions, they were then able to create a monopole by steering a zero point of a three-dimensional magnetic field into the quantum gas.

Laying theoretical groundwork

These quantum monopoles are ephemeral by nature, decaying a few milliseconds after their creation. It is within this instability that the Alice ring takes shape.

'Think of the monopole as an egg teetering at the top of a hill,' Möttönen said. 'The slightest perturbations can send it crashing down. In the same way, monopoles are subject to noise that triggers their decay into Alice rings.'

While monopoles are short-lived, the research group simulated stable Alice rings for as long as 84 milliseconds -- over 20 times longer than the monopole lifespan. This leads researchers to be optimistic that future experiments will reveal even more peculiar properties of Alice rings.

'From a distance, the Alice ring just looks like a monopole, but the world takes a different shape when peering through the centre of the ring,' Hall said.

'It is from this perspective that everything seems to be mirrored, as if the ring were a gateway into a world of antimatter instead of matter,' Möttönen added.

In theory, a monopole passing through the centre of an Alice ring would be transformed into an anti-monopole of opposite charge. Correspondingly, the Alice ring's charge would change as well. While this phenomenon has not yet been experimentally observed, Möttönen said the topological structure of Alice rings necessitates this behaviour.

The experimental work was conducted at Amherst College primarily by PhD candidate Alina Blinova and Hall, while Möttönen and his team were responsible for running matching simulations. This way, the two teams were able to confirm the interpretation of the experimental observations.

'It is simply amazing to have such a major discovery as the finale of my PhD work,' Blinova said.

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Groundwater depletion rates in India could triple in coming decades as climate warms, study shows

A new University of Michigan-led study finds that farmers in India have adapted to warming temperatures by intensifying the withdrawal of groundwater used for irrigation. If the trend continues, the rate of groundwater loss could triple by 2080, further threatening India's food and water security.

Reduced water availability in India due to groundwater depletion and climate change could threaten the livelihoods of more than one-third of the country's 1.4 billion residents and has global implications. India recently overtook China to become the world's most populous nation and is the second-largest global producer of common cereal grains including rice and wheat.

"We find that farmers are already increasing irrigation use in response to warming temperatures, an adaptation strategy that has not been accounted for in previous projections of groundwater depletion in India," said study senior author Meha Jain, assistant professor at U-M's School for Environment and Sustainability. "This is of concern, given that India is the world's largest consumer of groundwater and is a critical resource for the regional and global food supply."

The lead author is Nishan Bhattarai of the Department of Geography and Environmental Sustainability at the University of Oklahoma, formerly a postdoctoral researcher in Jain's U-M lab.

The study, scheduled for online publication Sept. 1 in the journal Science Advances, analyzed historical data on groundwater levels, climate and crop water stress to look for recent changes in withdrawal rates due to warming. The researchers also used temperature and precipitation projections from 10 climate models to estimate future rates of groundwater loss across India.

Previous studies have focused on the individual effects of climate change and groundwater depletion on crop production in India. Those studies did not account for farmer decision-making, including how farmers may adapt to changing climate through changes in irrigation decisions.

The new study takes into account the fact that warmer temperatures may increase water demand from stressed crops, which in turn may lead to increased irrigation by farmers.

"Using our model estimates, we project that under a business-as-usual scenario, warming temperatures may triple groundwater depletion rates in the future and expand groundwater depletion hotspots to include south and central India," Bhattarai said.

"Without policies and interventions to conserve groundwater, we find that warming temperatures will likely amplify India's already existing groundwater depletion problem, further challenging India's food and water security in the face of climate change."

Previous studies found that climate change could decrease the yield of staple Indian crops by up to 20% by mid-century. At the same time, the country's groundwater is being depleted at an alarming rate, primarily because of water withdrawal for irrigation.

For the newly published study, the researchers developed a dataset that contains groundwater depths from thousands of wells across India, high-resolution satellite observations that measured crop water stress, and temperature and precipitation records.

