POSTMODERN ALCHEMY

Hydrogen peroxide, universal oxidizing agent, high-efficiency production by simple process

Computer simulation-based catalyst development for hydrogen peroxide production with selectivity of 95%. Development of the platinum-gold alloy catalyst facilitating hydrogen peroxide direct synthesis from hydrogen and oxygen at room temperature and atmo

NATIONAL RESEARCH COUNCIL OF SCIENCE & TECHNOLOGY

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IMAGE: GOLD-PLATINUM NANOPARTICLE COMPOSITE SCHEMATIC view more 

CREDIT: KOREA INSTITUTE OF SCIENCE AND TECHNOLOGY(KIST)

Hydrogen peroxide is used as a disinfectant, after dilution in water, to treat wounds. It is widely used across the industry as an eco-friendly oxidizing agent for impurity removal from semiconductors, waste treatment, etc. Currently, it is mainly produced by the sequential hydrogenation and oxidation of anthraquinone (AQ). However, this process is not only energy intensive and requires large-scale facilities, but AQ is also toxic.

As an alternative to the AQ process, hydrogen peroxide direct synthesis from hydrogen (H2) and oxygen (O2) using a palladium (Pd) catalyst was proposed. However, the commercialization of the technology has been challenging becausethe amount of water (H2O) formed is more than hydrogen peroxide (H2O2) during the process.*

*In the case of the Pd catalyst, 40% of hydrogen peroxide and 60% of water were maximally produced.

The Korea Institute of Science and Technology (KIST) announced that a joint research team of Dr. Sang Soo Han and Dr. Donghun Kim (Computational Science Research Center), Dr. Seung Yong Lee (Materials Architecture Research Center), and Professor Kwan-Young Lee at Korea University (Korea University, President Jin Taek Chung) developed a platinum-gold alloy catalyst for hydrogen peroxide production based on a computer simulation. Hydrogen peroxide selectivity can be increased to 95% by using this catalyst, compared with only 30-40% for a palladium catalyst, which indicates that mostly hydrogen peroxide on the developed Pt-Au catalyst can be produced with a small amount of water.

The joint research team between KIST and Korea University developed a new type of Pt-Au alloyed nanoparticle catalyst. Although it is difficult to homogeniously mix Pt and Au to develop an alloyed catalyst due to the intrinsic immiscibility of the metals, the researchers could successfully synthesize nanoparticles in the form of alloys by forcibly reducing **precursors of Pt and Au. Also, using this method, the content of each metal particle could be controlled by adjusting the amount of precursors of Pt and Au.

**Precursor: a substance from which the final specific substances is obtained by metabolism or chemical reactions

Hydrogen peroxide can be produced anywhere without large equipment by simply injecting both hydrogen gas and oxygen gas into an aqueous solution using the catalyst developed by the researchers. Unlike the Pd catalyst, the catalyst developed by the joint researchers can produce hydrogen peroxide up to 95% even at ambient temperature (10 ?C) and atmospheric pressure (1 atm). In addition, a catalytic reaction can be maintained for longer than 8 h, resulting from the structural stability of the catalyst.

The researchers clearly established the crystal structure of Pt-Au alloy nanoparticles by performing additional computer simulations, which is difficult to solve using general material analysis techniques. Furthermore, the catalytic reaction mechanism via compuater simulations was proposed at the atomic level in which the reason why the catalytic performance for hydrogen peroxide production is increased iswith increasing Au content was also clarified.

Sang Soo Han, Head of the Center at KIST, said, "it is important that the developed catalysts provide an eco-friendly hydrogen peroxide production option that can be applied without any limitation of manufacturing sites. Therefore, commercialization for the hydrogen peroxide direct synthesis would be greatly accelerated by overcoming the limitation of Pd catalysts with the low selectivity" and "the time and cost for the development of novel catalysts, mainly explored through trial and error, could be considerably reduced through computer simulations".

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This study was conducted by the Creative Materials Discovery Program of the National Research Foundation of Korea with the support of the Ministry of Science and ICT (MSIT).The research results were published in the latest issue of an international journal 'Acta Materialia' in the field of materials science.

 

Biotech fit for the Red Planet

New method for growing cyanobacteria under Mars-like conditions

FRONTIERS

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IMAGE: A: BIOREACTOR ATMOS ( "ATMOSPHERE TESTER FOR MARS-BOUND ORGANIC SYSTEMS "). B: A SINGLE VESSEL WITHIN ATMOS. C: DESIGN SCHEMATIC view more 

CREDIT: C. VERSEUX / ZARM

NASA, in collaboration with other leading space agencies, aims to send its first human missions to Mars in the early 2030s, while companies like SpaceX may do so even earlier. Astronauts on Mars will need oxygen, water, food, and other consumables. These will need to be sourced from Mars, because importing them from Earth would be impractical in the long term. In Frontiers in Microbiology, scientists show for the first time that Anabaena cyanobacteria can be grown with only local gases, water, and other nutrients and at low pressure. This makes it much easier to develop sustainable biological life support systems.

"Here we show that cyanobacteria can use gases available in the Martian atmosphere, at a low total pressure, as their source of carbon and nitrogen. Under these conditions, cyanobacteria kept their ability to grow in water containing only Mars-like dust and could still be used for feeding other microbes. This could help make long-term missions to Mars sustainable," says lead author Dr Cyprien Verseux, an astrobiologist who heads the Laboratory of Applied Space Microbiology at the Center of Applied Space Technology and Microgravity (ZARM) of the University of Bremen, Germany.

