“It is the perfect sample to close a 2-billion-year gap,” said Brad Jolliff, the Scott Rudolph Professor of Earth and Planetary Sciences in Arts & Sciences and director of the university’s McDonnell Center for the Space Sciences. Jolliff is a U.S.-based co-author of an analysis of the new moon rocks led by the Chinese Academy of Geological Sciences, published Oct. 7 in the journal Science.

The age determination is among the first scientific results reported from the successful Chang’e-5 mission, which was designed to collect and return to Earth rocks from some of the youngest volcanic surfaces on the moon.

“Of course, ‘young’ is relative,” Jolliff said. “All of the volcanic rocks collected by Apollo were older than 3 billion years. And all of the young impact craters whose ages have been determined from the analysis of samples are younger than 1 billion years. So the Chang’e-5 samples fill a critical gap.”

The gap that Jolliff references is important not only for studying the moon, but also for studying other rocky planets in the solar system.

As a planetary body, the moon itself is about 4.5 billion years old, almost as old as the Earth. But unlike the Earth, the moon doesn’t have the erosive or mountain-building processes that tend to erase craters over the years. Scientists have taken advantage of the moon’s enduring craters to develop methods of estimating the ages of different regions on its surface, based in part on how pocked by craters the area appears to be.

This study shows that the moon rocks returned by Chang’e-5 are only about 2 billion years old. Knowing the age of these rocks with certainty, scientists are now able to more accurately calibrate their important chronology tools, Jolliff said.

“Planetary scientists know that the more craters on a surface, the older it is; the fewer craters, the younger the surface. That’s a nice relative determination,” Jolliff said. “But to put absolute age dates on that, one has to have samples from those surfaces.”

“The Apollo samples gave us a number of surfaces that we were able to date and correlate with crater densities,” Jolliff explained. “This cratering chronology has been extended to other planets — for example, for Mercury and Mars — to say that surfaces with a certain density of craters have a certain age.”

“In this study, we got a very precise age right around 2 billion years, plus or minus 50 million years,” Jolliff said. “It’s a phenomenal result. In terms of planetary time, that’s a very precise determination. And that’s good enough to distinguish between the different formulations of the chronology.”

Other interesting findings from the study relate to the composition of basalts in the returned samples and what that means for the moon’s volcanic history, Jolliff noted.

The results presented in the Science paper are just the tip of the iceberg, so to speak. Jolliff and colleagues are now sifting through the regolith samples for keys to other significant lunar science issues, such as finding bits and pieces tossed into the Chang’e 5 collection site from distant, young impact craters such as Aristarchus, to possibly determining the ages of these small rocks and the nature of the materials at those other impact sites.

Jolliff has worked with the scientists at the Sensitive High Resolution Ion MicroProbe (SHRIMP) Center in Beijing that led this study, including study co-author Dunyi Liu, for over 15 years. This long-term relationship is possible through a special collaboration agreement that includes Washington University and its Department of Earth and Planetary Sciences, and Shandong University in Weihai, China, with support from Washington University’s McDonnell Center for the Space Sciences.

“The lab in Beijing where the new analyses were done is among the best in the world, and they did a phenomenal job in characterizing and analyzing the volcanic rock samples,” Jolliff said.

“The consortium includes members from China, Australia, the U.S., the U.K. and Sweden,” Jolliff continued. “This is science done in the ideal way: an international collaboration, with free sharing of data and knowledge — and all done in the most collegial way possible. This is diplomacy by science.”

Jolliff is a specialist in mineralogy and provided his expertise for this study of the Chang’e-5 samples. His personal research background is focused on the moon and Mars, the materials that make up their surfaces and what they tell about the planets’ history.

As a member of the Lunar Reconnaissance Orbiter Camera science team and leader of the Washington University team in support of NASA’s Apollo Next Generation Sample Analysis (ANGSA) program, Jolliff investigates the surface of the moon, relating what can be seen from orbit to what is known about the moon through the study of lunar meteorites and Apollo samples — and now, from Chang’e-5 samples.

The images also reveal evidence that the crater endured flash floods. This flooding was energetic enough to sweep up large boulders from tens of miles upstream and deposit them into the lakebed, where the massive rocks lie today.

The new analysis, published today in the journal Science, is based on images of the outcropping rocks inside the crater on its western side. Satellites had previously shown that this outcrop, seen from above, resembled river deltas on Earth, where layers of sediment are deposited in the shape of a fan as the river feeds into a lake.

