first_imgFor decades, anthropologists have tried to trace the patchy trail left by the earliest modern humans out of Africa. But they have been stymied by gaps in the fossil record or unreliable dates, especially in East Asia. Now, Chinese anthropologists report 47 teeth of Homo sapiens from a cave in southern China, dated to 80,000 to 120,000 years ago. If the dating is accurate, the discovery pushes back the appearance of our species in Asia by at least 30,000 years, wiping out a long-standing picture in which modern humans swept out of Africa in a single wave 50,000 to 70,000 years ago.“This changes everything. It’s the best evidence we have for modern humans in East Asia this early,” says archaeologist 
Michael Petraglia of the University of Oxford in the United Kingdom, who was not part of the work but has long advocated an early migration out of Africa. Others question the dates. “This case is better than the previous similar claims, but it is not fully convincing,” says paleoanthropologist Yousuke Kaifu of the National Museum of Nature and Science in Tokyo.Most researchers agree that modern humans arose in Africa and first ventured out of that continent into the Middle East about 120,000 to 90,000 years ago, as shown by skulls from Israel. But H. sapiens remains don’t appear in Europe, East Asia, and Australia until 40,000 to 50,000 years ago. Older fossils in Asia proposed as H. sapiens are controversial. Genetic studies, too, suggest that humanity’s great global expansion began just 50,000 to 70,000 years ago.Sign up for our daily newsletterGet more great content like this delivered right to you!Country *AfghanistanAland IslandsAlbaniaAlgeriaAndorraAngolaAnguillaAntarcticaAntigua and BarbudaArgentinaArmeniaArubaAustraliaAustriaAzerbaijanBahamasBahrainBangladeshBarbadosBelarusBelgiumBelizeBeninBermudaBhutanBolivia, Plurinational State ofBonaire, Sint Eustatius and SabaBosnia and HerzegovinaBotswanaBouvet IslandBrazilBritish Indian Ocean TerritoryBrunei DarussalamBulgariaBurkina FasoBurundiCambodiaCameroonCanadaCape VerdeCayman IslandsCentral African RepublicChadChileChinaChristmas IslandCocos (Keeling) IslandsColombiaComorosCongoCongo, The Democratic Republic of theCook IslandsCosta RicaCote D’IvoireCroatiaCubaCuraçaoCyprusCzech RepublicDenmarkDjiboutiDominicaDominican RepublicEcuadorEgyptEl SalvadorEquatorial GuineaEritreaEstoniaEthiopiaFalkland Islands (Malvinas)Faroe IslandsFijiFinlandFranceFrench GuianaFrench PolynesiaFrench Southern TerritoriesGabonGambiaGeorgiaGermanyGhanaGibraltarGreeceGreenlandGrenadaGuadeloupeGuatemalaGuernseyGuineaGuinea-BissauGuyanaHaitiHeard Island and Mcdonald IslandsHoly See (Vatican City State)HondurasHong KongHungaryIcelandIndiaIndonesiaIran, Islamic Republic ofIraqIrelandIsle of ManIsraelItalyJamaicaJapanJerseyJordanKazakhstanKenyaKiribatiKorea, Democratic People’s Republic ofKorea, Republic ofKuwaitKyrgyzstanLao People’s Democratic RepublicLatviaLebanonLesothoLiberiaLibyan Arab JamahiriyaLiechtensteinLithuaniaLuxembourgMacaoMacedonia, The Former Yugoslav Republic ofMadagascarMalawiMalaysiaMaldivesMaliMaltaMartiniqueMauritaniaMauritiusMayotteMexicoMoldova, Republic ofMonacoMongoliaMontenegroMontserratMoroccoMozambiqueMyanmarNamibiaNauruNepalNetherlandsNew CaledoniaNew ZealandNicaraguaNigerNigeriaNiueNorfolk IslandNorwayOmanPakistanPalestinianPanamaPapua New GuineaParaguayPeruPhilippinesPitcairnPolandPortugalQatarReunionRomaniaRussian FederationRWANDASaint Barthélemy Saint Helena, Ascension and Tristan da CunhaSaint Kitts and NevisSaint LuciaSaint Martin (French part)Saint Pierre and MiquelonSaint Vincent and the GrenadinesSamoaSan MarinoSao Tome and PrincipeSaudi ArabiaSenegalSerbiaSeychellesSierra LeoneSingaporeSint Maarten (Dutch part)SlovakiaSloveniaSolomon IslandsSomaliaSouth AfricaSouth Georgia and the South Sandwich IslandsSouth SudanSpainSri LankaSudanSurinameSvalbard and Jan MayenSwazilandSwedenSwitzerlandSyrian Arab RepublicTaiwanTajikistanTanzania, United Republic ofThailandTimor-LesteTogoTokelauTongaTrinidad and TobagoTunisiaTurkeyTurkmenistanTurks and Caicos IslandsTuvaluUgandaUkraineUnited Arab EmiratesUnited KingdomUnited StatesUruguayUzbekistanVanuatuVenezuela, Bolivarian Republic ofVietnamVirgin Islands, BritishWallis and FutunaWestern SaharaYemenZambiaZimbabweI also wish to receive emails from AAAS/Science and Science advertisers, including information on products, services and special offers which may include but are not limited to news, careers information & upcoming events.Required fields are included by an asterisk(*)But Petraglia and others have unearthed sophisticated stone tools from the Arabian Peninsula and India, persuading him that modern humans left Africa as long ago as 125,000 years, settled in a then-wet Arabia, then pushed into India and eastward (Science, 29 August 2014, p. 994). Skeptics counter that other archaic humans could have made the tools, and that fossils are needed as proof.Hence the excitement about the teeth reported this week in Nature, from Fuyan Cave in Daoxian in southern China, about 600 kilometers northwest of Hong Kong. A team led by Wu Liu and Xiu-Jie Wu of the Chinese Academy of Sciences’ Institute of Vertebrate Paleontology and Paleoanthropology in Beijing found small teeth with slender roots that barely differed from modern Chinese teeth. Indeed, the wear pattern and shape of the teeth are so modern that some wonder how they could be so old.The dates come from a small stalagmite, part of a flowstone that capped the layer holding the teeth. The team used the radioactive decay of uranium to thorium to date this stalagmite to 80,000 years ago—a minimum age for the teeth. Fossils of extinct elephants, hyenas, and pandas in the hominin layer are 120,000 years old at most, so the team concluded that the teeth are 80,000 to 120,000 years old, says co-author Maria Martinón-Torres of University College London.But the dated stalagmite came from a different trench than the teeth, and may be of a different age, says paleoanthropologist Russell  Ciochon of the University of Iowa in Iowa City: “The actual dates reported for Fuyan Cave are probably good but I doubt that the teeth are that old.”The authors insist that the stratigraphy in the cave is clear. Liu even argues that the find supports the radical—and minority—view that our species was born in China, not Africa. The discovery is likely to spur “a lot of debate,” Martinón-Torres says, “and force a new look at other alleged [H. sapiens] sites in China.”last_img read more