Low-pressure atmosphere

Cyanobacteria have long been targeted as candidates to drive biological life support on space missions, as all species produce oxygen through photosynthesis while some can fix atmospheric nitrogen into nutrients. A difficulty is that they cannot grow directly in the Martian atmosphere, where the total pressure is less than 1% of Earth's - 6 to 11 hPa, too low for the presence of liquid water - while the partial pressure of nitrogen gas - 0.2 to 0.3 hPa - is too low for their metabolism. But recreating an Earth-like atmosphere would be expensive: gases would need to be imported, while the culture system would need to be robust - hence, heavy to freight - to resist the pressure differences: "Think of a pressure cooker," Verseux says. So the researchers looked for a middle ground: an atmosphere close to Mars's which allows the cyanobacteria to grow well.

To find suitable atmospheric conditions, Verseux et al. developed a bioreactor called Atmos (for "Atmosphere Tester for Mars-bound Organic Systems"), in which cyanobacteria can be grown in artificial atmospheres at low pressure. Any input must come from the Red Planet itself: apart from nitrogen and carbon dioxide, gases abundant in the Martian atmosphere, and water which could be mined from ice, nutrients should come from "regolith", the dust covering Earth-like planets and moons. Martian regolith has been shown to be rich in nutrients such as phosphorus, sulphur, and calcium.

Anabaena: versatile cyanobacteria grown on Mars-like dust

Atmos has nine 1 L vessels made of glass and steel, each of which is sterile, heated, pressure-controlled, and digitally monitored, while the cultures inside are continuously stirred. The authors chose a strain of nitrogen-fixing cyanobacteria called Anabaena sp. PCC 7938, because preliminary tests showed that it would be particularly good at using Martian resources and helping to grow other organisms. Closely related species have been shown to be edible, suitable for genetic engineering, and able to form specialized dormant cells to survive harsh conditions.

Verseux and his colleagues first grew Anabaena for 10 days under a mixture of 96% nitrogen and 4% carbon dioxide at a pressure of 100 hPa - ten times lower than on Earth. The cyanobacteria grew as well as under ambient air. Then they tested the combination of the modified atmosphere with regolith. Because no regolith has ever been brought from Mars, they used a substrate developed by the University of Central Florida (called "Mars Global Simulant") instead to create a growth medium. As controls, Anabaena were grown in standard medium, either at ambient air or under the same low-pressure artificial atmosphere.

The cyanobacteria grew well under all conditions, including in regolith under the nitrogen- and carbon dioxide-rich mixture at low pressure. As expected, they grew faster on standard medium optimized for cyanobacteria than on Mars Global Simulant, under either atmosphere. But this is still a major success: while standard medium would need to be imported from Earth, regolith is ubiquitous on Mars. "We want to use as nutrients resources available on Mars, and only those," says Verseux.

Dried Anabaena biomass was ground, suspended in sterile water, filtered, and successfully used as a substrate for growing of E. coli bacteria, proving that sugars, amino acids, and other nutrients can be extracted from them to feed other bacteria, which are less hardy but tried-and-tested tools for biotechnology. For example, E. coli could be engineered more easily than Anabaena to produce some food products and medicines on Mars that Anabaena cannot.

The researchers conclude that nitrogen-fixing, oxygen-producing cyanobacteria can be efficiently grown on Mars at low pressure under controlled conditions, with exclusively local ingredients.

Further refinements in the pipeline

These results are an important advance. But the authors caution that further studies are necessary: "We want to go from this proof-of-concept to a system that can be used on Mars efficiently," Verseux says. They suggest fine-tuning the combination of pressure, carbon dioxide, and nitrogen optimal for growth, while testing other genera of cyanobacteria, perhaps genetically tailored for space missions. A cultivation system for Mars also needs to be designed:

"Our bioreactor, Atmos, is not the cultivation system we would use on Mars: it is meant to test, on Earth, the conditions we would provide there. But our results will help guide the design of a Martian cultivation system. For example, the lower pressure means that we can develop a more lightweight structure that is more easily freighted, as it won't have to withstand great differences between inside and outside," concludes Verseux.

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The project was funded by the Alexander von Humboldt Foundation.

Strange creatures accidentally discovered beneath Antarctica's ice shelves

FRONTIERS

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IMAGE: BRITISH ANTARCTIC SURVEY CAMERA TRAVELLING DOWN THE 900-METER-LONG BORE HOLE IN THE FILCHNER-RONNE ICE SHELF. (MARINE CREATURE PICTURED IS UNRELATED TO THE DISCOVERY) view more 

CREDIT: DR HUW GRIFFITHS/BRITISH ANTARCTIC SURVEY

Far underneath the ice shelves of the Antarctic, there's more life than expected, finds a recent study in the journal Frontiers in Marine Science.

During an exploratory survey, researchers drilled through 900 meters of ice in the Filchner-Ronne Ice Shelf, situated on the south eastern Weddell Sea. At a distance of 260km away from the open ocean, under complete darkness and with temperatures of -2.2°C, very few animals have ever been observed in these conditions.

But this study is the first to discover the existence of stationary animals - similar to sponges and potentially several previously unknown species - attached to a boulder on the sea floor.

