Assistant professor Michael Maseda was one of many who contributed to development of the James Webb Space Telescope.
He looks forward to using the instrument to take “baby pictures of galaxies”—potentially looking as far back into the history of the universe as the Big Bang itself.
Provided by University of Wisconsin-Madison.
Astronomers have measured the icy heart of one of the largest comets ever discovered — a gargantuan, 4 billion-year-old rock that’s currently barreling toward Earth at 22,000 mph (35,000 km/h).
Don’t worry: The enormous, icy rock — named C/2014 UN271, or Bernardinelli-Bernstein (BB) after its discoverers — is on course to miss our planet by about 1 billion miles when it makes its closest approach in 2031, Live Science previously reported. For comparison, that’s greater than the average distance between Saturn and the sun — and far enough away that stargazers won’t be able to see BB’s flyby with the naked eye.
However, as BB zooms ever closer, astronomers are taking the opportunity to study it in ever greater detail. Previous research showed that the icy space rock measures more than 80 miles (128 km) across — about twice the width of Rhode Island — and is about 100 thousand times more massive than a typical comet. BB is so large that it was once mistaken for a dwarf planet; more recent observations showed that the rock sports a glowing tail, or coma, which is a clear indicator of an icy comet soaring through the relatively warm inner solar system.
Now, astronomers have used the Hubble Space Telescope to peer through the rock’s blazing coma and focus directly on its icy heart. While BB is still too far away to image in clear detail, the Hubble observations allowed researchers to identify a bright spot of light corresponding to the comet’s heart, or nucleus, according to research published April 12 in The Astrophysical Journal Letters.
The team then used a computer model to digitally remove the glow of the comet’s bright coma, leaving behind just the nucleus. The resulting data shows that the comet’s nucleus is about 50 times larger than typical comets observed in the inner solar system — the single largest nucleus astronomers have ever detected.
The team’s analysis also revealed the color of the comet’s icy nucleus.
“It’s big and it’s blacker than coal,” study co-author David Jewitt, a planetary science professor at UCLA, said in a statement.
Still roughly 2 billion miles (3.2 billion kilometers) from Earth, BB has plenty of space to cover before its close-up in 2031. Researchers reported in a study published in November 2021 in The Astrophysical Journal Letters that the comet made its last close approach to Earth 3.5 million years ago, when it came within about 1.6 billion miles (2.6 billion km) of the sun.
In the meantime, BB has been swooping through the Oort cloud — a vast scrapyard of icy rocks that encircles our solar system, potentially stretching for billions of miles into space.
Originally published on Live Science.
A magnetosphere forms around any magnetized object, such as a planet, that is immersed within a stream of ionized gas, called plasma. Because Earth possesses an intrinsic magnetic field, the planet is surrounded by a large magnetosphere that extends out into space, blocks lethal cosmic rays and particles from the sun and stars, and allows life itself to exist.
In Physics of Plasmas, scientists from Princeton, UCLA, and the Instituto Superior Técnico, Portugal, report a method to study smaller magnetospheres, sometimes just millimeters thick, in the laboratory.
These mini-magnetospheres have been observed around comets and near certain regions of the moon and have been suggested to propel spacecraft. They are good testbeds for studying larger planet-sized magnetospheres.
Previous laboratory experiments have been carried out utilizing plasma wind tunnels or high-energy lasers to create mini-magnetospheres. However, these earlier experiments were limited to 1D measurements of magnetic fields that do not capture the full 3D behavior scientists need to understand.
“To overcome these limitations, we have developed a new experimental platform to study mini-magnetospheres on the Large Plasma Device (LAPD) at UCLA,” said author Derek Schaeffer.
This platform combines the magnetic field of the LAPD with a fast laser-driven plasma and a current-driven dipole magnet.
The LAPD magnetic field provides a model of the solar system’s interplanetary magnetic field, while the laser-driven plasma models the solar wind and the dipole magnet provides a model for the Earth’s inherent magnetic field. Motorized probes allow system scans in three dimensions by combining data from tens of thousands of laser shots.
One advantage to using this setup is that the magnetic field and other parameters can be carefully varied and controlled.