Perseverance’s new images, taken from inside the crater, confirm that this outcrop was indeed a river delta. Based on the sedimentary layers in the outcrop, it appears that the river delta fed into a lake that was calm for much of its existence, until a dramatic shift in climate triggered episodic flooding at or toward the end of the lake’s history.

“If you look at these images, you’re basically staring at this epic desert landscape. It’s the most forlorn place you could ever visit,” says Benjamin Weiss, professor of planetary sciences in MIT’s Department of Earth, Atmospheric and Planetary Sciences and a member of the analysis team. “There’s not a drop of water anywhere, and yet, here we have evidence of a very different past. Something very profound happened in the planet’s history.”

As the rover explores the crater, scientists hope to uncover more clues to its climatic evolution. Now that they have confirmed the crater was once a lake environment, they believe its sediments could hold traces of ancient aqueous life. In its mission going forward, Perseverance will look for locations to collect and preserve sediments. These samples will eventually be returned to Earth, where scientists can probe them for Martian biosignatures.

“We now have the opportunity to look for fossils,” says team member Tanja Bosak, associate professor of geobiology at MIT. “It will take some time to get to the rocks that we really hope to sample for signs of life. So, it’s a marathon, with a lot of potential.”

Tilted beds

On Feb. 18, 2021, the Perseverance rover landed on the floor of Jezero crater, a little more than a mile away from its western fan-shaped outcrop. In the first three months, the vehicle remained stationary as NASA engineers performed remote checks of the rover’s many instruments.

During this time, two of Perseverance’s cameras, Mastcam-Z and the SuperCam Remote Micro-Imager (RMI), captured images of their surroundings, including long-distance photos of the outcrop’s edge and a formation known as Kodiak butte, a smaller outcop that planetary geologists surmise may have once been connected to the main fan-shaped outcrop but has since partially eroded.

Once the rover downlinked images to Earth, NASA’s Perseverance science team processed and combined the images, and were able to observe distinct beds of sediment along Kodiak butte in surprisingly high resolution. The researchers measured each layer’s thickness, slope, and lateral extent, finding that the sediment must have been deposited by flowing water into a lake, rather than by wind, sheet-like floods, or other geologic processes.

The rover also captured similar tilted sediment beds along the main outcrop. These images, together with those of Kodiak, confirm that the fan-shaped formation was indeed an ancient delta and that this delta fed into an ancient Martian lake.

“Without driving anywhere, the rover was able to solve one of the big unknowns, which was that this crater was once a lake,” Weiss says. “Until we actually landed there and confirmed it was a lake, it was always a question.”

Boulder flow

When the researchers took a closer look at images of the main outcrop, they noticed large boulders and cobbles embedded in the youngest, topmost layers of the delta. Some boulders measured as wide as 1 meter across, and were estimated to weigh up to several tons. These massive rocks, the team concluded, must have come from outside the crater, and was likely part of bedrock located on the crater rim or else 40 or more miles upstream.

Judging from their current location and dimensions, the team says the boulders were carried downstream and into the lakebed by a flash-flood that flowed up to 9 meters per second and moved up to 3,000 cubic meters of water per second.

“You need energetic flood conditions to carry rocks that big and heavy,” Weiss says. “It’s a special thing that may be indicative of a fundamental change in the local hydrology or perhaps the regional climate on Mars.”

Because the huge rocks lie in the upper layers of the delta, they represent the most recently deposited material. The boulders sit atop layers of older, much finer sediment. This stratification, the researchers say, indicates that for much of its existence, the ancient lake was filled by a gently flowing river. Fine sediments — and possibly organic material — drifted down the river, and settled into a gradual, sloping delta.

However, the crater later experienced sudden flash floods that deposited large boulders onto the delta. Once the lake dried up, and over billions of years wind eroded the landscape, leaving the crater we see today.

The cause of this climate turnaround is unknown, although Weiss says the delta’s boulders may hold some answers.

“The most surprising thing that’s come out of these images is the potential opportunity to catch the time when this crater transitioned from an Earth-like habitable environment, to this desolate landscape wasteland we see now,” he says. “These boulder beds may be records of this transition, and we haven’t seen this in other places on Mars.”

This research was supported, in part, by NASA.

Nitrogen dioxide is a common air pollutant that can cause a range of health problems, such as chronic respiratory illness and asthma. But it can be difficult to trace.

A new study used high-resolution air pollution data measured with satellites to track NO₂ for nearly two years in major cities across the U.S. The researchers then paired the pollution data with both demographic data and metrics that analyze the degree of racial segregation in a community.

