A special form of light made using an ancient Namibian gemstone could be the key to new light-based quantum computers, which could solve long-held scientific mysteries, according to new research led by the University of St Andrews.
The research, conducted in collaboration with scientists at Harvard University in the US, Macquarie University in Australia and Aarhus University in Denmark and published in Nature Materials, used a naturally mined cuprous oxide (Cu2O) gemstone from Namibia to produce Rydberg polaritons, the largest hybrid particles of light and matter ever created.
Rydberg polaritons switch continually from light to matter and back again. In Rydberg polaritons, light and matter are like two sides of a coin, and the matter side is what makes polaritons interact with each other.
This interaction is crucial because this is what allows the creation of quantum simulators, a special type of quantum computer, where information is stored in quantum bits. These quantum bits, unlike the binary bits in classical computers that can only be 0 or 1, can take any value between 0 and 1. They can therefore store much more information and perform several processes simultaneously.
This capability could allow quantum simulators to solve important mysteries of physics, chemistry and biology, for example, how to make high-temperature superconductors for highspeed trains, how cheaper fertilizers could be made potentially solving global hunger, or how proteins fold making it easier to produce more effective drugs.
Project lead Dr. Hamid Ohadi, of the School of Physics and Astronomy at the University of St Andrews, says that “making a quantum simulator with light is the holy grail of science. We have taken a huge leap towards this by creating Rydberg polaritons, the key ingredient of it.”
To create Rydberg polaritons, the researchers trapped light between two highly reflective mirrors. A cuprous oxide crystal from a stone mined in Namibia was then thinned and polished to a 30-micrometer thick slab (thinner than a strand of human hair) and sandwiched between the two mirrors to make Rydberg polaritons 100 times larger than ever demonstrated before.
One of the leading authors Dr. Sai Kiran Rajendran, of the School of Physics and Astronomy at the University of St Andrews, says that “purchasing the stone on eBay was easy. The challenge was to make Rydberg polaritons that exist in an extremely narrow color range.”
The team is currently further refining these methods in order to explore the possibility of making quantum circuits, which are the next ingredient for quantum simulators.
More information: Konstantinos Orfanakis et al, Rydberg exciton–polaritons in a Cu2O microcavity, Nature Materials (2022). DOI: 10.1038/s41563-022-01230-4 Provided by University of St Andrews.
An international team of climate scientists is working in North Canterbury to try to understand the reasons why giant glaciers disappeared thousands of years ago.
Massive pre-historic glaciers once stood on the banks of Lake Tennyson, North Canterbury. But they no longer exist today.
As glaciers retreat, they leave behind clues to their age in the form of sediment and boulders dropped by the ice as it melts. Called moraines, these piles of debris give us critical insights into Aotearoa New Zealand’s climate history.
Researchers from NIWA, Victoria University of Wellington, University of Maine, Lincoln University and GNS Science are studying the moraines around Lake Tennyson to work out why and when the glaciers disappeared.
Climate scientist Dr. Andrew Lorrey is leading the work for NIWA. “We need to understand the changes that we see in this landscape that happened millennia ago, because from the chronologies that are emerging, it looks like this landscape changed really, really fast.”
The work involves a combination of mapping with drones and LIDAR linked with cosmogenic isotope dating of boulders. This effort builds a picture of landscape evolution and shows when the glaciers were present and how they retreated over millennia.
Dr. Lorrey says understanding how and when the landscape changed in the past gives us important clues to what to expect in the future.
“We’re hopeful that we’ll be able to date those glacial landforms. We take a sample of a boulder that was dropped off by the ice in a moraine, do the chemistry on it and it tells us how long that boulder has been exposed to the atmosphere. We’ve got to understand that rapid change—and add to that what we understand about anthropogenic greenhouse gas emissions and what that does to the physical climate system. Put those two things together, you’ll have a stronger understanding of where we’re going in the future. “
With the climate crisis continuing to tighten its grip, nations around the world are making efforts to reduce emissions of climate warming gases. To track action, countries report their greenhouse gas emissions to the UNFCCC—the body responsible for driving global action to combat climate change.