If the dipole magnet is switched off, all signs of a magnetosphere disappear. When the magnetic field of the dipole is switched on, a magnetopause can be detected, which is key evidence of the formation of a magnetosphere.
A magnetopause is the place in the magnetosphere where pressure from the planetary magnetic field is exactly balanced by the solar wind. The experiments revealed that as the dipole magnetic field is increased, the magnetopause gets larger and stronger.
The effect on the magnetopause was predicted by computer simulations, which were carried out by the investigators to understand and validate their experimental results more fully. These simulations will also guide future experiments, including studies utilizing a cathode recently installed on the LAPD.
“The new cathode will enable faster plasma flows, which in turn will allow us to study the bow shocks observed around many planets,” Schaeffer said.
Other experiments will study magnetic reconnection, an important process in Earth’s magnetosphere in which magnetic fields annihilate to release tremendous energy.
More information: Laser-driven, ion-scale magnetospheres in laboratory plasmas. I. Experimental platform and first results, Physics of Plasmas (2022). aip.scitation.org/doi/full/10.1063/5.0084353
Journal information: Physics of Plasmas
Provided by American Institute of Physics.
The largest antenna ever tested in ESA’s Hertz radio frequency test chamber is this 5-m diameter transponder antenna, which will operate down on the ground to help calibrate the Biomass mission, which will chart all the forests on Earth.
“This is a particularly challenging test campaign both in terms of the size of the antenna and the very low P-band frequency that Biomass will be using, which allows it to pierce through forest canopies to acquire individual trees,” explains ESA antenna engineer Luis Rolo, overseeing the test campaign.
“Usually when we test a large satellite here, its antenna is significantly smaller, typically between 0.5 and 2 meters across. But this entire structure is a radiating antenna in its own right, its sides coming near to the chamber walls.
“What this means is that the testing process highlight some aspects of the chamber we’ve never seen before, even after many years of testing. But we’ve come up with a measurement method involving multiple acquisitions from different spots within the chamber, combined carefully to subtract such environmental effects, yielding very accurate results.”
Part of ESA’s technical heart in the Netherlands, the metal-walled “Hybrid European Radio Frequency and Antenna Test Zone” chamber is shut off from all external influences. Its internal walls are studded with radio-absorbing “anechoic” foam pyramids, allowing radio-frequency testing without any distorting reflections.
Its name starts with Hybrid because the chamber can assess radio signals from antennas both in localized “near-field” terms or else on a “far-field” basis, as if the signal has crossed thousands of kilometers of space.
Due to be launched next year, Biomass will deploy a massive 12-m diameter reflector to harness P-band radar signals in order to perform a five-year census of all Earth’s trees.
Based in Australia, this transponder will be integrated onto a mobile positioning system inside a protective radome, allowing it to track the Biomass satellite moving across the sky. The transponder antenna will reflect radar signals from Biomass back to it, to help confirm the mission is operating optimally. The transponder was developed and built by Italian company IDS.
Provided by European Space Agency.
When astronauts begin exploring Mars, they will face numerous challenges. Aside from the time and energy it takes to get there and all the health risks that come with long-duration missions in space, there are also the hazards of the Martian environment itself. These include Mars’ incredibly thin and toxic and toxic atmosphere, the high levels of radiation the planet is exposed to, and the fact that the surface is extremely cold and drier than the driest deserts on Earth.
As a result, missions to Mars will need to leverage local resources to provide all the basic necessities, a process known as In-Situ Resource Utilization (ISRU). Looking to address the need for propellant, a team from the Spanish innovation company Tekniker is developing a system that uses solar power to convert astronaut wastewater into fuel. This technology could be a game-changer for missions to deep space in the coming years, including the moon, Mars and beyond.
Headquartered in northeastern Spain, Tekniker is a non-profit research, development, and innovation (R&D&I) organization that specializes in advanced manufacturing and information and communications technology (ICT). This photoelectrochemical system relies on high-efficiency catalytic materials to produce hydrocarbons like methane, carbon monoxide, or alcohols from atmospheric CO2 and wastewater.
