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News in focus early­stage trial results such as those released emphasis on identifying candidates being and the cave could have provided shelter to this week. But comparisons can be thwarted by developed by companies that are capable any humans who were around to witness the the fickle nature of the tests researchers use of making enough vaccine for much of the blizzards. to measure neutralizing­antibody and T­cell world. That could depend on myriad issues, The team makes a good case for ancient responses. The same test can return widely such as sourcing glass vials and maintain­ human occupation, says François Lanoë, different values when performed in different ing temperature-­controlled supply chains. an archaeologist and anthropologist at the laboratories, or even on different days. “That’s like organizing a Moon landing or a University of Arizona in Tucson. But he adds “It’s hard for us to compare our vaccine world­war invasion,” says Altmann. “Which­ that data from caves are “notoriously trouble­ results to other people’s,” said vaccinologist ever candidates we pick, we want them to be some” to interpret. Stone tools might have Adrian Hill, a co­leader of the Oxford effort, the ones that can most optimize that.” been shifted into deeper layers by geological in the briefing. “We would really like to see or biological activity — perhaps moved by different vaccines being tested in the same 1. Folegatti, P. M. et al. Lancet https://doi.org/10.1016/S0140- burrowing animals — making them seem older 6736(20)31604-4 (2020). lab by the same people.” 2. Zhu, F-C. et al. Lancet https://doi.org/10.1016/S0140- than they really are. Most of the front­runner vaccines 6736(20)31605-6 (2020). That’s assuming they really are stone tools. “could do the trick”, says Daniel Altmann, an 3. Sahin, U. et al. Preprint at MedRxiv https://doi. “If an artefact is a stone tool, you see numerous org/10.1101/2020.07.17.20140533 (2020). immunologist at Imperial College London. 4. Jackson, L. A. et al. N. Engl. J. Med. https://doi. chips removed from the edge,” says Kurt But he worries that there is not enough org/10.1056/NEJMoa2022483 (2020). Rademaker, an archaeologist at Michigan State University in East Lansing. He sees no clear evidence of this in the images in the paper. Ardelean admits that some of the tools might have shifted into lower layers, although he says the 239 oldest ones lie beneath an WHEN DID PEOPLE REACH impenetrable layer of mud formed during the last ice age, so they must be at least that THE AMERICAS? CAVE old. He insists they are tools — in fact, he thinks some have telltale marks suggesting that they TOOLS STOKE DEBATE were made by novices learning from experts. Aside from the stone tools, the team found Stone artefacts point to occupation more than relatively little evidence of humans at the site. Geneticists led by Eske Willerslev at the Uni­ 30,000 years ago — but not everyone is convinced. versity of Copenhagen searched for ancient human DNA in the cave dirt, but with no luck. By Colin Barras Chiquihuite Cave, which is 2,740 metres above sea level in the country’s Astillero Mountains. Early settlers rchaeologists excavating a cave in The researchers found almost 2,000 stone In a second study (L. Becerra­Valdivia and the mountains of central Mexico tools, 239 of which were embedded in layers of T. Higham Nature http://doi.org/gg5s5f; 2020) have unearthed evidence that gravel that have been carbon dated to between two of Ardelean’s co­authors — archaeologists people occupied the area more than 25,000 and 32,000 years ago. Thomas Higham and Lorena Becerra­Valdivia 30,000 years ago — suggesting that Ardelean thinks the site might have been at the University of Oxford, UK — combined Ahumans arrived in North America at least used as a refuge during particularly severe the Chiquihuite Cave evidence with data from 15,000 years earlier than thought. winters. At the height of the last ice age, 41 other sites in North America and a region The discovery, which includes hundreds 26,000 years ago, North America would have of eastern Siberia and western Alaska called of ancient stone tools, is backed up by a been a dangerous place. “There must have Beringia, and built a statistical model of early statistical analysis that incorporates data been horrible storms, hail, snow,” he says, human settlement. They concluded that peo­ from other sites. But the conclusion has stirred ple were present across North America much controversy among some researchers. earlier than the accepted date of 15,000– The first humans in the Americas came 16,000 years ago. from East Asia, but when they began to arrive Some archaeologists think that it is time is hotly debated. Some researchers think that to take these ideas seriously. “The growing it could