While accurate and consistent reporting is crucial, very few countries exploit Earth observation satellite data to check and improve their estimates. Scientists have now devised new ways of comparing national greenhouse gas inventories with independent measurements taken from space.
Reducing emissions of greenhouse gases, such as carbon dioxide and methane, is clearly paramount to avoiding the worst impacts of climate change. But to understand if mitigation strategies are actually meeting reduction targets, accurate measurements of emissions are key.
Countries use estimates of sector-based activity to compile their national greenhouse gas reports and to show progress towards delivering on their carbon reduction commitments under the Paris Climate Agreement. Registries of greenhouse gas emissions, as well as the flux of carbon dioxide between the atmosphere and the ground over managed land, are based on national statistics following IPCC guidelines.
New research, published in Earth System Science Data, describes how scientists working within the Regional Carbon Assessment and Processes (RECCAP-2) project, supported by ESA, combined satellite measurements of atmospheric carbon dioxide and methane, and in-situ measurements of nitrous oxide, with a model that factors in the movement or “flux” of these greenhouse gases between the land surface and atmosphere.
This “inversion method” allowed the authors to determine emissions to the atmosphere of three greenhouse gases for a selection of high-emitting countries, as well as the overall flux of carbon dioxide over managed land. The managed land flux accounts for the absorption of carbon dioxide from the atmosphere due to the growth of crops and trees, their export and import across borders, and the anthropogenic component of rivers carrying carbon across borders, as well as carbon dioxide emissions from managed land owing to fires and other disturbances.
Gulf states: Saudi Arabia, Iraq, Kuwait, Oman, United Arab Emirates, Bahrain, Qatar Credit: Chart: ESA Source: Deng et al. 2021
Significant discrepancies between these inversion values and the corresponding national reports were found.
Methane emissions were found to be higher using the inversion method compared to most national reports. In particular, emissions from oil and gas extracting states in Central Asia and the Gulf were several times higher than officially reported.
The interactive graph above shows these discrepancies for the Gulf states between 2000 and 2016.
Absorbing 1.4 billion tons of carbon per year, the observed size of the global land carbon sink comprising ecosystems in both managed and unmanaged land, was several times larger than the 0.3 billion tons of carbon per year obtained by summing up countries’ reports.
Underreporting of this carbon sink was most evident for temperate and northern hemisphere countries, such as Canada and across the European Union.
Carbon dioxide absorbed by the land is counted negatively, while carbon dioxide emitted to the atmosphere is counted positively. Credit: Chart: ESA Source: Deng et al. 2021
In part, the disparity is explained by the carbon stored by unmanaged ecosystems that fall outside the inventory reporting protocol, while the full picture is observable from space.
The interactive graph below shows these discrepancies for Canada between 1990 and 2019.
With global temperatures having already risen by 1.1°C relative to pre-industrial levels, it is critical that policymakers have an accurate picture of emissions at both national and global scale.
Current guidelines used to compile national greenhouse gas inventories have their limitations. For example, they are usually based on scaled-up, sector-specific activity and rigid emission factors. Therefore, major emission sources, such as those from unmanaged land, fall out of scope. And, importantly, countries are only encouraged, but not required, to verify inventories against independently observed measurements.
In contrast, the new inversion method harnesses satellite data and in-situ observations to give a full picture of emissions that accumulate in the atmosphere.
Unlike national reporting guidelines, the inversion method captures seasonal and interannual extremes, such as drought and major wildfires, which are expected to increase in both frequency and severity as global temperatures ratchet upwards.
Philippe Ciais, from the Université Paris-Saclay, said, “The proposed method of using atmospheric inversions paves the way for countries and the global community to improve checks and consistency of national inventories to more accurately reflect global emissions.
“If regularly applied, this will not only improve transparency in the accounting process but will also improve the effectiveness of mitigation policy and progress by individual countries to meet their pledges as part of the Paris Climate Agreement.”