In the process, the system also detoxifies the wastewater used, operating as a water-recycling method. The system is the brainchild of Tekniker telecommunications engineer Dr. Borja Poza and material engineer Dr. Eva Gutierrez. As Poza explained in a recent ESA press release:
“We aim to make the first reactor to produce space propellant on Mars using the planet’s air, which is 95% carbon dioxide. The reactor will be powered by sunlight, and astronauts’ greywater will be used to help in the production of the propellant.”
On Mars, liquid water is not readily available, but multiple lines of evidence indicate that subsurface ice exists in many regions. In keeping with the ISRU process, future missions would harvest this ice to provide drinking water, irrigation for plants, sanitation, and manufacture rocket fuel. This is done by breaking down water molecules (H2O) to produce molecular hydrogen (H2) and oxygen gas (O2).
When cooled to cryogenic temperatures, these elements become the two ingredients of conventional hydrogen fuel—i.e., liquid hydrogen and liquid oxygen (LOX). Hence, the locations of water ice deposits on Mars are a major concern for mission planners and the selection of future landing sites. Around the poles, there are abundant supplies of water concentrated in the ice caps, and layers of subsurface permafrost have been observed at all latitudes.
In some spots around the poles, water ice has been detected just 30 cm (about 12 inches) beneath the surface, making it easily accessible. Recent data obtained by the ExoMars Trace Gas Orbiter (TGO) revealed large amounts of ice mixed with regolith at the bottom of Mars’ massive canyon system—Valles Marineris. There is also evidence that there may be underground sources of ice around the planet’s mid-latitudes, though this remains a contentious possibility.
Jean-Christophe Berton, the ESA technical officer for the project at the European Space Operations Center (ESOC) in Germany, said, “The outcome of this activity could provide ESA with valuable input on the production of propellant on Mars or to power remote sites like ground stations on Earth. It could also potentially provide input on how to decarbonize our own atmosphere.”
The project was submitted in response to an open call from the ESA’s Open Space Innovation Platform (OSIP), which seeks promising new ideas for applications in space. This system is one of many technologies that will allow astronauts and crews to live and work sustainably for extended periods on the moon, Mars, and beyond. In these environments, resupply missions will take weeks or months to reach them, making reliance on Earth impractical.
These include technologies that will allow astronauts to use local regolith to construct habitats that will protect against the elements and radiation on Mars, grow and cultivate food inside these habitats, and create oxygen gas from the Martian atmosphere.
Provided by Universe Today.
In a paper published today in Nature Communications, a team led by scientists from the University of California, Irvine, using climate models and satellite data, reveal for the first time how protecting tropical forests can yield climate benefits that enhance carbon storage in nearby areas.
Many climate scientists use computer simulations to mimic the planet’s climate as it exists today and how it may exist in the future as humanity keeps emitting greenhouse gases. Such models rely on accurate measurements all the moving parts of the climate system, from how much sunlight hits and warms the climate, to the response of forest biomass to changes in temperature, rainfall and atmospheric carbon dioxide levels.
The list of moving parts is long, and one part that has until now remained unmeasured is the degree to which deforestation in tropical rainforests like the Amazon and the Congo contributes to additional forest losses because of its effect on regional climate.
“We used Earth system models to quantify what the climate impact from tropical deforestation is today,” said lead author Yue Li, UCI postdoctoral researcher in Earth system science. “Then, we used this information with satellite observations of forest biomass to figure out how nearby forests are responding to these changes.”
Jim Randerson, UCI professor of Earth system science, added: “This paper shows that avoiding deforestation yields carbon benefits in nearby regions as a consequence of climate feedbacks.”
He explained that for a new patch of deforestation in the Amazon, the regional climate changes that happen as a result led to an additional 5.1 percent more loss of total biomass in the entire Amazon basin. In the Congo, the additional biomass loss from the climate effects of deforestation is about 3.8 percent. Tropical forests store about 200 petagrams of carbon in their aboveground biomass. Since 2010, deforestation has been removing about 1 petagram of that carbon every year. (One petagram is equal to 1 trillion kilograms.)