Cities with bigger populations tended to have larger disparities in NO₂ pollution between low-income neighborhoods of color and high-income white neighborhoods, according to the study. Phoenix, Los Angeles and Newark, N.J., have the highest NO₂ inequalities, all with a discrepancy in NO₂ exposure of over 40%.

Both commuter traffic and heavy-duty trucks contribute NO₂ and other pollutants, but diesel trucks are the dominant source, contributing on average up to half of a city’s NO₂ despite being at most 5% of traffic. Because diesel trucks also emit other harmful gases and particulates, changes in NO₂ are also thought to reflect exposure to other pollutants as well.

The findings are detailed in the AGU journal Geophysical Research Letters, which publishes high-impact, short-format reports with immediate implications spanning all Earth and space sciences.

“One of the novel things we looked at was the integration of segregation metrics and air quality. Previously, we had been limited in our ability to address air pollution inequality, but with improvements in satellite resolution we are now able to get spatially and temporally continuous data at finer resolutions within cities,” said Angelique Demetillo, an atmospheric chemist at the University of Virginia and lead author of the study.

Measuring pollutants like NO₂ is difficult to do at a scale that’s useful to local policymakers. While previous studies have shown disparities in air quality, the new findings offer near-daily pollution data at small scales, providing important quantitative information policymakers can use to guide zoning and public health and that can reflect the lived experience of community members.

The new study found a 60% drop in heavy trucking on weekends results in a 40% decrease in air pollution inequality. That can point policymakers to a clear emissions-reducing target.

“In terms of environmental justice, one of the things we have lacked is these observations across an entire city that also have temporal variability that we can use to understand the sources [of pollution],” said Sally Pusede, an atmospheric chemist at the University of Virginia who co-authored the study.

“We have these new data and methodologies that continue to show us what we already know through experience, but in the U.S., it’s [quantitative] data that informs policy,” said Regan Patterson, a transportation and public health expert at the Congressional Black Caucus Foundation.

Bigger city, bigger disparity

Transitioning to electric heavy-duty trucks could be one way of reducing pollution exposure in neighborhoods close to highways. California already has a mandate of doing this by 2045. But, Pusede pointed out, while emissions from diesel trucks are the biggest driver of exposure inequality, other pollution sources contribute to the problem. “Even if we eliminated emissions from trucking, we would still see inequalities present because there are other sources of inequality.”

Discrepancies in exposure to pollution between communities of color and white communities are well-documented. They often stem from zoning practices that result in communities of color forming in less desirable areas or infrastructure like highways being built in close proximity to — or through — a neighborhood.

Patterson said over the long term, transformative changes are needed to truly begin to remove NO₂ pollution disparity. “How do you rectify the inequities that have literally been built into the environment, where certain groups are more likely to be adjacent to major roadways?” she asked.

Both Patterson and Pusede referenced a bill in the new infrastructure package aimed at physically reconnecting communities by removing freeways as a necessary step toward equalizing air quality. More immediately, Demetillo hoped her study and studies like it will help put air-quality information into the hands of community members.

“I see this as just the beginning. There are a lot of potential end-user applications, like people in different cities using this information to help them make decisions about how to go about their day. For policymakers, this could be a new way to plan mitigation solutions or to monitor how well those mitigation strategies are playing out,” Demetillo said.

Human activity and climate change are causing invasive non-native species to spread rapidly across the globe. Researchers have found that certain invasive species can push lake ecosystems beyond a critical ‘tipping point’, causing a sudden shift from healthy to degraded conditions that is difficult to reverse.

Invasive fish such as Asian silver carp Hypophthalmichthys molitrix, and crustaceans such as American signal crayfish Pacifastacus leniusculus, were found to significantly reduce the abundance of other important organisms in lakes and degrade water quality. The findings, published today in the journal Global Change Biology, also provide guidance on the best ways to manage waterbodies.

Shallow lakes naturally exist in one of two alternative stable states: either healthy — with clear water with an abundance of vegetation, or degraded — with cloudy water dominated by algae. When a lake is in the latter state, algae use up all the nutrients in the water and block sunlight, preventing the growth of aquatic vegetation that would aid ecosystem recovery.

Deteriorated, algae-dominated freshwater ecosystems also threaten the health and water security of human populations. Blooms of cyanobacteria, known as ‘blue-green algae’ can produce toxins that contaminate food webs and poison water supplies.