New satellite missions launched in the coming years will provide a much denser sampling of atmospheric carbon dioxide and methane. ESA is currently developing the Copernicus Anthropogenic Carbon Dioxide mission, which will be the first to measure how much carbon dioxide is released into the atmosphere specifically through human activity. The mission will provide the European Union with a unique and independent source of information to assess the effectiveness of policy measures, and to track their impact towards decarbonizing Europe and meeting national emission reduction targets.
More information: Zhu Deng et al, Comparing national greenhouse gas budgets reported in UNFCCC inventories against atmospheric inversions, Earth System Science Data (2022). DOI: 10.5194/essd-14-1639-2022 Provided by European Space Agency.
A celestial event mentioned in an ancient Chinese text turns out to be the oldest known reference to a candidate aurora, predating the next oldest one by some three centuries, according to a recent study by Marinus Anthony van der Sluijs, an independent researcher based in Canada, and Hisashi Hayakawa from Nagoya University. This finding was recently published in the journal Advances in Space Research.
The Bamboo Annals, or Zhushu Jinian in Mandarin, chronicle the history of China from the earliest legendary time to the time of their probable composition, in the 4th century BCE. Historical events aside, unusual observations in the sky make an occasional appearance in the text. Although this chronicle has been known to scholars for a long time, a fresh look at such old texts sometimes yields surprising new insights.
In this case, the authors examined the mention of a “five-colored light” seen in the northern part of the sky on a night towards the end of the reign of king Zhao of the Zhou dynasty. While the exact year is uncertain, they used up-to-date reconstructions of Chinese chronology to settle on 977 and 957 BCE as the two most likely years, depending on how Zhao’s reign is dated.
They found the record of the “five-colored light” to be consistent with a large geomagnetic storm. When the mid-latitude aurora is sufficiently bright, it can present a spectacle of multiple colors. The researchers cite several examples of this from historical records much closer to our time. The earth’s north magnetic pole is known to have been inclined to the Eurasian side in the mid-10th century BCE, about 15° closer to central China than at present. Therefore, the auroral oval could have been visible to observers in central China at times of significant magnetic disturbance. The study estimates that the equatorward boundary of the auroral oval would have been located at a magnetic latitude of 40° or less on the occasion.
This would be the earliest datable record of an aurora known from anywhere in the world. The finding comes barely two years after that of the previous holder of this distinction—several records of candidate aurorae inscribed on cuneiform tablets by Assyrian astronomers in the period 679–655 BCE. Some scientists have also associated Ezekiel’s vision, which is now dated to 594 or 593 BCE, with auroral visibility in the Middle East, but caveat must be noted for its reliability. Otherwise, another datable record of an early candidate aurora has been found for 567 BCE in the astronomical diary of the Babylonian king Nebuchadnezzar II.
Why did it take so long for scientists to recognize the aurora in the five-colored light of this chronicle entry? One reason is that the Bamboo Annals had a checkered history. The original manuscript was lost, rediscovered in the 3rd century CE and lost again during the Song dynasty. In the 16th century, a variant text was printed in which the object in the sky was not a five-colored light, but a comet. Now the new study shows that this cannot have been the original reading.
It is interesting in itself that popular descriptions of the northern lights can be pushed this far back in time. Such historical information is valuable for other reasons as well, however. It helps scientists to model long-term patterns in space weather variability and solar activity, on timescales from decades to millennia. Understanding these fluctuations can, in turn, help societies prepare for future solar eruptions of great magnitude and the disruption of technological infrastructure that they may cause. This record is now the only known historical reference to a space weather event before the Homeric Grand (Solar) Minimum (810–740 BCE), which should preferably be called the Neo-Assyrian Grand Minimum owing to Homer’s controversial historicity and dates.
More information: Marinus Anthony van der Sluijs et al, A candidate auroral report in the Bamboo Annals, indicating a possible extreme space weather event in the early 10th century BCE, Advances in Space Research (2022). DOI: 10.1016/j.asr.2022.01.010 Provided by Nagoya University.