"This discovery is one of those fortunate accidents that pushes ideas in a different direction and shows us that Antarctic marine life is incredibly special and amazingly adapted to a frozen world," says biogeographer and lead author, Dr Huw Griffiths of British Antarctic Survey.

More questions than answers

"Our discovery raises so many more questions than it answers, such as how did they get there? What are they eating? How long have they been there? How common are these boulders covered in life? Are these the same species as we see outside the ice shelf or are they new species? And what would happen to these communities if the ice shelf collapsed?"

Floating ice shelves represent the greatest unexplored habitat in the Southern Ocean. They cover more that 1.5m sq km of the Antarctic continental shelf, but only a total area similar in size to a tennis court has been studied through eight prior boreholes.

Current theories on what life could survive under ice shelves suggest that all life becomes less abundant as you move further away from open water and sunlight. Past studies have found some small mobile scavengers and predators, such as fish, worms, jellyfish or krill, in these habitats. But filter feeding organisms - which depend on a supply of food from above - were expected to be amongst the first to disappear further under the ice.

So, it came as a surprise when the team of geologists, drilling through the ice to collect sediment samples, hit a rock instead of mud at the bottom of the ocean below. They were even more surprised by the video footage, which showed a large boulder covered in strange creatures.

New Antarctic expedition needed

This is the first ever record of a hard substrate (ie a boulder) community deep beneath an ice shelf and it appears to go against all previous theories of what types of life could survive there.

Given the water currents in the region, the researchers calculate that this community may be as much as 1,500km upstream from the closest source of photosynthesis. Other organisms are also known to collect nutrients from glacial melts or chemicals from methane seeps, but the researchers won't know more about these organisms until they have the tools to collect samples of these organisms--a significant challenge in itself.

"To answer our questions we will have to find a way of getting up close with these animals and their environment - and that's under 900 meters of ice, 260km away from the ships where our labs are," continues Griffiths. "This means that as polar scientists, we are going to have to find new and innovative ways to study them and answer all the new questions we have."

Griffiths and the team also note that with the climate crisis and the collapse of these ice shelves, time is running out to study and protect these ecosystems

CAPTION

Stationary animals - similar to sponges and potentially several previously unknown species - attached to a boulder on the sea floor.

CREDIT

Dr Huw Griffiths/British Antarctic Survey

Neanderthals and Homo sapiens used identical Nubian technology

MAX PLANCK INSTITUTE FOR THE SCIENCE OF HUMAN HISTORY

Research News

 

IMAGE: THE VIEW FROM SHUKBAH CAVE view more 

CREDIT: AMOS FRUMKIN

Long held in a private collection, the newly analysed tooth of an approximately 9-year-old Neanderthal child marks the hominin's southernmost known range. Analysis of the associated archaeological assemblage suggests Neanderthals used Nubian Levallois technology, previously thought to be restricted to Homo sapiens.

With a high concentration of cave sites harbouring evidence of past populations and their behaviour, the Levant is a major centre for human origins research. For over a century, archaeological excavations in the Levant have produced human fossils and stone tool assemblages that reveal landscapes inhabited by both Neanderthals and Homo sapiens, making this region a potential mixing ground between populations. Distinguishing these populations by stone tool assemblages alone is difficult, but one technology, the distinct Nubian Levallois method, is argued to have been produced only by Homo sapiens.

In a new study published in Scientific Reports, researchers from the Max Planck Institute for the Science of Human History teamed up with international partners to re-examine the fossil and archaeological record of Shukbah Cave. Their findings extend the southernmost known range of Neanderthals and suggest that our now-extinct relatives made use of a technology previously argued to be a trademark of modern humans. This study marks the first time the lone human tooth from the site has been studied in detail, in combination with a major comparative study examining the stone tool assemblage.

"Sites where hominin fossils are directly associated with stone tool assemblages remain a rarity - but the study of both fossils and tools is critical for understanding hominin occupations of Shukbah Cave and the larger region," says lead author Dr Jimbob Blinkhorn, formerly of Royal Holloway, University of London and now with the Pan-African Evolution Research Group (Max Planck Institute for the Science of Human History).

Shukbah Cave was first excavated in the spring of 1928 by Dorothy Garrod, who reported a rich assemblage of animal bones and Mousterian-style stone tools cemented in breccia deposits, often concentrated in well-marked hearths. She also identified a large, unique human molar. However, the specimen was kept in a private collection for most of the 20th century, prohibiting comparative studies using modern methods. The recent re-identification of the tooth at the Natural History Museum in London has led to new detailed work on the Shukbah collections.

CAPTION

Photos of Nubian Levallois cores associated with Neanderthal fossils. Copyright: UCL, Institute of Archaeology & courtesy of the Penn Museum, University of Pennsylvania

CREDIT

Blinkhorn, et al., 2021 / CC BY 4.0

"Professor Garrod immediately saw how distinctive this tooth was. We've examined the size, shape and both the external and internal 3D structure of the tooth, and compared that to Holocene and Pleistocene Homo sapiens and Neanderthal specimens. This has enabled us to clearly characterise the tooth as belonging to an approximately 9 year old Neanderthal child," says Dr. Clément Zanolli, from Université de Bordeaux. "Shukbah marks the southernmost extent of the Neanderthal range known to date," adds Zanolli.

Although Homo sapiens and Neanderthals shared the use of a wide suite of stone tool technologies, Nubian Levallois technology has recently been argued to have been exclusively used by Homo sapiens. The argument has been made particularly in southwest Asia, where Nubian Levallois tools have been used to track human dispersals in the absence of fossils.