Until now, climate modelers have, for lack of data, not considered tree mortality in their climate simulations. But by combining satellite data with climate variables, they obtained information about how sensitive carbon stored in vegetation is to climatic changes that result from tree mortality and fire.
“Deforestation has ramifications to forests growing elsewhere, because its consequences to the region’s air temperature and precipitation,” said co-author Paulo Brando, UCI professor of Earth system science. “Until recently, it was very difficult to isolate the effects of deforestation though.”
By developing new estimates of regional carbon losses from deforestation-driven climate change in the Amazon and the Congo, the team provided information that will help scientists fine tune their models. This “might help us design better climate solutions,” Randerson said. By knowing exactly how much biomass is being lost through this activity, he explained, policymakers can make stronger arguments for why it’s worthwhile to curb deforestation, because they can now better describe the knock-on effects.
More information: Yue Li et al, Deforestation-induced climate change reduces carbon storage in remaining tropical forests, Nature Communications (2022). DOI: 10.1038/s41467-022-29601-0
Journal information: Nature Communications
Provided by University of California, Irvine.
A new study in Environmental Research Letters shows striking disparities in the distribution of conserved land across multiple dimensions of social marginalization in New England—and creates a tool to help address them.
In a New England-wide analysis, the researchers found that communities in the lowest income quartile, and communities with the highest proportions of people of color have access to only about half as much protected land near where they live. These disparities persist across urban, suburban, and rural communities, and across decades.
“This is consistent with the very long history of exclusion and marginalization in conservation efforts,” says Boston-based social justice scholar Neenah Estrella-Luna, a co-author on the study. “We know that protected open space provides positive opportunities for recreation, social activities, mental and physical health, interactions with nature, food production, and resilience to heat waves. Disparities in access to these benefits that are patterned on race or other characteristics of marginalization require redress. This is a moral imperative.”
But the team, which also included Harvard Forest researchers Lucy Lee and Jonathan Thompson, and Katharine Sims and Margot Lurie (’21) of Amherst College—didn’t stop at identifying the problems. They also created tools that can inform community-led efforts to solve them.
The researchers analyzed lands that rank highly with conventional conservation criteria—such as wildlife habitat, drinking water, and carbon sequestration—and mapped their relationship with lands that rank highly for human environmental justice criteria—including communities with low income, high percentages of people of color, and high percentages of English language learners. They found that the two sometimes don’t overlap, and that future land protection that follows the same patterns as in the past could further deepen environmental justice disparities.
“There are many reasons for protecting land,” explains Lucy Lee, co-author and Harvard Forest Research Assistant. “By analyzing how conservation has played out with specific underlying motivations, we could compare how prioritizing land in different ways would align, or not align, with environmental justice.”
The team created a new prioritization system to help communities, state agencies, and conservation organizations identify specific opportunities for future conservation based on environmental justice criteria. They also built a free, online mapping tool to highlight these opportunities on the landscape.
“Until now, there hasn’t been an explicit way to show how protected areas across the region are distributed in relationship to environmental justice focus areas,” explains co-author Jonathan Thompson, a Senior Ecologist at Harvard Forest. “Several regional conservation groups have already reached out to us, saying they’d like to use this tool as part of their conservation prioritization process.”
The research team emphasizes that this tool is meant to inform and support locally led efforts that center marginalized communities and their self-determined goals.
Estrella-Luna explains, “It’s really important to remember that conservation as we know it began with the explicit idea that the natural environment is only ‘good’ if it is devoid of humans, particularly Indigenous people, other people of color, and poor people. The only way to repair centuries of exclusion, neglect, and marginalization is to make justice and equity central goals of resilience planning.”
Margot Lurie, whose academic internship work at Amherst College helped to catalyze the research, also emphasized the importance of processes for community engagement and consent: “We hope that this tool can both empower local communities interested in protecting nearby land and offer guidance to conservation organizations regarding who needs to be at the table in land-use planning decisions.”
The study highlighted the multiple environmental burdens faced by marginalized communities. Ninety-six percent of the areas identified in the study as environmental justice focus areas contained at least one EPA-listed brownfield site—land where pollutants and contaminants complicate redevelopment.