In early September 2020, severe winds, high heat, and prolonged drought conditions led to the explosive growth of wildfires along the western slopes of the Cascades Mountains in the Pacific Northwest. The fires engulfed enormous tracts of forestland, destroyed communities, took dozen of lives, and cost hundreds of millions to fight.
In a first-of-its-kind study examining burn patterns from the 2020 Labor Day fires, researchers at Portland State University studied the influence of weather, topography, vegetation and other factors on burn severity in areas where the fires killed more than 75% of the trees. Their research confirms that extreme winds over the Labor Day holiday were the primary driver of the destructive force of the fires yet demonstrates how forest vegetation structure (e.g., canopy height, the age of trees, etc.) and topography played a significant role in burn severity patterns.
The paper, “Extreme Winds Alter Influence of Fuels and Topography on Megafire Burn Severity in Seasonal Temperate Rainforests under Record Fuel Aridity,” was recently published in the journal Fire.
According to the study’s co-author, Andrés Holz, associate professor of geography at Portland State, the wet temperate forests of the Cascade Mountains in the Pacific Northwest have a history of experiencing megafires of the scale of those that burned in 2020, but none had occurred since the early twentieth century. Because the scope and scale of the burns were unprecedented in modern times, they provided the research team a unique opportunity to gain a better understanding of the factors that influence the high severity of burns in these rainforests, including those on the western slopes of the Cascades. That understanding can inform planning for future land-use management in forestlands and the social and ecological impacts of extreme fire events in the context of a warming planet.
The research team developed maps for the extent and burn severity for five megafires and examined fire activity over two time periods: September 7-9, 2020, during which extreme winds fueled the explosive growth of the fires, and September 10-17, 2020, during which the fires continued burning under calm wind conditions. They then examined how the forest structure and topography influenced high-burn severity patterns, whether winds affected the relationship between those factors, and how high burn severity was affected by land management practices associated with land ownership.
“90% of the burning occurred during high winds,” said Dr. Cody Every, a Research Associate in the Department of Environmental Science and Management at Portland State and the study’s lead author. “But we also found that vegetation structure and canopy height were significant in determining where the fire burned more severely.”
The research team found that areas with younger trees and low canopy height and cover were particularly susceptible to high mortality rates. As Holz pointed out, this finding is of particular consequence to lumber production in the state, where trees grown on plantations are typically younger, uniformly spaced and located near communities and critical infrastructure.
Drawing on the historical record, the team, which included Portland State researchers Dr. Sebastian Busby and Associate Professor Max Nielsen-Pincus, also suggests that wildfire managers should anticipate re-burns in some areas affected by the 2020 megafires. Recently burned forests typically have higher flammability than unburned areas until the younger forest canopy closes again and finer fuels are shaded.
Given the composition of the temperate rainforests of the western slopes of the Cascade Mountains, where fuel proliferates, and the relationships between factors that contribute to megafires, the research team suggests that treatments such as prescribed fires and fuel reduction are not a practical approach to preventing future conflagrations. Instead, the team argues that we should focus on promoting resilient forests, increasing community preparedness, early suppression response, and hardening infrastructure.
More information: Cody Evers et al, Extreme Winds Alter Influence of Fuels and Topography on Megafire Burn Severity in Seasonal Temperate Rainforests under Record Fuel Aridity, Fire (2022). DOI: 10.3390/fire5020041 Provided by Portland State University.
Like Plato’s Cave, where fires reveal the portrait of an otherwise hidden reality, researchers have for the first time used a stalagmite’s chemical signal to reveal the nature of Australia’s historic wildfires, identifying differences before and after European settlement.
“For around 50 years, researchers have focused on the climate record contained in cave stalagmites,” says Prof Andy Baker, project chief investigator from UNSW’s School of Biological, Earth and Environmental Sciences. “However, hiding in the shadows all along was this geochemical record of past fires.”