"Illustrations of the stone tool collections from Shukbah hinted at the presence of Nubian Levallois technology so we revisited the collections to investigate further. In the end, we identified many more artefacts produced using the Nubian Levallois methods than we had anticipated," says Blinkhorn. "This is the first time they've been found in direct association with Neanderthal fossils, which suggests we can't make a simple link between this technology and Homo sapiens."

"Southwest Asia is a dynamic region in terms of hominin demography, behaviour and environmental change, and may be particularly important to examine interactions between Neanderthals and Homo sapiens," adds Prof Simon Blockley, of Royal Holloway, University of London. "This study highlights the geographic range of Neanderthal populations and their behavioural flexibility, but also issues a timely note of caution that there are no straightforward links between particular hominins and specific stone tool technologies."

"Up to now we have no direct evidence of a Neanderthal presence in Africa," said Prof Chris Stringer of the Natural History Museum. "But the southerly location of Shukbah, only about 400 km from Cairo, should remind us that they may have even dispersed into Africa at times."

CAPTION

Photo and 3D reconstruction of a tooth of a 9-year-old Neanderthal child. Copyright: Trustees of the Natural History Museum, London

CREDIT

Blinkhorn, et al., 2021 / CC BY 4.0

Partnerships

Researchers involved in this study include scholars from the Max Planck Institute for the Science of Human History, Royal Holloway, University of London, the Université de Bordeaux, the Max Planck Institute for Chemical Ecology, the University of Malta, and the Natural History Museum, London. This work was supported by the Leverhulme trust (RPH-2017-087).

Comet or asteroid: What killed the dinosaurs and where did it come from?

New theory explains possible origin of the Armageddon-causing object.

HARVARD-SMITHSONIAN CENTER FOR ASTROPHYSICS

Research News

 

IMAGE: ARTIST'S RENDERING OF A COMET HEADED TOWARDS EARTH. view more 

CREDIT: CREDIT NOT REQUIRED. THIS IS A PUBLIC DOMAIN IMAGE.

It forever changed history when it crashed into Earth about 66 million years ago.

The Chicxulub impactor, as it's known, left behind a crater off the coast of Mexico that spans 93 miles and runs 12 miles deep. Its devastating impact brought the reign of the dinosaurs to an abrupt and calamitous end by triggering their sudden mass extinction, along with the end of almost three-quarters of the plant and animal species living on Earth.

The enduring puzzle: Where did the asteroid or comet originate, and how did it come to strike Earth? Now, a pair of researchers at the Center for Astrophysics | Harvard & Smithsonian believe they have the answer.

In a study published today in Nature's Scientific Reports, Harvard University astrophysics undergraduate student Amir Siraj and astronomer Avi Loeb put forth a new theory that could explain the origin and journey of this catastrophic object.

Using statistical analysis and gravitational simulations, Siraj and Loeb calculate that a significant fraction of long-period comets originating from the Oort cloud, an icy sphere of debris at the edge of the solar system, can be bumped off-course by Jupiter's gravitational field during orbit.

"The solar system acts as a kind of pinball machine," explains Siraj, who is pursuing bachelor's and master's degrees in astrophysics, in addition to a master's degree in piano performance at the New England Conservatory of Music. "Jupiter, the most massive planet, kicks incoming long-period comets into orbits that bring them very close to the sun."

During close passage to the sun, the comets -- nicknamed "sungrazers" --can experience powerful tidal forces that break apart pieces of the rock and ultimately, produce cometary shrapnel.

"In a sungrazing event, the portion of the comet closer to the sun feels a stronger gravitational pull than the part that is further, resulting in a tidal force across the object," Siraj says. "You can get what's called a tidal disruption event, in which a large comet breaks up into many smaller pieces. And crucially, on the journey back to the Oort cloud, there's an enhanced probability that one of these fragments hit the Earth."

The new calculations from Siraj and Loeb's theory increase the chances of long-period comets impacting Earth by a factor of about 10, and show that about 20 percent of long-period comets become sungrazers.

The pair say that their new rate of impact is consistent with the age of Chicxulub, providing a satisfactory explanation for its origin and other impactors like it.

"Our paper provides a basis for explaining the occurrence of this event," Loeb says. "We are suggesting that, in fact, if you break up an object as it comes close to the sun, it could give rise to the appropriate event rate and also the kind of impact that killed the dinosaurs."

Evidence found at the Chicxulub crater suggests the rock was composed of carbonaceous chondrite. Siraj and Loeb's hypothesis might also explain this unusual composition.

A popular theory on the origin of Chicxulub claims that the impactor originated from the main belt, which is an asteroid population between the orbit of Jupiter and Mars. However, carbonaceous chondrites are rare amongst main-belt asteroids, but possibly widespread amongst long-period comets, providing additional support to the cometary impact hypothesis.

Other similar craters display the same composition. This includes an object that hit about 2 billion years ago and left the Vredefort crater in South Africa, which is the largest confirmed crater in Earth's history, and the impactor that left the Zhamanshin crater in Kazakhstan, which is the largest confirmed crater within the last million years. The researchers say that the timing of these impacts support their calculations on the expected rate of Chicxulub-sized tidally disrupted comets.