Despite that, the team points to the importance of restoring existing developed land, including improving forest canopy in marginalized communities, and building new partnerships that can increase access to existing open space.
Lead author Katharine Sims, Professor of Economics and Environmental Studies at Amherst College, notes that there are many ways to improve access that go beyond new land conservation, including better transportation to existing areas, park entry points that are walkable and connected to communities, and stronger support for urban food production spaces. “Conservation organizations are also increasingly understanding that even when greenspace has been available, access has been limited for many by personal experiences of racism or exclusion,” Sims points out. “Changes in leadership structure, outreach, and programming can increase access by making open spaces truly welcoming to all.”
More information: Katharine Sims et al, Environmental justice criteria for new land protection can inform efforts to address disparities in access to nearby open space, Environmental Research Letters (2022). DOI: 10.1088/1748-9326/ac6313
Mapping tool: harvard-cga.maps.arcgis.com/ap … 4918895b59de4e9842cb
Journal information: Environmental Research Letters
Provided by Harvard University.
If nations do all that they’ve promised to fight climate change, the world can still meet one of two internationally agreed upon goals for limiting warming. But the planet is blowing past the other threshold that scientists say will protect Earth more, a new study finds.
The world is potentially on track to keep global warming at, or a shade below, 2 degrees Celsius (3.6 degrees Fahrenheit) hotter than pre-industrial times, a goal that once seemed out of reach, according to a study published Wednesday in the journal Nature.
That will only happen if countries not only fulfill their specific pledged national targets for curbing carbon emissions by 2030, but also come through on more distant promises of reaching net zero carbon emissions by mid-century, the study says.
This 2 degree warmer world still represents what scientists characterize as a profoundly disrupted climate with fiercer storms, higher seas, animal and plant extinctions, disappearing coral, melting ice and more people dying from heat, smog and infectious disease. It’s not the goal that world leaders say they really want: 1.5 degrees Celsius (2.7 degrees Fahrenheit) since pre-industrial times. The world will blast past that more prominent and promoted goal unless dramatic new emission cuts are promised and achieved this decade and probably within the next three years, study authors said.
Both goals of 1.5-degrees and 2-degrees are part of the 2015 Paris climate pact and the 2021 Glasgow follow-up agreement. The 2-degree goal goes back years earlier.
“For the first time we can possibly keep warming below the symbolic 2-degree mark with the promises on the table. That assumes of course that the countries follow through on the promises,” said study lead author Malte Meinshausen, a University of Melbourne climate scientist.
That’s a big if, outside climate scientists and the authors, say. It means political leaders actually doing what they promise
The study “examines only this optimistic scenario. It does not check whether governments are making efforts to implement their long-term targets and whether they are credible,” said Niklas Hohne of Germany, a New Climate Institute scientist who analyzes pledges for Climate Action Tracker and wasn’t part of this study. “We know that governments are far from implementing their long-term targets.”
Hohne’s team and others who track pledges have similarly found that limiting warming to 2 degrees is still possible, as Meinshausen’s team has. The difference is that Meinshausen’s study is the first to be peer-reviewed and published in a scientific journal.
Sure, the 2-degree world requires countries to do what they promise. But cheaper wind and solar have shown carbon emissions cuts can come faster than thought and some countries will exceed their promised cuts, Meinshausen said. He also said the way climate action works is starting with promises and then policies, so it’s not unreasonable to take countries at their word.
Mostly, he said, limiting warming to 2 degrees is still a big improvement compared to just five or ten years ago, when “everybody laughed like ‘ha we’ll never see targets on the table that bring us closer to 2 degrees’,” Meinshausen said. “Targets and implemented policies actually can turn the needle on future temperatures. I think that optimism is important for countries to see. Yes, there is hope.”
About 20% to 30% of that hope is due to the Paris climate agreement, but the rest is due to earlier investments by countries that made green energy technologies cheaper than dirty fossil fuels such as coal, oil and natural gas, Meinshausen said.
Yet, even if that’s good news, it’s not all good, he said.