The stalagmite used in the study, findings of which are published in the journal Geochimica et Cosmochimica Acta, was extracted from Yonderup cave in Western Australia and preserved a record of fires, climate conditions and the intervening years since its formation, allowing researchers to link local fires with any climatic antecedents.
“We found that the largest fire event in the [stalagmite] record, in approximately 1897, coincided with a decades-long drought period known as the Australian Federation drought,” says Dr. Liza McDonough from ANSTO and lead author of the study, conducted with UNSW and other universities. “The intensity of this fire was likely caused, at least partially, by these dry conditions.
Yanchep National Park after a fire in 2019. Credit: Andy Baker
“We also know that this [the largest fire] occurred a few decades after Indigenous cultural burning would have been suppressed by Europeans, so the fire was also probably exacerbated by a build-up of understory vegetation and dry combustible material on the forest floor due to removal of Indigenous land management practices.”
The researchers interpret the pre-European period captured in the stalagmite record as characterized by regular, low-intensity fires, while its post-European record depicts infrequent, high-intensity fires, which they speculate could be due to management practices.
This is the first study in which a stalagmite’s geochemistry has been used to describe historical fires. The technique relies upon the stalagmite’s composition, the variation in its elements and the order in which they were laid down.
“Nutrients such as phosphorus, and trace metals are found in bushfire ash and, in theory, can dissolve into waters that eventually infiltrate underground caves. Our research provides the first evidence that water containing high concentrations of these dissolved ash-derived elements can also alter the chemistry of a stalagmite and result in the preservation of signals from past fire events,” says Dr. McDonough.
Conceptual figure showing the impacts of extreme fire on the study’s stalagmite specimen. Credit: Geochimica et Cosmochimica Acta (2022). DOI: 10.1016/j.gca.2022.03.020
Why had stalagmites not been previously discovered as archives of past fires? “We realized we needed to use the highest resolution geochemical techniques available, as stalagmites grow very slowly. In one year, a stalagmite increases in height by the same thickness as that of a sheet of paper. The geochemical trace left by a fire would be even thinner.”
It’s not just historical fires that are recorded in stalagmites but also the annual accumulation of years, much like tree rings.
“In regions with high seasonality,” Dr. McDonough says, describing the stalagmite’s record of time, “wet winters can lead to a flush of organic matter into the dripwaters that form stalagmites. This causes annual dark bands alternating with light calcite bands in summer. This means that these stalagmites can be easily and precisely dated by counting back the annual layers.”
While the particular portion of stalagmite used in this study is relatively young, allowing scientists to peer back just 260 years, the range of time promised by other stalagmites and other speleothems (cave ornaments) stretches back much further, thousands or even tens of thousands of years.
This new technique opens the possibility of speleothems, and their chemical record, to describe historical fire and climatic events around the world “potentially anywhere we might find caves.” Pictured: Speleothems in Yonderup Cave, Yanchep National Park. Credit: Andy Baker
Dr. McDonough says the technique also grants new perspectives on climate change. “Speleothems record increasing or decreasing rainfall rates and changes in evaporation and their potential influence on local fire events, whether they’re becoming more or less frequent through time.
“Further investigation of the combined climate and fire records captured in stalagmites will allow us to understand the climatic conditions required for large bushfires to occur, which is essential to properly prepare for and mitigate the impacts of large fire events.”
The authors would like to respectfully acknowledge the Whadjuk Noongar people, the traditional custodians of the land at Yanchep where this study was conducted, for whom the land has strong mythological, ritual and ceremonial significance.
More information: Liza K. McDonough et al, Past fires and post-fire impacts reconstructed from a southwest Australian stalagmite, Geochimica et Cosmochimica Acta (2022). DOI: 10.1016/j.gca.2022.03.020 Journal information: Geochimica et Cosmochimica Acta Provided by University of New South Wales.
A new global analysis of the last 19 million years of seafloor spreading rates found they have been slowing down. Geologists want to know why the seafloor is getting sluggish.