first_imgWhen did life on Earth begin? Scientists have dug down through the geologic record, and the deeper they look, the more it seems that biology appeared early in our planet’s 4.5-billion-year history. So far, geologists have uncovered possible traces of life as far back as 3.8 billion years. Now, a controversial new study presents potential evidence that life arose 300 million years before that, during the mysterious period following Earth’s formation.The clues lie hidden in microscopic flecks of graphite—a carbon mineral—trapped inside a single large crystal of zircon. Zircons grow in magmas, often incorporating other minerals into their crystal structures of silicon, oxygen, and zirconium. And although they barely span the width of a human hair, zircons are nearly indestructible. They can outlast the rocks in which they initially formed, enduring multiple cycles of erosion and deposition.In fact, although the oldest rocks on Earth date back only 4 billion years, researchers have found zircons up to 4.4 billion years old. These crystals provide a rare glimpse into the first chapter of Earth’s history, known as the Hadean eon. “They are pretty much our only physical samples of what was going on on the Earth before 4 billion years ago,” says Elizabeth Bell, a geochemist at the University of California, Los Angeles (UCLA), and lead author of the new study, published online today in the Proceedings of the National Academy of Sciences.Sign up for our daily newsletterGet more great content like this delivered right to you!Country *AfghanistanAland IslandsAlbaniaAlgeriaAndorraAngolaAnguillaAntarcticaAntigua and BarbudaArgentinaArmeniaArubaAustraliaAustriaAzerbaijanBahamasBahrainBangladeshBarbadosBelarusBelgiumBelizeBeninBermudaBhutanBolivia, Plurinational State ofBonaire, Sint Eustatius and SabaBosnia and HerzegovinaBotswanaBouvet IslandBrazilBritish Indian Ocean TerritoryBrunei DarussalamBulgariaBurkina FasoBurundiCambodiaCameroonCanadaCape VerdeCayman IslandsCentral African RepublicChadChileChinaChristmas IslandCocos (Keeling) IslandsColombiaComorosCongoCongo, The Democratic Republic of theCook IslandsCosta RicaCote D’IvoireCroatiaCubaCuraçaoCyprusCzech RepublicDenmarkDjiboutiDominicaDominican RepublicEcuadorEgyptEl SalvadorEquatorial GuineaEritreaEstoniaEthiopiaFalkland Islands (Malvinas)Faroe IslandsFijiFinlandFranceFrench GuianaFrench PolynesiaFrench Southern TerritoriesGabonGambiaGeorgiaGermanyGhanaGibraltarGreeceGreenlandGrenadaGuadeloupeGuatemalaGuernseyGuineaGuinea-BissauGuyanaHaitiHeard Island and Mcdonald IslandsHoly See (Vatican City State)HondurasHong KongHungaryIcelandIndiaIndonesiaIran, Islamic Republic ofIraqIrelandIsle of ManIsraelItalyJamaicaJapanJerseyJordanKazakhstanKenyaKiribatiKorea, Democratic People’s Republic ofKorea, Republic ofKuwaitKyrgyzstanLao People’s Democratic RepublicLatviaLebanonLesothoLiberiaLibyan Arab JamahiriyaLiechtensteinLithuaniaLuxembourgMacaoMacedonia, The Former Yugoslav Republic ofMadagascarMalawiMalaysiaMaldivesMaliMaltaMartiniqueMauritaniaMauritiusMayotteMexicoMoldova, Republic ofMonacoMongoliaMontenegroMontserratMoroccoMozambiqueMyanmarNamibiaNauruNepalNetherlandsNew CaledoniaNew ZealandNicaraguaNigerNigeriaNiueNorfolk IslandNorwayOmanPakistanPalestinianPanamaPapua New GuineaParaguayPeruPhilippinesPitcairnPolandPortugalQatarReunionRomaniaRussian FederationRWANDASaint Barthélemy Saint Helena, Ascension and Tristan da CunhaSaint Kitts and NevisSaint LuciaSaint Martin (French part)Saint Pierre and MiquelonSaint Vincent and the GrenadinesSamoaSan MarinoSao Tome and PrincipeSaudi ArabiaSenegalSerbiaSeychellesSierra LeoneSingaporeSint Maarten (Dutch part)SlovakiaSloveniaSolomon IslandsSomaliaSouth AfricaSouth Georgia and the South Sandwich IslandsSouth SudanSpainSri LankaSudanSurinameSvalbard and Jan MayenSwazilandSwedenSwitzerlandSyrian Arab RepublicTaiwanTajikistanTanzania, United Republic ofThailandTimor-LesteTogoTokelauTongaTrinidad and TobagoTunisiaTurkeyTurkmenistanTurks and Caicos IslandsTuvaluUgandaUkraineUnited Arab EmiratesUnited KingdomUnited StatesUruguayUzbekistanVanuatuVenezuela, Bolivarian Republic ofVietnamVirgin Islands, BritishWallis and FutunaWestern SaharaYemenZambiaZimbabweI also wish to receive emails from AAAS/Science and Science advertisers, including information on products, services and special offers which may include but are not limited to news, careers information & upcoming events.Required fields are included by an asterisk(*)In the study, Bell and her colleagues examined zircons from the Jack Hills in Western Australia, a site that has yielded more Hadean samples than anywhere else on Earth, searching for inclusions of carbon minerals like diamonds and graphite. The mere presence of these minerals does not prove biology existed when the zircons formed, but it does provide the opportunity to look for chemical signs of life. The team eventually found small bits of potentially undisturbed graphite in one 4.1 billion-year-old crystal. The graphite has a low ratio of heavy to light carbon atoms—called isotopes—consistent with the isotopic signature of organic matter. “On Earth today, if you were looking at this carbon, you would say it was biogenic,” Bell says. “Of course, that’s more controversial for the Hadean.”The authors list several nonbiological processes that could explain their findings, but they favor the idea that the graphite started out as organic matter in sediments that got dragged into the Earth’s mantle during the collision of tectonic plates. As the sediments melted to form magma, the elevated temperatures and pressures transformed the carbon into graphite, which eventually found its way into a zircon crystal.If this story is true, and life existed 4.1 billion years ago, Bell says that the new results would corroborate growing evidence of a more hospitable early Earth than scientists once imagined. “The traditional view of the Earth’s first few hundred million years was that this was a sterile, lifeless, hot planet that was constantly being bombarded by meteorites,” she says. But partly thanks to the wealth of information revealed by the Jack Hills zircons in recent years, scientists have come to see the early Earth as much milder and more amenable to life.