have been as early as 130,000 years body of evidence for people in Beringia before ago, although most of the archaeological evi­ 15,000 years ago renders their appearance in dence supporting this theory is disputed. For places like Mexico 20,000 or 30,000 years instance, some of the stone artefacts are so ago less surprising,” says John Hoffecker, an simple that sceptics say they were probably archaeologist at the University of Colorado produced by natural geological processes Boulder. rather than by people. The mainstream view is Others disagree. Collins says Becerra-­ that the peopling of the Americas began about Valdivia and Higham assume that early sites 15,000 or 16,000 years ago — based on genetic such as Chiquihuite Cave offer unambiguous evidence and artefacts found at sites including evidence of human activity. “This is far from the 14,000­year­old Monte Verde II in Chile. the case,” he says. The latest discoveries (C. F. Ardelean et al. Becerra­Valdivia accepts that evidence Nature http://doi.org/d4wz; 2020) question from most sites — except Monte Verde II that consensus. Since 2012, a team led by — is disputed, but says that the analysis MADS THOMSEN Ciprian Ardelean at the Autonomous Univer­ Excavations in Chiquihuite Cave, Mexico. purposely omitted information from the most sity of Zacatecas in Mexico has been excavating controversial sites, to make its case stronger. 670 | Nature | Vol 583 | 30 July 2020 ©2020 Spri nger Nature Li mited. All rights reserved. ©2020 Spri nger Nature Li mited. All rights reserved. If there were people in North America so Ardelean says there is a simple reason why Together with the success of the UAE’s early, it’s unclear what happened to them. genetic studies suggest that humans spread orbiter, Tianwen­1 adds weight to a new “There continues to be no convincing genetic across the Americas only relatively recently: reality, “that Solar System exploration is not the evidence of a pre­15,000­years­ago human early groups such as the one he thinks was prerogative of the Euro­American world, but a presence in the Americas,” says geneticist present at Chiquihuite Cave didn’t survive to global enterprise”, says geologist Jon Clarke, David Reich at Harvard Medical School in contribute to modern gene pools. “I definitely who is president of the Mars Society Australia Boston, Massachusetts. advocate for the idea of lost groups,” he says. based in Canberra. China, India and Japan have previously sent probes into space, including missions to the Moon, Mars, Venus and some asteroids. Tianwen­1 is now coasting through space before it reaches its destination in February. CHINA’S MARS LAUNCH The craft will then spend several months positioning itself for the landing. In April, the SEALS NEW ERA IN orbiter will release the lander and rover into the Martian atmosphere, and these will touch DEEP-SPACE EXPLORATION down somewhere on Utopia Planitia — a vast plain littered with volcanic rocks, within a large The Tianwen­1 mission represents the country’s basin. If the landing is successful, China will be only the second country, after the United first attempt to land on the red planet. States, to softly land a rover on Mars, says Flannery. The six­wheeled, solar­powered rover, which has a lifetime of around 90 Mar­ tian days — the equivalent of some 93 days on Earth — will explore areas of scientific interest. The orbiter will loop around Mars for an entire Martian year — 687 Earth days. China’s mission aims to conduct a global survey of the planet, including studying its geological structures, surface characteris­ tics and climate. The orbiter is packed with seven scientific instruments, and the rover has six more. These include several cameras, subsurface radar and a spectrometer. A magnetic­field detector on the rover could gain valuable insights into Mars’s past magnetic field, which would have shielded the planet from radiation, says Flannery. And its ground­penetrating radar will help discern some of the geological structures just below the surface of the planet, he says. The mission “promises to be a milestone in XINHUA NEWS AGENCY/SHUTTERSTOCK NEWS XINHUA Chinese and global exploration of the planet”, Tianwen-1 is scheduled to arrive at Mars in February. says Clarke. “It will mean new and complemen­ tary data about Mars from orbit and from a By Smriti Mallapaty at Queensland University of Technology in new location on the Mars surface.” Brisbane, Australia. A lot could still go wrong, Mars has been a major focus of NASA’s Chinese spacecraft is on its way to he says, “but so far so good”. space exploration, says Katarina Miljkovic, Mars after launching successfully Chinese officials have been tight­lipped a planetary scientist at Curtin University in from Hainan Island in southern China.

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