Most climate models call for increased temperature, increased monsoon (June through September) precipitation and decreased winter precipitation in India over the coming decades. The U-M-led research team found that warming temperatures coupled with declining winter precipitation more than offset added groundwater recharge from increased monsoon precipitation, resulting in accelerated groundwater declines.

Across various climate-change scenarios, their estimates of groundwater-level declines between 2041 and 2080 were more than three times current depletion rates, on average.

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Bat study reveals how the brain is wired for collective behavior

The same neurons that help bats navigate through space may also help them navigate collective social environments, finds a new study published today in the journal Nature.

Many mammals -- including bats and humans -- are believed to navigate with the help of a brain structure called the hippocampus, which encodes a mental "map" of familiar surroundings. For example, as you walk around your neighborhood or commute to work, individual "place" neurons in the hippocampus fire to indicate where you are.

In the new study, researchers at the University of California, Berkeley, used wireless neural recording and imaging devices to "listen in" on the hippocampal brain activity of groups of Egyptian fruit bats as they flew freely within a large flight room -- often moving among tightly clustered social groups -- while tracking technology recorded the bats' movements.

The researchers were surprised to find that, in this social setting, the bat's place neurons encoded far more information than simply the animal's location. As a bat flew toward a landing spot, the firing of place neurons also contained information about the presence or absence of another bat at that spot. And when another bat was present, the activity of these neurons indicated the identity of the bat they were flying toward.

"This is one of the first papers to show identity representation in a non-primate brain," said study senior author Michael Yartsev, an associate professor of bioengineering and neuroscience at UC Berkeley. "And surprisingly, we found it in the hub of what was supposed to be the brain's GPS.We found that it still acts as a GPS, but one that is also tuned to the social dynamic in the environment."

While not as visually stunning as a school of fish or a murmuration of birds, highly social animals like humans and bats also exhibit forms of collective behavior, said study first author Angelo Forli, a postdoctoral fellow in Yartsev's NeuroBat lab.

"Social animals, like humans, will coordinate in space to achieve different goals," Forli said. "It might be just visiting others. It might be moving together, as in the case of classical collective behaviors or playing a soccer match. Or it might be other forms of cooperation or conflict."

Due to the complexity of the experiment, Forli initially had doubts about whether allowing groups of bats to fly and interact freely would yield results about the neural basis of collective behavior. He was concerned that the movements of the bats and their social interactions might be too random to uncover robust relationships between their neural activity and their behavior.

So he was pleasantly surprised when the bats spontaneously established a handful of specific resting spots within the flight room and followed very similar trajectories when traveling among them. The bats also showed strong preferences for flying toward specific "friend" bats, often landing very close to or even on top of each other.

"We found that if you put together a small group of bats in a room, they would not actually behave randomly, but would show precise patterns of behavior," Forli said. "They would spend time with specific individuals and show specific and stable places where they liked to go."

These precise patterns of behavior allowed Forli to identify not only the neural activity associated with different flight trajectories, but also how the neural activity changed depending on the identity of the bat present at the target location and the movements of other bats.

"By recording just a handful of those neurons from this brain structure, we can really know what the bats were doing in their social space," Yartsev said. "We could find out if they were going to an empty location or to a location where there were other individuals, which is really surprising."

In recent years, Yartsev and his NeuroBat Lab have used a variety of wireless neural recording devices and flight tracking technologies to uncover a number of surprising details about the brain, including how bats' neural activity syncs up while they socialize; how activity in the frontal cortex helps bats identify self vs. others during vocal interactions; how bats' hippocampus maps not only specific locations, but full flight trajectories; and even how stable spatial memories might be stored in the brain.

This new study brings together the team's work on navigation and social behavior, showing how these two things are fundamentally intertwined within the brain. The findings also help illuminate why damage to the hippocampus in humans has been linked to both social and spatial aspects of memory loss in neurodegenerative diseases like Alzheimer's.

"Our episodic memories are a combination of the environment where we are located and our experiences within it -- including, of course, our social experiences," Yartsev said. "Our results are surprising, in the sense that no one has observed this connection before in groups of animals and at the individual neuron level. But they also make sense in that they are very consistent with deficits that people with damage to the hippocampus experience."