“We know there was liquid water,” says Mark van Zuilen, a geomicrobiologist at the Paris Institute of Earth Physics. “There’s nothing that holds us back from assuming life was there.” However, van Zuilen and others say they’re not sure the new study provides compelling evidence that it was.Some of this circumspection has roots in recent history. In 2008, researchers announced that diamond-graphite inclusions in 4.3-billion-year-old zircons had potentially biological signatures, inspiring Bell and her team to start looking through UCLA’s own collection of Jack Hills crystals. But subsequent analysis showed the 2008 inclusions came from lab contamination, not early Earth. In the new study, the researchers took measures to prevent similar problems.“That one negative experience doesn’t mean nobody should try again,” says John Eiler, a geologist at the California Institute of Technology in Pasadena. “But let’s just say, I’m cautious.” For one, he says, researchers need to settle some important debates, like whether the inclusions in Hadean zircons truly preserve original material, or if they’ve been altered, for example, during a later bout of metamorphism. He also questions whether organic matter can survive in magma chambers long enough to form graphite, casting doubt on the proposed mechanism.Those issues aside, most scientists—including the authors—agree that the data do not yet exclude nonbiological explanations. Many abiotic processes can produce carbon with isotopic signatures similar to organic matter. For instance, the graphite could contain carbon from certain kinds of meteorites, which have light isotopic compositions. Alternatively, some invoke chemical processes, like the so-called Fischer-Tropsch reactions, in which carbon, oxygen, and hydrogen react with a catalyst like iron to form methane and other hydrocarbons. Such reactions probably occurred near hydrothermal vents in the Hadean, van Zuilen says, and can impart isotopic signatures that are indistinguishable from biological materials.One way to settle the question that doesn’t rely on isotopes involves studying Mars, which, unlike Earth, still has rocks older than 4 billion years on its surface. “If we can find evidence for the existence of life on Mars at that time, then it will be easier to argue the case that it was also present on Earth,” says Alexander Nemchin, a geochemist at Curtin University in Bentley, Australia, and lead author of the 2008 study on diamond inclusions.For now, scientists must make do with zircons, the only materials that preserve any record—however cryptic—of the Hadean eon. Bell acknowledges the need to test her team’s hypothesis on additional samples. She says researchers must make a concerted effort to find more Hadean carbon in Jack Hills zircons and see if it too has potentially biological origins. “Hopefully we didn’t just chance on the one freak zircon that had graphite in it,” she says. “Hopefully there is actually a fair amount of it.”last_img read more

first_imgThe union says the deal, announced on 12 December, is the first of its kind in the world. It also includes an agreement for the union and government departments to work together to develop broader science integrity policies and guidelines. It will include rules to protect government scientists from political interference in their work, and from having their findings manipulated to support a particular political position.The union began pushing for the provision in 2014, in response to the restrictive communications policies of the previous Conservative government led by Prime Minister Stephen Harper. The policies left many researchers feeling they had been muzzled, unable to speak about even the most uncontroversial aspects of their work. A report by the union in 2013 found that 86% of federal scientists felt that they could not publicly share concerns about government policies that could harm public health, safety, or the environment without facing retaliation from their department leaders.The broader scientific community has welcomed the deal, says Kathleen Walsh, executive director of the scientific advocacy group Evidence for Democracy in Ottawa. “It’s a signal of the change in science in Canada in the past year,” she says. Justin Trudeau’s Liberal government, which came to power last year, has reversed many of the Harper government’s communication policies, and stated that federal researchers are free to speak about their work. Scientists working for the Canadian government have successfully negotiated a clause in their new contract that guarantees their right to speak to the public and the media about science and their research, without needing approval from their managers.“Employees shall have the right to express themselves on science and their research, while respecting the Values and Ethics Code for the Public Sector … without being designated as an official media spokesperson,” the new clause states. The ethics code says that while federal employees may talk about their own work, they should not publicly criticize government policy.“This agreement was extremely important in order to ensure that Canadians could trust public science and the decisions that governments make with that science,” says Debi Daviau, president of the Professional Institute of the Public Service of Canada, the Ottawa-based union representing about 15,000 federal scientists. “The Institute is proud to be able to be in a position to ensure that no government will be able to take this away from Canadians again.”Sign up for our daily newsletterGet more great content like this delivered right to you!Country *AfghanistanAland IslandsAlbaniaAlgeriaAndorraAngolaAnguillaAntarcticaAntigua and BarbudaArgentinaArmeniaArubaAustraliaAustriaAzerbaijanBahamasBahrainBangladeshBarbadosBelarusBelgiumBelizeBeninBermudaBhutanBolivia, Plurinational State ofBonaire, Sint Eustatius and SabaBosnia and HerzegovinaBotswanaBouvet IslandBrazilBritish Indian Ocean TerritoryBrunei DarussalamBulgariaBurkina FasoBurundiCambodiaCameroonCanadaCape VerdeCayman IslandsCentral African RepublicChadChileChinaChristmas IslandCocos (Keeling) IslandsColombiaComorosCongoCongo, The Democratic Republic of theCook IslandsCosta RicaCote D’IvoireCroatiaCubaCuraçaoCyprusCzech RepublicDenmarkDjiboutiDominicaDominican RepublicEcuadorEgyptEl SalvadorEquatorial GuineaEritreaEstoniaEthiopiaFalkland Islands (Malvinas)Faroe IslandsFijiFinlandFranceFrench GuianaFrench PolynesiaFrench Southern TerritoriesGabonGambiaGeorgiaGermanyGhanaGibraltarGreeceGreenlandGrenadaGuadeloupeGuatemalaGuernseyGuineaGuinea-BissauGuyanaHaitiHeard Island and Mcdonald IslandsHoly See (Vatican City State)HondurasHong KongHungaryIcelandIndiaIndonesiaIran, Islamic Republic ofIraqIrelandIsle of