New oceanic crust forms continuously along rifts thousands of miles long on the seafloor, driven by plate tectonics. As subduction pulls old crust down, rifts open up like fissures in an effusive volcano, drawing hot crust toward the surface. Once at the surface, the crust begins to cool and gets pushed away from the rift, replaced by hotter, younger crust.
This cycle is called seafloor spreading, and its rate shapes many global processes, including sea level and the carbon cycle. Faster rates tend to cause more volcanic activity, which releases greenhouse gases, so deciphering spreading rates helps contextualize long-term changes in the atmosphere.
Today, spreading rates top out around 140 millimeters per year, but peaked around 200 millimeters per year just 15 million years ago in some places, according to the new study. The study was published in the AGU journal Geophysical Research Letters, which publishes high-impact, short-format reports with immediate implications spanning all Earth and space sciences.
The slowdown is a global average, the result of varying spreading rates from ridge to ridge. The study examined 18 ridges, but took a particularly close look at the eastern Pacific, home to some of the globe’s fastest spreading ridges. Because these slowed greatly, some by nearly 100 millimeters per year slower compared to 19 million years ago, they dragged down the world’s average spreading rates.
It’s a complex problem to solve, made more difficult by the seafloor’s slow and steady self-destruction.
“We know more about the surfaces of some other planets than we do our own seafloor,” said Colleen Dalton, a geophysicist at Brown University who led the new study. “One of the challenges is the lack of perfect preservation. The seafloor is destroyed, so we’re left with an incomplete record.”
The seafloor is destroyed in subduction zones, where oceanic crust slides under continents and sinks back into the mantle, and is reforged at seafloor spreading ridges. This cycle of creation and destruction takes about every 180 million years, the age of the oldest seafloor. The crust’s magnetic record tracks this pattern, producing identifiable strips every time the Earth’s magnetic field reverses.
Dalton and her co-authors studied magnetic records for 18 of the world’s largest spreading ridges, using seafloor ages and their areas to calculate how much ocean crust each ridge has produced over the last 19 million years. Each ridge evolved a little differently: some lengthened, some shrank; some sped up, but almost all slowed down. The overall result of Dalton’s work is that average seafloor spreading slowed down by as much as 40% over that time.
The driver here might be located at subduction zones rather than spreading ridges: for example, as the Andes grow along the western edge of the South American continent, the mountains push down on the crust.
“Think of it as increased friction between the two colliding tectonic plates,” Dalton said. “A slowdown in convergence there could ultimately cause a slowdown in spreading at nearby ridges.” A similar process could have operated underneath the Himalaya, with the rapidly growing range slowing spreading along the ridges in the Indian Ocean.
However, Dalton points out, this added friction can’t be the only driver of the slowdown, because she found slowing rates globally and mountain growth is regional. Larger-scale processes, like changes in mantle convection, could also be playing a role. In all likelihood, she concludes, it’s a combination of both. To learn more, Dalton hopes to collect absolute plate speeds, rather than the relative speeds used in this study, which will better allow her to determine the cause of the slowdown.
More information: Colleen A. Dalton et al, Evidence for a Global Slowdown in Seafloor Spreading Since 15 Ma, Geophysical Research Letters (2022). DOI: 10.1029/2022GL097937 Journal information: Geophysical Research Letters Provided by American Geophysical Union.
If there was ever any doubt the 2011 discovery by a post-doctoral student was indeed the hottest rock on Earth, new findings from a Western-led research team are putting that uncertainty to rest.
Eleven years after researchers from Western unearthed what was then perceived as the hottest rock on Earth, a recent study found four additional zircon grains—a hard mineral commonly known as a substitute for diamonds—that confirmed the previous rock’s record-high temperature of 2,370 C.
The study, published in the journal Earth and Planetary Science Letters, was led by Earth sciences post-doctoral student Gavin Tolometti and co-authors: Timmons Erickson from NASA Johnson Space Center, Gordon Osinski and Catherine Neish from the department of Earth sciences; and Cayron Cyril from the Laboratory of Thermomechanical Metallurgy.