Siraj and Loeb say their hypothesis can be tested by further studying these craters, others like them, and even ones on the surface of the moon to determine the composition of the impactors. Space missions sampling comets can also help.

Aside from composition of comets, the new Vera Rubin Observatory in Chile may be able to observe tidal disruption of long-period comets after it becomes operational next year.

"We should see smaller fragments coming to Earth more frequently from the Oort cloud," Loeb says. "I hope that we can test the theory by having more data on long-period comets, get better statistics, and perhaps see evidence for some fragments."

Loeb says understanding this is not just crucial to solving a mystery of Earth's history but could prove pivotal if such an event were to threaten the planet.

"It must have been an amazing sight, but we don't want to see that again," he said.

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This work was partially supported by the Harvard Origins of Life Initiative and the Breakthrough Prize Foundation.

About the Center for Astrophysics | Harvard & Smithsonian

The Center for Astrophysics | Harvard & Smithsonian is a collaboration between Harvard and the Smithsonian designed to ask--and ultimately answer--humanity's greatest unresolved questions about the nature of the universe. The Center for Astrophysics is headquartered in Cambridge, MA, with research facilities across the U.S. and around the world.

The comet that killed the dinosaurs

New theory explains possible origin of the Chicxulub impactor

HARVARD UNIVERSITY

Research News

 

IMAGE: A COMET PLUNGING THROUGH EARTH'S ATMOSPHERE. view more 

CREDIT: GERD ALTMANN/PIXABAY

It was tens of miles wide and forever changed history when it crashed into Earth about 66 million years ago.

The Chicxulub impactor, as it's known, left behind a crater off the coast of Mexico that spans 93 miles and goes 12 miles deep. Its devastating impact brought the reign of the dinosaurs to an abrupt and calamitous end by triggering their sudden mass extinction, along with the end of almost three-quarters of the plant and animal species then living on Earth.

The enduring puzzle has always been where the asteroid or comet that set off the destruction originated, and how it came to strike the Earth. And now a pair of Harvard researchers believe they have the answer.

In a study published in Scientific Reports, Avi Loeb, Frank B. Baird Jr. Professor of Science at Harvard, and Amir Siraj '21, an astrophysics concentrator, put forth a new theory that could explain the origin and journey of this catastrophic object and others like it.

Using statistical analysis and gravitational simulations, Loeb and Siraj show that a significant fraction of a type of comet originating from the Oort cloud, a sphere of debris at the edge of the solar system, was bumped off-course by Jupiter's gravitational field during its orbit and sent close to the sun, whose tidal force broke apart pieces of the rock. That increases the rate of comets like Chicxulub (pronounced Chicks-uh-lub) because these fragments cross the Earth's orbit and hit the planet once every 250 to 730 million years or so.

"Basically, Jupiter acts as a kind of pinball machine," said Siraj, who is also co-president of Harvard Students for the Exploration and Development of Space and is pursuing a master's degree at the New England Conservatory of Music. "Jupiter kicks these incoming long-period comets into orbits that bring them very close to the sun."

It's because of this that long-period comets, which take more than 200 years to orbit the sun, are called sun grazers, he said.

"When you have these sun grazers, it's not so much the melting that goes on, which is a pretty small fraction relative to the total mass, but the comet is so close to the sun that the part that's closer to the sun feels a stronger gravitational pull than the part that is farther from the sun, causing a tidal force" he said. "You get what's called a tidal disruption event and so these large comets that come really close to the sun break up into smaller comets. And basically, on their way out, there's a statistical chance that these smaller comets hit the Earth."

The calculations from Loeb and Siraj's theory increase the chances of long-period comets impacting Earth by a factor of about 10, and show that about 20 percent of long-period comets become sun grazers. That finding falls in line with research from other astronomers.

The pair claim that their new rate of impact is consistent with the age of Chicxulub, providing a satisfactory explanation for its origin and other impactors like it.

"Our paper provides a basis for explaining the occurrence of this event," Loeb said. "We are suggesting that, in fact, if you break up an object as it comes close to the sun, it could give rise to the appropriate event rate and also the kind of impact that killed the dinosaurs."

Loeb and Siraj's hypothesis might also explain the makeup of many of these impactors.

"Our hypothesis predicts that other Chicxulub-size craters on Earth are more likely to correspond to an impactor with a primitive (carbonaceous chondrite) composition than expected from the conventional main-belt asteroids," the researchers wrote in the paper.

This is important because a popular theory on the origin of Chicxulub claims the impactor is a fragment of a much larger asteroid that came from the main belt, which is an asteroid population between the orbit of Jupiter and Mars. Only about a tenth of all main-belt asteroids have a composition of carbonaceous chondrite, while it's assumed most long-period comets have it. Evidence found at the Chicxulub crater and other similar craters that suggests they had carbonaceous chondrite.

This includes an object that hit about 2 billion years ago and left the Vredefort crater in South Africa, which is the largest confirmed crater in Earth's history, and the impactor that left the Zhamanshin crater in Kazakhstan, which is the largest confirmed crater within the last million years.

The researchers say that composition evidence supports their model and that the years the objects hit support both their calculations on impact rates of Chicxulub-sized tidally disrupted comets and for smaller ones like the impactor that made the Zhamanshin crater. If produced the same way, they say those would strike Earth once every 250,000 to 730,000 years.

Loeb and Siraj say their hypothesis can be tested by further studying these craters, others like them, and even ones on the surface of the moon to determine the composition of the impactors. Space missions sampling comets can also help.