ManIsraelItalyJamaicaJapanJerseyJordanKazakhstanKenyaKiribatiKorea, Democratic People’s Republic ofKorea, Republic ofKuwaitKyrgyzstanLao People’s Democratic RepublicLatviaLebanonLesothoLiberiaLibyan Arab JamahiriyaLiechtensteinLithuaniaLuxembourgMacaoMacedonia, The Former Yugoslav Republic ofMadagascarMalawiMalaysiaMaldivesMaliMaltaMartiniqueMauritaniaMauritiusMayotteMexicoMoldova, Republic ofMonacoMongoliaMontenegroMontserratMoroccoMozambiqueMyanmarNamibiaNauruNepalNetherlandsNew CaledoniaNew ZealandNicaraguaNigerNigeriaNiueNorfolk IslandNorwayOmanPakistanPalestinianPanamaPapua New GuineaParaguayPeruPhilippinesPitcairnPolandPortugalQatarReunionRomaniaRussian FederationRWANDASaint Barthélemy Saint Helena, Ascension and Tristan da CunhaSaint Kitts and NevisSaint LuciaSaint Martin (French part)Saint Pierre and MiquelonSaint Vincent and the GrenadinesSamoaSan MarinoSao Tome and PrincipeSaudi ArabiaSenegalSerbiaSeychellesSierra LeoneSingaporeSint Maarten (Dutch part)SlovakiaSloveniaSolomon IslandsSomaliaSouth AfricaSouth Georgia and the South Sandwich IslandsSouth SudanSpainSri LankaSudanSurinameSvalbard and Jan MayenSwazilandSwedenSwitzerlandSyrian Arab RepublicTaiwanTajikistanTanzania, United Republic ofThailandTimor-LesteTogoTokelauTongaTrinidad and TobagoTunisiaTurkeyTurkmenistanTurks and Caicos IslandsTuvaluUgandaUkraineUnited Arab EmiratesUnited KingdomUnited StatesUruguayUzbekistanVanuatuVenezuela, Bolivarian Republic ofVietnamVirgin Islands, BritishWallis and FutunaWestern SaharaYemenZambiaZimbabweI also wish to receive emails from AAAS/Science and Science advertisers, including information on products, services and special offers which may include but are not limited to news, careers information & upcoming events.Required fields are included by an asterisk(*)last_img read more

first_img Dr. Chris Berry/Cardiff University By Dennis NormileOct. 23, 2017 , 3:00 PM The world’s first trees grew by splitting their guts Peter Geisen Scientists have discovered some of the best preserved specimens of the world’s first trees in a remote region of China. At up to 12 meters tall, these spindly species were topped by a clump of erect branches vaguely resembling modern palm trees and lived a whopping 393 million to 372 million years ago. But the biggest surprise is how they got so big in the first place.Today’s trees grow through a relatively simple mechanism. The trunk is a single cylindrical shaft made up of hundreds of woody strands called xylem, which conduct water from the roots to the branches and leaves. New xylem grow in rings at the periphery of the trunk just behind the bark, adding girth so the tree can get taller.This is not how ancient trees known as cladoxylopsids grew, however. Two specimens discovered in a desert in China’s northwestern Xinjiang province in 2012 were remarkably well preserved. That’s because they underwent a process in which silica—likely emitted by a nearby volcano—saturated the tree and took on the shape of the wood’s internal structure as it decayed, preserving its 3D cellular structure.Sign up for our daily newsletterGet more great content like this delivered right to you!Country *AfghanistanAland IslandsAlbaniaAlgeriaAndorraAngolaAnguillaAntarcticaAntigua and BarbudaArgentinaArmeniaArubaAustraliaAustriaAzerbaijanBahamasBahrainBangladeshBarbadosBelarusBelgiumBelizeBeninBermudaBhutanBolivia, Plurinational State ofBonaire, Sint Eustatius and SabaBosnia and HerzegovinaBotswanaBouvet IslandBrazilBritish Indian Ocean TerritoryBrunei DarussalamBulgariaBurkina FasoBurundiCambodiaCameroonCanadaCape VerdeCayman IslandsCentral African RepublicChadChileChinaChristmas IslandCocos (Keeling) IslandsColombiaComorosCongoCongo, The Democratic Republic of theCook IslandsCosta RicaCote D’IvoireCroatiaCubaCuraçaoCyprusCzech RepublicDenmarkDjiboutiDominicaDominican RepublicEcuadorEgyptEl SalvadorEquatorial GuineaEritreaEstoniaEthiopiaFalkland Islands (Malvinas)Faroe IslandsFijiFinlandFranceFrench GuianaFrench PolynesiaFrench Southern TerritoriesGabonGambiaGeorgiaGermanyGhanaGibraltarGreeceGreenlandGrenadaGuadeloupeGuatemalaGuernseyGuineaGuinea-BissauGuyanaHaitiHeard Island and Mcdonald IslandsHoly See (Vatican City State)HondurasHong KongHungaryIcelandIndiaIndonesiaIran, Islamic Republic ofIraqIrelandIsle of ManIsraelItalyJamaicaJapanJerseyJordanKazakhstanKenyaKiribatiKorea, Democratic People’s Republic ofKorea, Republic ofKuwaitKyrgyzstanLao People’s Democratic RepublicLatviaLebanonLesothoLiberiaLibyan Arab JamahiriyaLiechtensteinLithuaniaLuxembourgMacaoMacedonia, The Former Yugoslav Republic ofMadagascarMalawiMalaysiaMaldivesMaliMaltaMartiniqueMauritaniaMauritiusMayotteMexicoMoldova, Republic ofMonacoMongoliaMontenegroMontserratMoroccoMozambiqueMyanmarNamibiaNauruNepalNetherlandsNew CaledoniaNew ZealandNicaraguaNigerNigeriaNiueNorfolk IslandNorwayOmanPakistanPalestinianPanamaPapua New GuineaParaguayPeruPhilippinesPitcairnPolandPortugalQatarReunionRomaniaRussian FederationRWANDASaint Barthélemy Saint Helena, Ascension and Tristan da CunhaSaint Kitts and NevisSaint LuciaSaint Martin (French part)Saint Pierre and MiquelonSaint Vincent and the GrenadinesSamoaSan MarinoSao Tome and PrincipeSaudi ArabiaSenegalSerbiaSeychellesSierra LeoneSingaporeSint Maarten (Dutch part)SlovakiaSloveniaSolomon IslandsSomaliaSouth AfricaSouth Georgia and the South Sandwich IslandsSouth SudanSpainSri LankaSudanSurinameSvalbard and Jan MayenSwazilandSwedenSwitzerlandSyrian Arab RepublicTaiwanTajikistanTanzania, United Republic ofThailandTimor-LesteTogoTokelauTongaTrinidad and TobagoTunisiaTurkeyTurkmenistanTurks and Caicos IslandsTuvaluUgandaUkraineUnited Arab EmiratesUnited KingdomUnited StatesUruguayUzbekistanVanuatuVenezuela, Bolivarian Republic ofVietnamVirgin Islands, BritishWallis and FutunaWestern SaharaYemenZambiaZimbabweI also wish to receive emails from AAAS/Science and Science advertisers, including information on products, services and special offers which may include but are not limited to news, careers information & upcoming events.Required fields are included by an asterisk(*)The fossils reveal that, unlike modern trees with a single shaft, cladoxylopsids had multiple xylem columns spaced around the perimeter of a hollow trunk. A network of crisscrossing strands connected the vertical xylem—much like a chain-link fence spreads from pole to pole—and soft tissue filled the spaces between all these strands. New growth formed in rings around each of the xylem columns while an increasing volume of soft tissue forced the strands to spread out.All of this