In 2011, then Ph.D. student Michael Zanetti was working with Osinski at the Mistastin Lake impact crater in Labrador when he found a glass rock that contained small zircon grains frozen inside it. That rock was later analyzed and found to have been formed at 2,370 C temperature as a result of an asteroid impact. These findings were shared in a study published in 2017.
In their own study using samples collected between 2009 and 2011, Tolometti and his colleagues were able to find four additional zircon grains that confirmed the 2011 discovery to be true. They researchers also located and found evidence in a different location within the same impact structure that the melt rock—rocks created after rock and soil melt into liquid after a meteor strikes—was differently superheated in more than one location, to a greater degree than previously theorized.
“The biggest implication is that we are getting a much better idea of how hot these impact melt rocks are, which initially formed when the meteorite struck the surface, and it gives us a much better idea of the history of the melt and how it cooled in this particular crater,” Tolometti said.
“It can also give us insight to study the temperature and melts in other impact craters.”
Tolometti also noted that most of the preserved evidence, such as glass samples and impact melt samples, were found close to the crater floor. By applying this knowledge to other impact craters, researchers might be able to find more evidence of the temperature conditions found in other craters but in less extensive studies.
“We’re starting to realize that if we’re wanting to find evidence of temperatures this high, we need to look at specific regions instead of randomly selecting across an entire crater,” he said.
Other discovery
The paper also noted this is the first time reidites—a mineral formed when zircon undergoes high pressure and temperatures—have been discovered at this site. The team found three reidites that were still preserved in the zircon grains, and evidence that another two were once present but had crystallized when temperatures had exceeded 1,200 C, at which point the reidite was no longer stable.
This mineral allows researchers to better constrain the pressure conditions indicating that there may have been a peak pressure condition around 30 to potentially above 40 gigapascals. These are the pressure conditions that were created when the meteorite struck the surface at that time. The closer something is to the impact event, the higher the pressure is going to be. Certain minerals that have been compressed greatly by this event—referred to as ‘shocked’—leave behind structures that can be studied.
“Considering how big the reidite was in our samples, we knew the minimum pressure it probably recorded was about 30 gigapascals. But since there is a lot of reidites still present within some of these grains, we know that it could even be above 40 gigapascals,” Tolometti explained.
This provides a better idea of the amount of pressure produced outside of the melting zone when the meteorite struck the surface. The melting zone will, by default, have pressures usually above 100 gigapascals, at which point a rock will completely melt or vaporize outside of those conditions.
Research expansion
The research group plans to expand this work to other impact craters on Earth. Some Ph.D. students will be working with Osinski to look at other craters such as Lac Wiyâshâkimî (Clearwater West crater) in Quebec. Tolometti is also looking to expand this work and look at Apollo lunar samples that were brought back to Earth, which have plenty of evidence to form from impact craters.
“If we were to find evidence of microstructures in zircon grains or other grains in pressure conditions, we could get a much better idea of what impact cratering processes are like on the moon,” he said.
“It can be a step forward to try and understand how rocks have been modified by impact cratering across the entire solar system. This data can then be applied into impact models to improve the results that we get.”
More information: G.D. Tolometti et al, Hot rocks: Constraining the thermal conditions of the Mistastin Lake impact melt deposits using zircon grain microstructures, Earth and Planetary Science Letters (2022). DOI: 10.1016/j.epsl.2022.117523 Nicholas E. Timms et al, Cubic zirconia in >2370 °C impact melt records Earth’s hottest crust, Earth and Planetary Science Letters (2017). DOI: 10.1016/j.epsl.2017.08.012
Journal information: Earth and Planetary Science Letters.
Mesozoic granitoids, ranging from the Triassic to the Cretaceous, are widely distributed in Qinling orogen. They provide excellent clues for understanding the crustal evolution and geodynamic evolution of the orogenic belt.