Aside from composition of comets, the new Vera Rubin Observatory in Chile may be able to see the tidal disruption of long-period comets after it becomes operational next year.

"We should see smaller fragments coming to Earth more frequently from the Oort cloud," Loeb said. "I hope that we can test the theory by having more data on long-period comets, get better statistics, and perhaps see evidence for some fragments."

Loeb said understanding this is not just crucial to solving a mystery of Earth's history but could prove pivotal if such an event were to threaten the planet again.

"It must have been an amazing sight, but we don't want to see that side," he said.

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CO2 dip may have helped dinosaurs walk from South America to Greenland

Climate shift may have aided herbivores on a 6,500-mile trek

EARTH INSTITUTE AT COLUMBIA UNIVERSITY

Research News

IMAGE: A CLIFF IN JAMESON LAND BASIN IN CENTRAL EAST GREENLAND, THE NORTHERNMOST SITE WHERE SAUROPODOMORPH FOSSILS ARE FOUND. THE LABELS POINT OUT SEVERAL SERIES OF LAYERS THAT HELPED THE RESEARCHERS... view more 

CREDIT: LARS CLEMMENSEN

A new paper refines estimates of when herbivorous dinosaurs must have traversed North America on a northerly trek to reach Greenland, and points out an intriguing climatic phenomenon that may have helped them along the journey.

The study, published today in Proceedings of the National Academy of Sciences, is authored by Dennis Kent, adjunct research scientist at Columbia University's Lamont-Doherty Earth Observatory, and Lars Clemmensen from the University of Copenhagen.

Previous estimates suggested that sauropodomorphs -- a group of long-necked, herbivorous dinosaurs that eventually included Brontosaurus and Brachiosaurus -- arrived in Greenland sometime between 225 and 205 million years ago. But by painstakingly matching up ancient magnetism patterns in rock layers at fossil sites across South America, Arizona, New Jersey, Europe and Greenland, the new study offers a more precise estimate: It suggests that sauropodomorphs showed up in what is now Greenland around 214 million years ago. At the time, the continents were all joined together, forming the supercontinent Pangea.

With this new and more precise estimate, the authors faced another question. Fossil records show that sauropodomorph dinosaurs first appeared in Argentina and Brazil about 230 million years ago. So why did it take them so long to expand into the Northern Hemisphere?

"In principle, the dinosaurs could have walked from almost one pole to the other," explained Kent. "There was no ocean in between. There were no big mountains. And yet it took 15 million years. It's as if snails could have done it faster." He calculates that if a dinosaur herd walked only one mile per day, it would take less than 20 years to make the journey between South America and Greenland.

Intriguingly, Earth was in the midst of a tremendous dip in atmospheric CO2 right around the time the sauropodomorphs would have been migrating 214 million years ago. Until about 215 million years ago, the Triassic period had experienced extremely high CO2 levels, at around 4,000 parts per million -- about 10 times higher than today. But between 215 and 212 million years ago, the CO2 concentration halved, dropping to about 2,000ppm.

Although the timing of these two events -- the plummeting CO2 and the sauropodomorph migration -- could be pure coincidence, Kent and Clemmensen think they may be related. In the paper, they suggest that the milder levels of CO2 may have helped to remove climatic barriers that may have trapped the sauropodomorphs in South America.

CAPTION

Map shows how the major continents were arranged 220 million years ago in the Pangea supercontinent. "Isch" and "P" mark locations with sauropodomorph fossils up to 233 million years old. The herbivorous dinosaurs didn't reach Jameson Land in Greenland ("JL") until about 214 million years ago.

CREDIT

Dennis Kent and Lars Clemmensen

On Earth, areas around the equator are hot and humid, while adjacent areas in low latitudes tend to be very dry. Kent and Clemmensen say that on a planet supercharged with CO2, the differences between those climatic belts may have been extreme -- perhaps too extreme for the sauropodomorph dinosaurs to cross.

"We know that with higher CO2, the dry gets drier and the wet gets wetter," said Kent. 230 million years ago, the high CO2 conditions could have made the arid belts too dry to support the movements of large herbivores that need to eat a lot of vegetation to survive. The tropics, too, may have been locked into rainy, monsoon-like conditions that may not have been ideal for sauropodomorphs. There is little evidence they ventured forth from the temperate, mid-latitude habitats they were adapted to in Argentina and Brazil.

But when the CO2 levels dipped 215-212 million years ago, perhaps the tropical regions became more mild, and the arid regions became less dry. There may have been some passageways, such as along rivers and strings of lakes, that would have helped sustain the herbivores along the 6,500-mile journey to Greenland, where their fossils are now abundant. Back then, Greenland would have had a temperate climate similar to New York state's climate today, but with much milder winters, because there were no polar ice sheets at that time.

"Once they arrived in Greenland, it looked like they settled in,'" said Kent. "They hung around as a long fossil record after that."

The idea that a dip in CO2 could have helped these dinosaurs to overcome a climatic barrier is speculative but plausible, and it seems to be supported by the fossil record, said Kent. Sauropodomorph body fossils have not been found in the tropical and arid regions of this time period -- although their footprints do occasionally turn up -- suggesting they did not linger in those areas.

Next, Kent hopes to continue working to better understand the big CO2 dip, including what caused it and how quickly CO2 levels dropped.