expanded the girth of the trunk, allowing for a taller tree. But it also split apart the tree’s xylem skeleton, which required the tree to continually repair itself, the team reports today in the Proceedings of the National Academy of Sciences. The weight of the tree squeezed tissue at the base of the trunk outward. center_img An artist’s impression of a stand of cladoxylopsida trees, which formed Earth’s first forests. In the largest of the two fossil trunks, above the bulge, the xylem and soft tissue occupied a ring about 50 centimeters in diameter and 5 centimeters thick, with external roots making up the remainder of the 70-centimeter-diameter tree trunk. The scientists estimate cladoxylopsids could have been 8 to 12 meters tall.This growth strategy has not been seen in any other tree in Earth’s history, says Xu Hong-He, a paleontologist at the Nanjing Institute of Geology and Paleontology in China who discovered the fossilized tree trunks. “It’s crazy that the oldest trees also had the most complex growth strategy,” adds Christopher Berry, a plant paleontologist at Cardiff University in the United Kingdom who helped analyze the fossils.The trees are particularly important, says Berry, because they dominated Earth during the Devonian period from 419 million to 358 million years ago. They formed the first forests and played a key role in absorbing carbon dioxide from the atmosphere. They also added oxygen to the atmosphere, affecting the climate and influencing conditions that fostered the emergence of other life forms, he says. Despite their early critical role in the evolution of life on Earth, the cladoxylopsids do not have any modern descendants. They disappeared at the end of the Devonian period, perhaps because they were left in the shade of taller, more robust trees, or because changing environmental conditions may have favored Archaeopteris, the ancestors of modern trees that appeared about 385 million years ago.The new study is an important step in solving several such mysteries about early Earth, says Brigitte Meyer-Berthaud, a paleobotanist at the University of Montpellier in France who was not involved in the research. To understand the role of cladoxylopsids on our planet’s past, she says, “it is essential to know how the trees are constructed.” Fossilized slices of a 374-million-year-old tree reveal a hollow core surrounded by numerous bundles of woody strands called xylem (the larger black spots), with soft tissue (in gray) between. The smaller black dots are roots.last_img read more

first_img Alzheimer’s protein may spread like an infection, human brain scans suggest The average accumulation of tau protein, represented by the red spheres, as visualized during positron emission tomography scans of 17 subjects with Alzheimer’s disease. Thomas Cope For the first time, scientists have produced evidence in living humans that the protein tau, which mars the brain in Alzheimer’s disease, spreads from neuron to neuron. Although such movement wasn’t directly observed, the finding may illuminate how neurodegeneration occurs in the devastating illness, and it could provide new ideas for stemming the brain damage that robs so many of memory and cognition.Tau is one of two proteins—along with β-amyloid—that form unusual clumps in the brains of people with Alzheimer’s disease. Scientists have long debated which is most important to the condition and, thus, the best target for intervention. Tau deposits are found inside neurons, where they are thought to inhibit or kill them, whereas β-amyloid forms plaques outside brain cells.Researchers at the University of Cambridge in the United Kingdom combined two brain imaging techniques, functional magnetic resonance imaging and positron emission tomography (PET) scanning, in 17 Alzheimer’s patients to map both the buildup of tau and their brains’ functional connectivity—that is, how spatially separated brain regions communicate with each other. Strikingly, they found the largest concentrations of the damaging tau protein in brain regions heavily wired to others, suggesting that tau may spread in a way analogous to influenza during an epidemic, when people with the most social contacts will be at greatest risk of catching the disease. Sign up for our daily newsletterGet more great content like this delivered right to you!Country *AfghanistanAland IslandsAlbaniaAlgeriaAndorraAngolaAnguillaAntarcticaAntigua and BarbudaArgentinaArmeniaArubaAustraliaAustriaAzerbaijanBahamasBahrainBangladeshBarbadosBelarusBelgiumBelizeBeninBermudaBhutanBolivia, Plurinational State ofBonaire, Sint Eustatius and SabaBosnia and HerzegovinaBotswanaBouvet IslandBrazilBritish Indian Ocean TerritoryBrunei DarussalamBulgariaBurkina FasoBurundiCambodiaCameroonCanadaCape VerdeCayman IslandsCentral African RepublicChadChileChinaChristmas IslandCocos (Keeling) IslandsColombiaComorosCongoCongo, The Democratic Republic of theCook IslandsCosta RicaCote D’IvoireCroatiaCubaCuraçaoCyprusCzech RepublicDenmarkDjiboutiDominicaDominican RepublicEcuadorEgyptEl SalvadorEquatorial GuineaEritreaEstoniaEthiopiaFalkland Islands (Malvinas)Faroe IslandsFijiFinlandFranceFrench GuianaFrench PolynesiaFrench Southern TerritoriesGabonGambiaGeorgiaGermanyGhanaGibraltarGreeceGreenlandGrenadaGuadeloupeGuatemalaGuernseyGuineaGuinea-BissauGuyanaHaitiHeard Island and Mcdonald IslandsHoly See (Vatican City State)HondurasHong KongHungaryIcelandIndiaIndonesiaIran, Islamic Republic ofIraqIrelandIsle of ManIsraelItalyJamaicaJapanJerseyJordanKazakhstanKenyaKiribatiKorea, Democratic People’s Republic ofKorea, Republic ofKuwaitKyrgyzstanLao People’s Democratic RepublicLatviaLebanonLesothoLiberiaLibyan Arab JamahiriyaLiechtensteinLithuaniaLuxembourgMacaoMacedonia, The Former Yugoslav Republic ofMadagascarMalawiMalaysiaMaldivesMaliMaltaMartiniqueMauritaniaMauritiusMayotteMexicoMoldova, Republic ofMonacoMongoliaMontenegroMontserratMoroccoMozambiqueMyanmarNamibiaNauruNepalNetherlandsNew CaledoniaNew ZealandNicaraguaNigerNigeriaNiueNorfolk IslandNorwayOmanPakistanPalestinianPanamaPapua New GuineaParaguayPeruPhilippinesPitcairnPolandPortugalQatarReunionRomaniaRussian FederationRWANDASaint Barthélemy Saint Helena, Ascension and Tristan da CunhaSaint Kitts and NevisSaint LuciaSaint Martin (French part)Saint Pierre and MiquelonSaint Vincent and the GrenadinesSamoaSan MarinoSao Tome and PrincipeSaudi ArabiaSenegalSerbiaSeychellesSierra LeoneSingaporeSint Maarten (Dutch part)SlovakiaSloveniaSolomon IslandsSomaliaSouth AfricaSouth Georgia and the