“Neither do we have a margin of error (on barely limiting to 2 degrees) nor do the pledges put us on a path close to 1.5 degrees,” Meinshausen said.
In 2018 the United Nations’ scientific expert team studied the differences between the 1.5- and 2-degree thresholds and found considerably worse and more extensive damages to Earth at 2 degrees of warming. So the world has recently tried to make the 1.5 degrees goal possible.
Earth has already warmed at least 1.1 degrees Celsius (2 degrees Fahrenheit) since pre-industrial times, often considered the late 1800s, so 2 degrees of warming really means another 0.9 degrees Celsius (1.6 degrees Fahrenheit) hotter than now.
Meinshausen’s analysis “looks good and solid, but there are always assumptions that could be important,” said Glen Peters, a climate scientist who tracks emissions with Global Carbon Project.
The biggest assumption is that nations somehow get to promised net zero carbon emissions, most of them by 2050 but a decade or two later for China and India, said Peters, research director of the Cicero Center for International Climate Research in Oslo, Norway.
“Making pledges for 2050 is cheap, backing them up with necessary short-term action is hard,” he said, noting that for most countries, there will be five or six elections between now and 2050.
More information: Malte Meinshausen et al, Realization of Paris Agreement pledges may limit warming just below 2 °C, Nature (2022). DOI: 10.1038/s41586-022-04553-z
Zeke Hausfather et al, Net-zero commitments could limit warming to below 2 °C, Nature (2022). DOI: 10.1038/d41586-022-00874-1
Journal information: Nature.
Minerals trapped inside tiny crystals that have survived the grinding of the continents over billions of years may help to reveal the origins of plate tectonics and perhaps even provide clues about how complex life sprang up on Earth.
The theory of plate tectonics—which describes how the Earth’s crust is separated into plates that float and slide on a layer of malleable rock below—became widely accepted by science around 50 years ago. The process is believed to have largely shaped the world around us by enabling continents to form, throwing up enormous mountain ranges when they collide, creating volcanic islands and triggering catastrophic earthquakes.
But there is still debate about exactly how and when in our planet’s 4.5-billion-year history the plates formed, estimates vary from less than one billion to 4.3 billion years ago.
It is also unclear exactly how quickly plate tectonics evolved, says Dr. Hugo Moreira, a geologist at the University of Montpellier in France. Did Earth’s crust split abruptly into multiple plates and start moving over just tens of millions of years, or was the process far more gradual, taking hundreds of millions of years or more?
Understanding this could prove crucial for understanding not just how the planet itself has evolved, but also how life may have been kickstarted on Earth. The conditions created by plate tectonics are thought to have helped make Earth hospitable to life in the first place and also provided vital nutrients needed for complex multicellular life to prosper.
Crystal time capsules
Dr. Moreira and his colleagues are seeking answers to these questions inside tiny zircon crystals, which are time capsules of Earth’s distant past due to their extreme robustness. They are often found preserved in rock despite the action of continual weathering and geological events.
Many of these crystals have previously been dated by analysing the radioactive decay of isotopes—different forms of elements—that they contain. Some have been found to date as far back as 4.4 billion years ago, the earliest known fragments of Earth’s crust.
“That’s why zircon’s amazing, because although the rocks that compose the continents were destroyed, the zircon survived in the sedimentary record,” said Dr. Moreira. Scientists have previously used zircon crystals to study the history of the Earth’s continental crust, but it has not yet been enough to provide a definitive consensus for how plate tectonics started, he says.
“After analysing hundreds of thousands of them, we still do not have an agreement,” said Dr. Moreira, a member of the MILESTONE project being led by Dr. Bruno Dhuime, a geosciences researcher for the French National Centre for Scientific Research also at the University of Montpellier.
The researchers are hoping to use these crystals—which typically measure about a tenth of a millimetre, or roughly the thickness of a human hair—to improve our insight into the timing and evolution of plate tectonics.
The MILESTONE group will drill down to an even tinier scale—about a hundredth of a millimetre—to examine traces of apatite and feldspar minerals trapped inside the zircon crystals. Strontium and lead isotopes in these ‘inclusions’ can add unprecedented detail on the zircon’s source of formation and whether this occurred in the varying types of magma below stagnant or moving plates, says Dr. Moreira.