Finally, this study highlights a very important point, Yartsev said. While most of the neuroscientific community examines the brain under "simplified" or "artificial" conditions that are often far removed from the natural behavior the brain has evolved to promote, this work demonstrates the power of the natural approach to neuroscience research.

"For half a century, people have been studying place neurons, but 99% of that work has been done in single animals moving in an empty box," Yartsev said. "Our findings suggest that there is a lot that can be learned when neuroscience research focuses on natural behavior."

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Webb reveals new structures within iconic supernova

NASA's James Webb Space Telescope has begun the study of one of the most renowned supernovae, SN 1987A (Supernova 1987A). Located 168,000 light-years away in the Large Magellanic Cloud, SN 1987A has been a target of intense observations at wavelengths ranging from gamma rays to radio for nearly 40 years, since its discovery in February of 1987. New observations by Webb's NIRCam (Near-Infrared Camera) provide a crucial clue to our understanding of how a supernova develops over time to shape its remnant.

This image reveals a central structure like a keyhole. This center is packed with clumpy gas and dust ejected by the supernova explosion. The dust is so dense that even near-infrared light that Webb detects can't penetrate it, shaping the dark "hole" in the keyhole.

A bright, equatorial ring surrounds the inner keyhole, forming a band around the waist that connects two faint arms of hourglass-shaped outer rings. The equatorial ring, formed from material ejected tens of thousands of years before the supernova explosion, contains bright hot spots, which appeared as the supernova's shock wave hit the ring. Now spots are found even exterior to the ring, with diffuse emission surrounding it. These are the locations of supernova shocks hitting more exterior material.

While these structures have been observed to varying degrees by NASA's Hubble and Spitzer Space Telescopes and Chandra X-ray Observatory, the unparalleled sensitivity and spatial resolution of Webb revealed a new feature in this supernova remnant -- small crescent-like structures. These crescents are thought to be a part of the outer layers of gas shot out from the supernova explosion. Their brightness may be an indication of limb brightening, an optical phenomenon that results from viewing the expanding material in three dimensions. In other words, our viewing angle makes it appear that there is more material in these two crescents than there actually may be.

The high resolution of these images is also noteworthy. Before Webb, the now-retired Spitzer telescope observed this supernova in infrared throughout its entire lifespan, yielding key data about how its emissions evolved over time. However, it was never able to observe the supernova with such clarity and detail.

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Evolutionary imbalance explains global plant invasions

Plant species from certain geographic regions are more successful in spreading outside their native ranges than others -- but why? An international research team led by Konstanz ecologists provides answers by exploring how the ecological and evolutionary histories of plants can influence their relationships with humans and their success as invaders.

Human activities -- for example, global trade and travel -- are driving the spread of plants beyond their natural ranges and around the globe. However, not all species benefit equally from these movements; only some are able to successfully establish populations (i.e. naturalize) in new locations. Data on the global distribution of alien plants reveals that plants originating from certain geographic regions are more successful at naturalizing than others.

The evolutionary imbalance hypothesis (EIH) offers possible explanations for this phenomenon, but has not yet been verified on a global scale. An international research team led by biologist Mark van Kleunen from the University of Konstanz has now succeeded in confirming key predictions of this hypothesis using extensive global data. In their study in Nature Ecology & Evolution, the researchers also discover intriguing similarities in the origins of plants that successfully establish populations outside their natural ranges and those that humans have selected for cultivation and economic use -- suggesting that biogeographic factors influence biological and cultural systems in similar ways.

Dating back to Darwin

At its essence, the ideas of the EIH date back to Charles Darwin. "Darwin proposed that geographic barriers divide the Earth's ecosystems into various evolutionary arenas," says Trevor Fristoe, first author of the study and ecologist at the Department of Biology at the University of Konstanz. Within each of these arenas, the organisms inhabiting them would be exposed to unique geographic and ecological conditions that influence the intensity of natural selection. "The result is differences in the absolute fitness for species originating from different regions -- evolutionary imbalances -, and these differences have consequences for which species are more likely to successfully establish in new areas when barriers are removed," Fristoe continues.