CAPTION

A claw of a bipedal sauropodomorph (Plateosaurus) from the Jameson Land site in East Greenland. Parts of the animal were found in 1995 by Farish Jenkins (Harvard), Neil Shubin (U Penn), Lars Clemmensen (Copenhagen), and others. It is the oldest known specimen in the area.

CREDIT

Dennis Kent

Lamont-Doherty Earth Observatory is Columbia University's home for Earth science research. Its scientists develop fundamental knowledge about the origin, evolution and future of the natural world, from the planet's deepest interior to the outer reaches of its atmosphere, on every continent and in every ocean, providing a rational basis for the difficult choices facing humanity. http://www.ldeo.columbia.edu | @LamontEarth

The Earth Institute, Columbia University mobilizes the sciences, education and public policy to achieve a sustainable earth. http://www.earth.columbia.edu.

When the Dalai Lama dies, his reincarnation will be a religious crisis. Here's how it will happen

A decade ago, the Dalai Lama set himself a significant deadline.

© Photo Illustration/getty images

The best-known living Buddhist figure in the world said that when he turned 90 years old, he would decide whether he should be reincarnated -- potentially ending a role that has been key to Tibetan Buddhism for more than 600 years, but in recent decades has become a political lightning rod in China.

While the 14th Dalai Lama, Tenzin Gyatso, is reportedly still in good health, he is now 85 and questions over his succession are growing, along with fears that his death could spark a religious crisis in Asia.

After an unsuccessful revolt against the Chinese occupation of Tibet in 1959, the Dalai Lama fled to India where he established a government-in-exile in Dharamsala, leading thousands of Tibetans who have followed him there. While the Dalai Lama had originally hoped his exile would only be temporary, Beijing's control of Tibet has only tightened, making a return unlikely anytime soon.

© Noah Seelam/AFP/Getty Images A Tibetan activist lights a candle in front of a poster of spirtual leader The Dalai Lama as members of the Regional Tibetan Youth Congress (RTYC) take part in a candlelight vigil during a protest rally in Hyderabad on March 10, 2016.

Today, Beijing views him as a separatist with the aim of breaking Tibet away from China, and is therefore keen for the next reincarnation of his role to fall in line with its own political aims.

Since 1974, the Dalai Lama has said he does not seek independence from China for Tibet, but a "meaningful autonomy" that would allow Tibet to preserve its culture and heritage.

Over the years, the Dalai Lama has floated a number of options for his reincarnation, including picking a new successor himself in India, rather than in Tibet -- and has even toyed with the idea of a woman taking on the role.

Experts, however, have said that, regardless of what he chooses, the Chinese government will almost certainly move to pick a new Dalai Lama in Tibet -- one who is expected to support the ruling Chinese Communist Party's (CCP) control of the region.

That could lead to two separate Dalai Lamas being chosen -- one in China and one in India.

Tenzin Tseten, a research fellow at the Dharamsala-based Tibet Policy Institute, said the Dalai Lama was of great significance to the Tibetan people and a symbol of their "nationalism and identity." "The Tibetan people will never accept a CCP-appointed Dalai Lama," Tenzin said.


History of the Dalai Lama

The Dalai Lama has been reincarnated 13 times since 1391, when the first of his incarnates was born, and normally a centuries-old method is used to find the new leader.

The search begins when the previous Dalai Lama passes away. Sometimes it is based on signs that the former incarnation gave before he died, at other times top lamas -- a monk or priest of varying seniority who teaches Buddhism -- will go to a sacred lake in Tibet, Lhamo Lhatso, and meditate until they have a vision of where to search for his successor.

Then they send out search parties across Tibet, looking for children who are "special" and born within a year of the Dalai Lama's death, according to Ruth Gamble, an expert in Tibetan religion at La Trobe University in Melbourne, Australia.

"There's a heavy responsibility on these people to get it right," she said.

Once they find a number of candidates, the children are tested to determine whether they are the reincarnation of the Dalai Lama. Some of the methods include showing the children items which belong to the previous incarnation.

According to the 14th Dalai Lama's official biography, he was discovered when he was two years old. The son of a farmer, the Dalai Lama was born in a small hamlet in northeastern Tibet, where just 20 families struggled to make a living from the land.

As a child, he recognized a senior lama who had disguised himself to observe the local children, and successfully identified a number of items belonging to the 13th Dalai Lama.

In his autobiography, "My Land and My People," the Dalai Lama wrote that he was handed sets of identical or similar items -- including rosaries, walking sticks and drums -- one of which had belonged to the previous incarnation and one which was ordinary. In every case, he chose the correct one.

But the Dalai Lama's reincarnation hasn't always been found in Tibet. The fourth Dalai Lama was found in Mongolia, while the sixth Dalai Lama was discovered in what is currently Arunachal Pradesh, India.

"The most important thing is the centuries old Tibetan reincarnation system is built on people's faith in rebirth," said Tenzin, from the Tibet Policy Institute.


What the Tibetan government-in-exile might do

At the moment, there are no official instructions laying out how the Dalai Lama's reincarnation will take place, if he dies before returning to Tibet.

But in that significant 2011 statement, the 14th Dalai Lama said that "the person who reincarnates has sole legitimate authority over where and how he or she takes rebirth and how that reincarnation is to be recognized."

The Dalai Lama added that if he chose to reincarnate, the responsibility for finding the 15th Dalai Lama will rest on the Gaden Phodrang Trust, a India-based group he founded after going into exile to preserve and promote Tibetan culture and support the Tibetan people.