South Sandwich IslandsSouth SudanSpainSri LankaSudanSurinameSvalbard and Jan MayenSwazilandSwedenSwitzerlandSyrian Arab RepublicTaiwanTajikistanTanzania, United Republic ofThailandTimor-LesteTogoTokelauTongaTrinidad and TobagoTunisiaTurkeyTurkmenistanTurks and Caicos IslandsTuvaluUgandaUkraineUnited Arab EmiratesUnited KingdomUnited StatesUruguayUzbekistanVanuatuVenezuela, Bolivarian Republic ofVietnamVirgin Islands, BritishWallis and FutunaWestern SaharaYemenZambiaZimbabweI also wish to receive emails from AAAS/Science and Science advertisers, including information on products, services and special offers which may include but are not limited to news, careers information & upcoming events.Required fields are included by an asterisk(*)The research team says this pattern, described yesterday in Brain, supports something known as the “transneuronal spread” hypothesis for Alzheimer’s disease, which had previously been demonstrated in mice but not people. “We come down quite strongly in favor of the idea that tau is starting in one place and moving across neurons and synapses to other places,” says clinical neurologist Thomas Cope, one of the study’s authors. “That has never before been shown in humans. That’s very exciting.” Because the researchers looked at Alzheimer’s patients with a range of disease severity, they were also able to demonstrate that, when tau accumulation was higher, brain regions were on the whole less connected. The strength of connections also decreased, and connections were increasingly random.Nathan Spreng, a neuroscientist who studies brain networks and Alzheimer’s disease at the Montreal Neurological Institute and Hospital in Canada, calls the evidence for an infectionlike spread of tau “fascinating and compelling.” But others note that the study did not follow patients across time, a big weakness that makes it difficult to conclude that “tau spreading” caused the decreased functional connectivity, says Jorge Sepulcre of Harvard Medical School in Boston, who uses PET scanning to probe the impacts of neurodegenerative diseases on brain network connectivity. “The study’s conclusions should be taken cautiously as they do not include longitudinal proof or validation about the spreading nature of tau,” he says.Yet the global picture of deterioration in the study makes it valuable, Spreng says. “While animal work has looked at how [tau] spread happens from synapse to synapse, this study shows nicely what the brain-wide effects are as the networks start to degenerate in the context of progressive Alzheimer’s disease.” He notes, however, that the small sample size is a concern.Although he’s confident his team has already demonstrated the transneuronal spread of tau, Cope says that the Cambridge group is now following larger numbers of subjects with Alzheimer’s and tracking individuals across time with brain imaging. The spread of tau could have implications for clinical care, he adds, if drugs can be developed that attack tau in synapses, outside of cells, locking it up inside affected cells early, before it can spread. By Meredith WadmanJan. 5, 2018 , 2:05 PMlast_img read more

first_imgA scanning electron microscopy image of the wood-cutting mandibles of a young Melissotarsus worker. Evolution turned this ant into a living drill A. Khalife et al., Frontiers in Zoology 10.1186 (2018) Artist’s conception of a Melissotarsus worker boring a tunnel. While tunneling, these ants brace themselves against the tunnel walls using strong, specialized legs and basitarsi “heels” to anchor themselves in place. Even the jaw opening muscles are stronger than those of any species of ant known, a characteristic Peeters thinks may be useful in pushing wood debris out of the way while tunneling.The researchers also found that the mandibles themselves were remarkably well-suited to a life of chewing. Their wide base made them efficient levers, and analysis of their tips revealed high concentrations of zinc embedded within the exoskeleton.Zinc-reinforced “heavy element biomaterials” like these are common in invertebrates, says Robert Schofield, a biophysicist at the University of Oregon in Eugene who was not involved in the study. They’re found in body parts that sustain heavy use, such as spider fangs and marine worm jaws. The nanoscale clusters of zinc are bound into the chitin matrix, imparting hardness without increasing the risk of breakage. For ants that depend on these tools to build and eat with, that’s pretty important. “If a sharp tip gets damaged, then they’re dead,” Schofield says.The legs of Melissotarsus workers are also superbly adapted. The researchers found that the legs—perpetually bent close to the body—have strong muscles for bracing against tunnel walls. The “basitarsus” of the ants’ feet (analogous to a heel) is also enlarged, and—with the addition of peglike bristles—provides extra grip when bearing down. This keeps workers rigidly anchored in place, counteracting the intense chewing forces. But the adaptations come with a cost: The ants’ legs are so dramatically modified that the insects can no longer walk on a flat surface (see video, below). By Jake BuehlerAug. 24, 2018 , 9:55 AM A. Khalife et al., Frontiers in Zoology 10.1186 (2018) Anyone who’s attempted to cut down a tree by hand knows just how difficult it is to chop through living wood. It turns out wood-boring ants do, too—so they’ve transformed themselves into bizarre, living drills. A new study reveals that extreme adaptations unlike anything seen in other ants let them carve complicated tunnel networks in their host trees.Not much is known about Melissotarsus ants—native to continental Africa and Madagascar—because they’re only a few millimeters long and never leave the carved galleries of their trees. Inside, the ants are thought to herd sedentary scale insects for food, eating their tasty wax secretions or even their meat. Worker ants have two pairs of back legs that perpetually angle upward and a bulbous head loaded with silk glands (a unique feature among ants). Entomologists have long thought these features must assist with the ants’ unconventional lifestyle, but they weren’t sure exactly how.