Based on these ideas, the EIH makes predictions about the characteristics of global regions that drive the evolution of particularly successful aliens. For example, larger regions should support larger populations and higher genetic diversity to allow for more efficient natural selection. Species-rich regions should serve as intense proving grounds where species must evolve to persist in the presence of a wide variety of competitors and enemies.

The current study tested these predictions on a global scale. For this, the researchers used an unprecedented data set that included the native and alien distributions of over 99 percent of all known seed plants -- over 330,000 species. Consistent with the EIH, they demonstrated that plants originating from vast, species-rich regions are among the most successful alien plants. "Thus, our study confirms two key predictions of the EIH on a global scale," emphasizes Mark van Kleunen, head of the international research team.

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Tiny mineral inclusions picture the chemical exchange between Earth's mantle and atmosphere

Using synchrotron techniques, scientists have unveiled important information on The Great Oxidation Event by studying apatite inclusions in zircon crystals from old magmas with the ESRF -- Extremely Brilliant Source. The results are published in Nature Geoscience.

Around 2.4 billion years ago, a pivotal moment in Earth's history took place: The Great Oxidation Event. During this period, a significant amount of oxygen accumulated in the atmosphere. This surge in oxygen production led to a dramatic shift in the composition of the atmosphere, altering the chemistry of the planet. The event marked a turning point as oxygen levels rose, enabling the development of more complex multicellular life forms and fundamentally reshaping Earth's ecosystems.

Plate tectonics are an effective mechanism for the cycling and interchange of elements among Earth's surface, atmosphere, and mantle. As mountains undergo weathering and erosion through interactions with water and the atmosphere, they break down into sediments. These sediments are then partially returned to the mantle through subduction processes (one tectonic plate sinking beneath another). The formation of magmas in the mantle above subduction zones provides a unique opportunity to explore how the atmosphere could have impacted the mantle by assimilating materials from subducted sediments, offering insights into this intriguing geological relationship.

Scientists have long tried to study the interaction between atmosphere and the Earth's mantle. The mission is already complicated to be accomplished in the modern Earth, and even more so in the early Earth, when the atmosphere and plate tectonics were changing at rapid rates. A team led by the University of Montpellier and University of Portsmouth teamed up with the ESRF -- The European Synchrotron- and found a way to overcome obstacles by studying apatite inclusions in zircon from subduction zones.

"In 2017, a paper on the mineral apatite unveiled that when it grows at reduced conditions, meaning there is little or no free oxygen for chemical reactions, its sulphur would show a very specific signature. However, if it crystalised in oxidised conditions, the sulphur inside the apatite would look very different. This means that apatite is a proxy for redox conditions," explains Hugo Moreira, a CNRS postdoctoral researcher at the University of Montpellier and first author of the paper.

Moreira and colleagues decided to explore inclusions of phosphate-mineral apatite in zircon grains that are crystallized in magmas formed in an ancient subduction zone, and measured their sulphur valence speciation using X-ray absorption near edge structure (XANES) at the ESRF, the brightest synchrotron light source.

Sulphur incorporation and speciation in apatite is intrinsically dependent on the oxygen fugacity of the magma and therefore ideal for assessing the oxidation state during the evolution of magmatic systems. "Using apatite inclusions in zircons rather than apatite from the rock matrix was paramount, as the inclusions have been shielded by the extremely robust zircon crystals, preserving their original composition," explains Moreira.

The experiment results show that apatite inclusions in zircons from magmas that crystallised prior to the Great Oxidation Event have a relatively reduced sulphur redox state, whereas after the Great Oxidation Event they are more oxidised. The analysis on zircon shows that these magmas shared a similar source and that the younger samples had incorporated a sediment component. Overall, the clear implication is that sediments affected by an increasingly oxidised atmosphere modified the mantle and shifted the fugacity of magmas towards more oxidised conditions.

"Our study shows that investigating apatite inclusions in zircon using synchrotron X-rays is a powerful tool to constraint a critical magma parameter," concludes Moreira.

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