The Dalai Lama said that his reincarnation should be carried out "in accordance with past tradition." "I shall leave clear written instructions about this," he said in 2011. CNN reached out to the Gaden Phodrang Trust to see if new instructions had been issued but did not receive a reply.

One thing that has become increasingly clear is that the reincarnation is unlikely to take place in Tibet, an area the Gaden Phodrang Trust cannot even access -- especially after the contested reincarnation of the Panchen Lama in the 1990s.

Following the 1989 death of the 10th Panchen Lama, the second most important figure in Tibetan Buddhism, the Dalai Lama named Tibetan child Gedhun Choekyi Nyima as his colleague's reincarnation.

Gamble, from La Trobe University, said that during the selection process, the Tibetan government-in-exile was secretly in contact with people in Tibet which allowed it to find the reincarnation in a traditional manner.

But three days after he was chosen, according to the US government, Gedhun and his family were disappeared by the CCP, which then appointed an alternative Panchen Lama. Gedhun hasn't been seen in public since.

What the Tibetans-in-exile learned from that experience, said Gamble, is "if you recognize someone inside the PRC and they're really high level, they won't be able to get them out."


What the Chinese government will do

The Chinese government has very publicly telegraphed its intentions for the Dalai Lama's reincarnation -- it will take place in Tibet and it will be in accordance with Beijing's wishes.

In 2007, the Chinese government's State Religious Affairs Bureau published a document which laid out "management measures" for the reincarnation of living Tibetan Buddhas.

The document said that the reincarnations of Tibetan religious figures must be approved by Chinese government authorities, and those with "particularly great impact" must be approved by the State Council, China's top civil administration body currently led by Premier Li Keqiang.

"(Beijing) asserts control over the searches, testing, recognition, education, and training of religious figures," said Tseten, from the Tibet Policy Institute.

There are few specifics about the process of reincarnation in the Chinese government's document, except to recognize the so-called "golden urn" process, which was introduced into Tibet by the Qing Dynasty in the 1790s and sees the names of potential child candidates put into a small golden urn and selected at random.

According to Chinese state-run media, it was put in place to help "eliminate corrupt practices" in the choice of reincarnations.

However, in his 2011 statement, the Dalai Lama said the golden urn was only used to "humor" the Qing emperors, and the reincarnations were already chosen before the names were drawn. The urn was not used in the 14th Dalai Lama's reincarnation.

"Bear in mind that, apart from the reincarnation recognized through such legitimate methods, no recognition or acceptance should be given to a candidate chosen for political ends by anyone, including those in the People's Republic of China," said the Dalai Lama in his statement in 2011.


An authoritative circle

In an update of its Tibetan Policy and Support Act in December 2020, the US threatened to sanction any Chinese government officials who chose a reincarnation of the Dalai Lama over the wishes of the Tibetan people.

But experts said that the CCP has been using a far more insidious method to prepare for the selection of the next Dalai Lama. In recent years, Beijing has been selecting and grooming a group of senior lamas who are friendly to Beijing, according to experts.

When the time comes to select the Dalai Lama's successor, they might make it appear that the Dalai Lama was chosen by Tibetan Buddhist religious leaders, rather than CCP officials.

La Trobe University's Gamble said the reincarnation process has been based on the steady building of religious authority over generations, as one lama recognized another's reincarnation, and then that lama in turn recognized his patron when they returned as a child.

"Their authority lends authority to the next Dalai Lama and then that Dalai Lama gives them back authority by finding them when they're kids and that's what the Chinese government are trying to get themselves involved in, to destabilize that authoritative circle," she said.

Tenzin, from the Tibet Policy Institute, said that Beijing had been slowly raising the profile of their chosen Panchen Lama, who has recently appeared at senior CCP meetings and went on an international visit to Thailand in 2019, to try and build his authority when he selects the 15th Dalai Lama. The Panchan Lama is part of the group of senior lamas who will do the selecting -- another example of this group being groomed and selected by Beijing.

What geopolitical impact the Dalai Lama's death might have on the Tibetans-in-exile is unclear. India has increasingly viewed the community in Dharamsala as a political vulnerability, and some worry that without the Dalai Lama there may be pressure put on the group to leave.

But neither Gamble nor Tenzin, from the Tibet Policy Institute, believed that having two Dalai Lamas would have a huge impact on the legacy of Tenzin Gyatso. "People still keep the photos of the 10th Panchen Lama around as a way of getting around (his reincarnation). They send his teachings and read his books," Gamble said. "I don't think the Dalai Lama's death will end the devotion to him in the way that the CCP thinks it will."

Both experts said they believed that while protests against the CCP's chosen Dalai Lama would be difficult to carry out in Tibet with Beijing keeping a tight grip over the Himalayan region, he would have very little influence over Tibetans compared to his predecessor.

Tenzin said the CCP's treatment of the new Panchen Lama, the second most important figure in Tibetan Buddhism, gives an indication of the pressure the party could apply to any future Dalai Lama -- whether Beijing selects him or not.

According to international advocacy group Human Rights Watch, the current Panchen Lama effectively lives under house arrest in Beijing.

"He is not even able to live in his own monastery," Tenzin said.


CORRECTION: An earlier version of this story misstated the location of the Gaden Phodrang Trust. The group is based in India.