“It was not obvious how they could derive the strength to chew live wood,” says Christian Peeters, a research biologist at Sorbonne University in Paris and senior author on the study.Sign up for our daily newsletterGet more great content like this delivered right to you!Country *AfghanistanAland IslandsAlbaniaAlgeriaAndorraAngolaAnguillaAntarcticaAntigua and BarbudaArgentinaArmeniaArubaAustraliaAustriaAzerbaijanBahamasBahrainBangladeshBarbadosBelarusBelgiumBelizeBeninBermudaBhutanBolivia, Plurinational State ofBonaire, Sint Eustatius and SabaBosnia and HerzegovinaBotswanaBouvet IslandBrazilBritish Indian Ocean TerritoryBrunei DarussalamBulgariaBurkina FasoBurundiCambodiaCameroonCanadaCape VerdeCayman IslandsCentral African RepublicChadChileChinaChristmas IslandCocos (Keeling) IslandsColombiaComorosCongoCongo, The Democratic Republic of theCook IslandsCosta RicaCote D’IvoireCroatiaCubaCuraçaoCyprusCzech RepublicDenmarkDjiboutiDominicaDominican RepublicEcuadorEgyptEl SalvadorEquatorial GuineaEritreaEstoniaEthiopiaFalkland Islands (Malvinas)Faroe IslandsFijiFinlandFranceFrench GuianaFrench PolynesiaFrench Southern TerritoriesGabonGambiaGeorgiaGermanyGhanaGibraltarGreeceGreenlandGrenadaGuadeloupeGuatemalaGuernseyGuineaGuinea-BissauGuyanaHaitiHeard Island and Mcdonald IslandsHoly See (Vatican City State)HondurasHong KongHungaryIcelandIndiaIndonesiaIran, Islamic Republic ofIraqIrelandIsle of ManIsraelItalyJamaicaJapanJerseyJordanKazakhstanKenyaKiribatiKorea, Democratic People’s Republic ofKorea, Republic ofKuwaitKyrgyzstanLao People’s Democratic RepublicLatviaLebanonLesothoLiberiaLibyan Arab JamahiriyaLiechtensteinLithuaniaLuxembourgMacaoMacedonia, The Former Yugoslav Republic ofMadagascarMalawiMalaysiaMaldivesMaliMaltaMartiniqueMauritaniaMauritiusMayotteMexicoMoldova, Republic ofMonacoMongoliaMontenegroMontserratMoroccoMozambiqueMyanmarNamibiaNauruNepalNetherlandsNew CaledoniaNew ZealandNicaraguaNigerNigeriaNiueNorfolk IslandNorwayOmanPakistanPalestinianPanamaPapua New GuineaParaguayPeruPhilippinesPitcairnPolandPortugalQatarReunionRomaniaRussian FederationRWANDASaint Barthélemy Saint Helena, Ascension and Tristan da CunhaSaint Kitts and NevisSaint LuciaSaint Martin (French part)Saint Pierre and MiquelonSaint Vincent and the GrenadinesSamoaSan MarinoSao Tome and PrincipeSaudi ArabiaSenegalSerbiaSeychellesSierra LeoneSingaporeSint Maarten (Dutch part)SlovakiaSloveniaSolomon IslandsSomaliaSouth AfricaSouth Georgia and the South Sandwich IslandsSouth SudanSpainSri LankaSudanSurinameSvalbard and Jan MayenSwazilandSwedenSwitzerlandSyrian Arab RepublicTaiwanTajikistanTanzania, United Republic ofThailandTimor-LesteTogoTokelauTongaTrinidad and TobagoTunisiaTurkeyTurkmenistanTurks and Caicos IslandsTuvaluUgandaUkraineUnited Arab EmiratesUnited KingdomUnited StatesUruguayUzbekistanVanuatuVenezuela, Bolivarian Republic ofVietnamVirgin Islands, BritishWallis and FutunaWestern SaharaYemenZambiaZimbabweI also wish to receive emails from AAAS/Science and Science advertisers, including information on products, services and special offers which may include but are not limited to news, careers information & upcoming events.Required fields are included by an asterisk(*)So Peeters and his team took a closer look. The researchers removed ant-inhabited branches from trees in Mozambique and South Africa, sending them back to the lab in Paris. There they combined x-ray microtomography (a type of 3D x-ray imaging for tiny objects) and high-powered microscopes to visualize the ants’ skeletomuscular system, focusing on the anatomy of the head, jaws, and legs.It turns out that their big domes house more than just silk glands—huge muscles fill the head, anchored to short, sharp mandibles, the team reports in Frontiers in Zoology. These muscles provide the jaws with enormous chiseling power that can tunnel through hardwood. In contrast, ants with weaker jaws typically have to make do with settling in rotten wood or tunnels already excavated by boring beetles. That’s because chewing dry wood—whose fibers are brittle and easily broken—is easier than chewing through healthy, moist wood, Peeters explains. “This is a great paper on an amazing ant,” says Andy Suarez, an entomologist at the University of Illinois in Urbana, who was not involved in the study. “This is the only example I know of where an ant has evolved a lifestyle … living in [the] wood of living trees that requires workers to be able to tunnel through the wood itself.”Melissotarsus has evolved an “irreversible commitment” to life inside the trees, Peeters says, forsaking the outside world to tend to their scale insect herds. The findings illustrate the extraordinary results that evolutionary specialization can produce, turning once highly mobile ants into tireless power tools.last_img read more

first_img NASA/JPL-CALTECH An asteroid collision 466 million years ago created meteorites that still fall to Earth. Veil of dust from ancient asteroid breakup may have cooled Earth By Joshua SokolSep. 18, 2019 , 2:00 PM Faced with a dangerously warming world, would-be geoengineers have dreamed up ways to quickly turn down the heat. One proposed technique: spreading a veil of dust that would sit in space or Earth’s atmosphere and reflect sunlight. Researchers say they have now found evidence for a similar experiment that played out naturally, 466 million years ago, when an asteroid out in space exploded into bits. Dust from the breakup blanketed the planet, says Birger Schmitz, a geologist at Lund University in Sweden, plunging it into an ice age that was soon followed by an explosion in animal life.The ancient episode offers both encouragement and caution for geoengineers. If Schmitz is right, it dramatically demonstrates how dust can cool the planet. But the deep freeze is a lesson in potential unintended consequences. “Maybe our study will trigger a big academic controversy,” says Schmitz, who leads a study published this week in Science Advances.All over the world, the ratio of decaying isotopes in a common meteorite type suggests the space rocks formed in a singular shock event 466 million years ago. Models based on how long they took to cool suggest they came from a 150-kilometer-wide parent body, which broke up in a collision in the asteroid belt beyond Mars, sending a stream of fragments into the inner solar system. Bits from the breakup still fall to Earth today.Sign up for our daily newsletterGet more great content like this delivered right to you!Country *AfghanistanAland IslandsAlbaniaAlgeriaAndorraAngolaAnguillaAntarcticaAntigua and BarbudaArgentinaArmeniaArubaAustraliaAustriaAzerbaijanBahamasBahrainBangladeshBarbadosBelarusBelgiumBelizeBeninBermudaBhutanBolivia, Plurinational State ofBonaire, Sint Eustatius and SabaBosnia and HerzegovinaBotswanaBouvet IslandBrazilBritish Indian Ocean TerritoryBrunei DarussalamBulgariaBurkina