“It will be a critical step towards a better understanding of how our planet evolved,” he said. “If we manage to measure the isotopic composition of these tiny inclusions, we might tell what was the composition of the rock from which the zircon crystallised. We can perhaps understand how evolved the crust was at that point and in which type of tectonic settings the magma was formed.”
This tiny-scale analysis been made possible by the set-up of a laboratory containing a specialised, highly sensitive mass spectrometer, equipment that measures the characteristics of atoms.
The team hopes to start analysing samples next month, ultimately investigating inclusions in more than 5,000 zircons of varying age from all over the world to build up a wide-scale picture. “What we want to do is pinpoint when plate tectonics went global instead of when it was localised in isolated points here and there,” said Dr. Moreira.
Underground structures
At the opposite end of the scale, other researchers have been seeking clues to the origins of plate tectonics in two massive continent-sized structures found deep underground beneath the Pacific and African plates.
These ‘thermochemical piles,” mysterious structures located about 2,900 kilometres below the surface at the boundary between Earth’s core and mantle, were discovered in the 1990s with the aid of seismic tomography—imaging from seismic waves produced by earthquakes or explosions. They were detected as potentially warmer areas of material in which seismic waves travel at different speeds than in the surrounding mantle, but there is still much debate about exactly what they are, including their composition, longevity, shape and origins.
Over the past couple of decades, a ‘fiery’ debate has arisen over their proposed link to movements on the planet’s surface and so their potential involvement in the emergence of plate tectonics, explained Dr. Philip Heron, a geoscientist who studied the structures as lead researcher on the TEROPPLATE project at Durham University.
“These piles are thought to have an impact on how material moves within the planet, and therefore how the surface behaves over time,” he said. Events on the surface may in turn drive their activity.
One theory is that these piles are stable for long geological periods and their edges correspond with the position of key features involved in plate tectonics on Earth’s surface, such as supervolcanoes.
However, their extreme depth makes these piles difficult to observe directly. “Given that these structures are in places 100 times higher than Mount Everest, they may be the largest things in our planet that we know the least about,” said Dr. Heron.
Supercomputer power
The TEROPPLATE project harnessed supercomputer power to investigate. Using more than 1,000 computers working in tandem, the team developed 3-D models of Earth to show how the assumed chemical composition of large hot regions deep underground might influence the formation and location of deep mantle plumes.
However, their models indicated that the piles may be more passive in plate tectonics than initially thought and that the world would still form similar geological features without them. “When looking at the positioning of large plumes of material that form supervolcanoes, our numerical simulations indicated that the chemical piles were not the controlling factor in this,” said Dr. Heron.
But he added that these findings were not fully conclusive and have also opened the door to other interesting avenues for research—such as exploring the implications that these structures are constantly moving through the mantle rather than being largely stationary.
“It gives weight to the theory that the chemical piles may not be rigid and fixed in our planet, and that the deep Earth may evolve as readily as the continents on our surface move around,” he said. “It’s a push to start looking deeper.”
Some of TEROPPLATE’s results also indicate that the piles may have been robust enough to survive Earth’s earliest beginnings. That makes it feasible for them to have been around for the start of plate tectonics and thus to have had roles in the process that we don’t yet know about, adds Dr. Heron.
All of this could have implications for understanding our own place on Earth too. If, for instance, plate tectonics evolved rapidly early in Earth’s history, it may raise questions such as why complex life didn’t emerge earlier or just how closely the two are linked, says Dr. Moreira.
“To fundamentally understand where plate tectonics comes from is potentially the essence of life,” added Dr. Heron. “On Earth, there’s not a thing that hasn’t been impacted by it.”
The Witwatersrand Basin in South Africa holds the world’s largest gold deposits across a 200-km long swathe. Individual ore deposits are spread out in thin layers over areas up to 10 by 10 km and contain more gold than any other gold deposit in the world. Some 40% of the precious metal that has been found up to the present day comes from this area, and hundreds of tons of gold deposits still lie beneath the earth. The manner in which these giant deposits formed is still debated among geologists. Christoph Heinrich, Professor of Mineral Resources at ETH and the University of Zurich, recently published a new explanation in the journal Nature Geoscience, trying to reconcile the contradictions of two previously published theories.