Recently, a research team led by Prof. Sun Weidong from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) and Prof. Chen Fukun from University of Science and Technology of China (USTC) provided a data set comprising zircon Uranium-Lead (U-Pb) dating and elemental and Strontium-Neodymium (Sr-Nd) isotopic geochemistry for Late Mesozoic granite and microgranular enclaves (MME) exposed in the Taibai complex pluton.
The study was published in the Journal of Earth Science.
The researchers found that the granite and MME yielded concordant U-Pb zircon ages of 124 Ma to 118 Ma, indicating roughly simultaneous magmatism in the Late Mesozoic.
The granite rocks were characterized by enrichment in large ion lithophile elements, depletion in high field strength elements, and variable Sr/Y ratios of 7.64 to 63.6. “Low MgO, Cr, and Ni contents imply that the magmas were essentially crustal-derived,” said Xue Yingyu, first author of the study.
They also found that both the granite and the MME showed relative depletion in Sr-Nd isotopic composition, suggesting that the magma(s) originated from juvenile crustal rocks. These Sr-Nd isotopic characteristics were significantly different from those of other Late Mesozoic granitoids exposed elsewhere in the Qinling orogenic belt, which formed from much older and enriched sources and with negligible contributions from mantle or juvenile crust.
“We proposed a reworking event of the juvenile crust during the Late Mesozoic that was triggered by the tectonic extension and subsequent asthenospheric upwelling that occurred in eastern China,” said Prof. Sun.
More information: Ying-Yu Xue et al, Reworking of the Juvenile Crust in the Late Mesozoic in North Qinling, Central China, Journal of Earth Science (2022). DOI: 10.1007/s12583-021-1521-0 Provided by Chinese Academy of Sciences.
How are fluvial valleys formed? Why do rivers cut valleys? Which mechanisms control the rate of fluvial incision? These are universal questions in Geomorphology about river erosion, and researchers from the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH) have addressed them through a comprehensive study centering on the upper course of the Ebro River where it runs through the zones of the Tobalina valley, Miranda depression, and Haro sector, which belong to the provinces of Burgos, Álava, and La Rioja.
The results of this study, published in the journal Global and Planetary Change, make clear that vertical erosion by the Upper Ebro is declining and could eventually stop, when the valley would no longer deepen.
It is seen all over the world that many rivers have formed ever deeper and narrower entrenched valleys in their most recent phases of evolution: examples are the Yellow River in China, the Colorado canyon in North America, and rivers like the Seine, Rhine, Thames, and Ebro, in Europe.
A variety of studies have linked this generalized phase of valley entrenchment with a global event of stronger incision by rivers that started 700,000–1,200,000 years ago, up to the present day.
This rise in fluvial erosion has been explained by tectonic uplift which would have occurred in different parts of the planet generally, as well as by a harsher climate, as from that moment, more extreme and longer climatic cycles (100,000 years) became established, whose effects on vegetation cover and water flow would have stimulated erosion.
Nevertheless, this study of the surprising sequence identified in the Upper Ebro valley has furnished a record of something completely different. In the zones looked at, no fewer than 22 ancient terrace levels, namely, fluvial terraces indicating how valleys evolved, have been identified, and their position and dating reveal a gradual fall in the rate of bedrock erosion.
“These results show that the Upper Ebro has been losing incision strength for the last 1.2 million years, and it may stop deepening its valley in the near future, reaching what is known as a steady state,” according to Alfonso Benito Calvo, lead author of the study.
The data suggest that the zone of the Cantabrian Mountains through which the Upper Ebro runs is tectonically stable, and that the Quaternary climatic changes have been unable to rekindle the incision capacity of this river, in contrast with the middle and lower sections of the basin, where fewer fluvial levels are conserved but these suggest a higher incision rate.
More information: Alfonso Benito-Calvo et al, Towards the steady state? A long-term river incision deceleration pattern during pleistocene entrenchment (Upper Ebro River, Northern Spain), Global and Planetary Change (2022). DOI: 10.1016/j.gloplacha.2022.103813 Journal information: Geomorphology Provided by CENIEH.