FasoBurundiCambodiaCameroonCanadaCape VerdeCayman IslandsCentral African RepublicChadChileChinaChristmas IslandCocos (Keeling) IslandsColombiaComorosCongoCongo, The Democratic Republic of theCook IslandsCosta RicaCote D’IvoireCroatiaCubaCuraçaoCyprusCzech RepublicDenmarkDjiboutiDominicaDominican RepublicEcuadorEgyptEl SalvadorEquatorial GuineaEritreaEstoniaEthiopiaFalkland Islands (Malvinas)Faroe IslandsFijiFinlandFranceFrench GuianaFrench PolynesiaFrench Southern TerritoriesGabonGambiaGeorgiaGermanyGhanaGibraltarGreeceGreenlandGrenadaGuadeloupeGuatemalaGuernseyGuineaGuinea-BissauGuyanaHaitiHeard Island and Mcdonald IslandsHoly See (Vatican City State)HondurasHong KongHungaryIcelandIndiaIndonesiaIran, Islamic Republic ofIraqIrelandIsle of ManIsraelItalyJamaicaJapanJerseyJordanKazakhstanKenyaKiribatiKorea, Democratic People’s Republic ofKorea, Republic ofKuwaitKyrgyzstanLao People’s Democratic RepublicLatviaLebanonLesothoLiberiaLibyan Arab JamahiriyaLiechtensteinLithuaniaLuxembourgMacaoMacedonia, The Former Yugoslav Republic ofMadagascarMalawiMalaysiaMaldivesMaliMaltaMartiniqueMauritaniaMauritiusMayotteMexicoMoldova, Republic ofMonacoMongoliaMontenegroMontserratMoroccoMozambiqueMyanmarNamibiaNauruNepalNetherlandsNew CaledoniaNew ZealandNicaraguaNigerNigeriaNiueNorfolk IslandNorwayOmanPakistanPalestinianPanamaPapua New GuineaParaguayPeruPhilippinesPitcairnPolandPortugalQatarReunionRomaniaRussian FederationRWANDASaint Barthélemy Saint Helena, Ascension and Tristan da CunhaSaint Kitts and NevisSaint LuciaSaint Martin (French part)Saint Pierre and MiquelonSaint Vincent and the GrenadinesSamoaSan MarinoSao Tome and PrincipeSaudi ArabiaSenegalSerbiaSeychellesSierra LeoneSingaporeSint Maarten (Dutch part)SlovakiaSloveniaSolomon IslandsSomaliaSouth AfricaSouth Georgia and the South Sandwich IslandsSouth SudanSpainSri LankaSudanSurinameSvalbard and Jan MayenSwazilandSwedenSwitzerlandSyrian Arab RepublicTaiwanTajikistanTanzania, United Republic ofThailandTimor-LesteTogoTokelauTongaTrinidad and TobagoTunisiaTurkeyTurkmenistanTurks and Caicos IslandsTuvaluUgandaUkraineUnited Arab EmiratesUnited KingdomUnited StatesUruguayUzbekistanVanuatuVenezuela, Bolivarian Republic ofVietnamVirgin Islands, BritishWallis and FutunaWestern SaharaYemenZambiaZimbabweI also wish to receive emails from AAAS/Science and Science advertisers, including information on products, services and special offers which may include but are not limited to news, careers information & upcoming events.Required fields are included by an asterisk(*)Schmitz’s team has found a rich source of the debris: a limestone quarry in southern Sweden. Since the 1990s, it has yielded more than 100 fossil meteorites, found in rock layers that date to soon after the asteroid breakup. “The flux had to be enormous at this time,” says Bill Bottke, a planetary scientist at the Southwest Research Institute in Boulder, Colorado, who has studied the breakup.The meteorites fell about the time early animal life boomed. Major animal groups had already evolved, but during this Great Ordovician Biodiversification Event (GOBE), ocean animals doubled or even tripled in biodiversity. Reefs built by microbes gave way to some of the first coral reefs, trilobites grew larger, and tentacled predators such as nautiloids diversified and swarmed the mostly fishless seas. In 2008, Schmitz argued that the asteroid breakup might be responsible. Perhaps, he and colleagues proposed, large fragments striking Earth spurred the GOBE by shaking up ecosystems, clearing out ecological niches for new species to evolve into.But the idea didn’t catch on, in part because there was no sign of large impact craters from just after the collision. Instead, some paleontologists offered a different trigger for the GOBE: a succession of ice ages that took place at the same time. Colder water can hold more dissolved oxygen, fueling life. And as water froze into glaciers, sea levels dropped, isolating shallow seas and creating niches for speciation.Schmitz’s team now thinks the asteroid breakup brought on those ice ages, by creating a cloud of dust that hung in space and in the atmosphere, reflecting sunlight away from Earth and allowing the ice to build up. In layers of limestone spanning just a few million years, from the original quarry and other sites in Sweden and Russia, the team found a surge in both small extraterrestrial grains and in chemical isotopes that trace even finer extraterrestrial dust. “All this dust floated in, just when the sea level fall started,” Schmitz says. “Suddenly it clicked.”Rebecca Freeman, a paleontologist at the University of Kentucky in Lexington, says the timing is “perfect.” “It isn’t necessarily the answer to every question, but it certainly ties together a lot of observations,” she says.Peter Reiners, a geochemist at the University of Arizona in Tucson, argues that the falling asteroid dust would have also delivered iron to the world’s oceans, chilling the climate a different way. The dust would have nourished photosynthetic microbes at the sea surface, drawing carbon dioxide out of the atmosphere. When they died and sank, much of the carbon they absorbed would be buried with them, further cooling the planet.The ancient events are eerily similar to modern-day geoengineering schemes. A study in 2012 evaluated the idea of towing an asteroid to a gravitationally stable point between Earth and the sun, and grinding off dust that would remain in space and shade Earth. Researchers found that a 32-kilometer-wide near-Earth asteroid called 1036 Ganymed could make a dust cloud big enough to remain in place and block 6.6% of the sun’s light, well over the 1.7% reduction the authors say could offset 2°C of expected warming. Fertilizing the ocean with iron has also been proposed to combat climate change.Seth Finnegan, a paleontologist at the University of California, Berkeley, is not yet convinced about the ancient geoengineering event. He wants to see global evidence for extraterrestrial dust, alongside signals for cooling and biodiversification. He also urges researchers to model how much dust the asteroid breakup would have made, and how it would have affected climate. Schmitz says he’s searching for dust at a third site in central China.If it turns out that a powdered asteroid really did have such a profound effect on the Ordovician, Finnegan adds, then the episode also delivers a warning: It “shows that the consequences of messing around in that way could be pretty severe.”last_img read more