The prevailing ‘placer gold’ theory states that the gold at Witwatersrand was transported and concentrated through mechanical means as metallic particles in river sediment. Such a process has led to the gold-rich river gravels that gave rise to the Californian gold rush. Here, nuggets of placer gold have accumulated locally in river gravels in the foothills of the Sierra Nevada, where primary gold-quarz veins provide a nearby source of the nuggets.
But no sufficiently large source exists in the immediate sub-surface of the Witwatersrand Basin. This is one of the main arguments of proponents of the ‘hydrothermal hypothesis’, according to which gold, chemically dissolved in hot fluid, passed into the sediment layers half a billion years after their deposition. For this theory to work, a 10 km thick blanket of later sediments would be required in order to create the required pressure and temperature. However, the hydrothermal theory is contradicted by geological evidence that the gold concentration must have taken place during the formation of host sediments on the Earth’s surface.
Rainwater rich in hydrogen sulphide
Heinrich believes the concentration of gold took place at the Earth’s surface, indeed by flowing river water, but in chemically dissolved form. With such a process, the gold could be easily ‘collected’ from a much larger catchment area of weathered, slightly gold-bearing rocks. The resource geologist examined the possibility of this middle way, by calculating the chemical solubility of the precious metal in surface water under the prevailing atmospheric and climatic conditions.
Experimental data shows that the chemical transport of gold was indeed possible in the early stages of Earth evolution. The prerequisite was that the rainwater had to be at least occasionally very rich in hydrogen sulphide. Hydrogen sulphide binds itself in the weathered soil with widely distributed traces of gold to form aqueous gold sulphide complexes, which significantly increases the solubility of the gold. However, hydrogen sulphide in the atmosphere and sulphurous gold complexes in river water are stable only in the absence of free oxygen. “Quite inhospitable environmental conditions must have dominated, which was possible only three billion years ago during the Archean eon,” says Heinrich. “It required an oxygen-free atmosphere that was temporarily very rich in hydrogen sulphide — the smell of rotten eggs.” In today’s atmosphere, oxygen oxidises all hydrogen sulphide, thus destroying gold’s sulphur complex in a short time, which is why gold is practically insoluble in today’s river water.
Volcanoes and bacteria as important factors
In order to increase the sulphur concentration of rainwater sufficiently in the Archean eon, basaltic volcanism of gigantic proportions was required at the same time. Indeed, in other regions of South Africa there is evidence of giant basaltic eruptions overlapping with the period of the gold concentration.
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A third factor required for the formation of gold deposits at Witwatersrand is a suitable location for concentrated precipitation of the gold. The richest deposits of gold ore in the basin are found in carbon-rich layers, often just millimetres to centimeters thick, but which stretch for many kilometres. These thin layers contain such high gold concentrations that mining tunnels scarcely a metre high some three kilometres below the Earth’s surface are still worthwhile.
The carbon probably stems from the growth of bacteria on the bottom of shallow lakes and it’s here that the dissolved gold precipitated chemically, according to Heinrich’s interpretation.
The nature of these life forms is not well known. “It’s possible that these primitive organisms actively adsorbed the gold,” Heinrich speculates. “But a simple chemical reduction of sulphur-complexed gold in water to elementary metal on an organic material is sufficient for a chemical ‘gilding’ of the bottom of the shallow lakes.”
The gold deposits in the Witwatersrand, which are unique worldwide, could have thus been formed only during a certain period of the Earth’s history: after the development of the first continental life forms in shallow lakes at least 3 billion years ago, but before the first emergence of free oxygen in the Earth’s atmosphere approximately 2.5 billion years ago.
Reference:
Christoph A. Heinrich. Witwatersrand gold deposits formed by volcanic rain, anoxic rivers and Archaean life. Nature Geoscience, 2015; DOI: 10.1038/ngeo2344
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