“Algal blooms represent one of the most significant threats to the security of the Earth’s surface freshwaters. Simply undoing the circumstances that triggered a tipping point will not restore the ecosystem — the road to recovery is slow and steep,” said Dr Sam Reynolds in the University of Cambridge’s Department of Zoology, first author of the report.

However, although invasive species are recognised as a significant threat to global biodiversity, their impacts on ecosystem services may not be uniformly negative. Invasive molluscs, including the zebra mussel Dreissena polymorpha, were found to engineer the opposite biological and environmental response: they delay ecosystem collapse and potentially aid the recovery of degraded lake ecosystems.

“Managers of drinking water reservoirs, for example, may be able to avoid the cost of dealing with blooms of harmful algae, by removing invasive crayfish but allowing established non-native zebra mussels to remain and act as biological filters,” said Professor David Aldridge, senior author of the report.

He added: “Early detection and rapid response plans should always be our first line of attack. But in situations where invaders have already established and can no longer be eradicated, it may be appropriate to embrace their positive effects.”

The researchers focused on shallow lake ecosystems, but say that their framework could be applied to other critical ecosystems that experience catastrophic tipping points — such as coral reefs, kelp forests and desert shrublands.

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In “The Effects of Air Pollution on Students’ Cognitive Performance: Evidence from Brazilian University Entrance Tests,” authors Juliana Carneiro, Matthew A. Cole, and Eric Strobl use Brazilian data on concentrations of ozone (O3) and particulate matter (PM10) and a data set of students’ scores to examine the impact of air pollution on academic performance in national examinations. The air pollution data focuses on Rio de Janeiro and São Paulo — Brazil’s most industrialized states — using air pollution and weather monitoring station data to build a unique data panel from 2015-17.

The authors constructed individual-level panel data for the two days of exams across three years and applied student fixed effects to address potential endogeneity concerns. “In addition,” they note, “We take advantage of plausibly exogenous spatial and temporal variation in PM10 across municipalities in the states of Rio de Janeiro and São Paulo and utilize an instrumental variable approach based on wind direction.”

The findings suggest that an increase of 10 micrograms per cubic meter (mg/m3) of PM10 on the day of the examination decreases students’ scores by 6.1 points (8% SD). “Even when including a more flexible measure of our treatment that is utilizing a dummy variable to account for the days in which PM10 exceeded the WHO’s acceptable threshold, our findings still point to negative effects of air pollution on cognitive performance during examinations,” they note. Placebo tests, sensitivity checks, and falsifications tests reinforced the main findings: evidence of a link between air pollution and exam performance.

Consistent with previous studies, the authors also find evidence that the effect of air pollution on exam performance appears to affect males more adversely than females. “Our results also suggest that poorer students may be more susceptible to air pollution than wealthier exam takers,” they write, adding, “Our findings provide plausible evidence to suggest that cognitive performance may be hindered by poor air quality, but unequally so.”

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The team from the University of Göttingen, Ludwig Maximilian University of Munich and the University of Texas (Dallas) used two-layer graphene in its natural form. The delicate graphene flakes are contacted using standard microfabrication techniques and the flake is positioned so that it is hangs freely like a bridge, held at the edges by two metal contacts. The extremely clean double-layers of graphene show a quantisation of electrical resistance at low temperatures and almost undetectable magnetic fields. In addition, the electrical current flows without any loss of energy. The reason for this is a form of magnetism that is not generated in the usual way as seen in conventional magnets (ie by the alignment of the intrinsic magnetic moments of electrons), but by the motion of the charged particles in the graphene double layer itself. “In other words, the particles generate their own intrinsic magnetic field, which leads to the quantisation of the electrical resistance,” says Professor Thomas Weitz from the University of Göttingen.

The reason this effect is special, is not just that it only requires an electric field, but also that it occurs in eight different versions that can be controlled by applied magnetic and electric fields. This results in a high degree of control, because the effect can be switched on and off and the direction of movement of the charged particles can be reversed. “This makes it a really interesting candidate for potential applications, for example, in the development of innovative computer components in the field of spintronics, which could have implications for data storage,” says Weitz. “In addition, it is an advantage that we can show this effect in a system comprising a simple and naturally occurring material. This is in stark contrast to the recently popularised ‘heterostructures’, which require a complex and precise composition of different materials.”

First, however, the effect must be further investigated and ways to stabilize it at higher temperatures need to be found, because currently it only occurs at up to five degrees above absolute zero (the latter being 273 degrees below 0^oC).”

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