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Scientists discover yet another huge asteroid impact crater

Time:2023-02-03 03:37:17 author:Small size Read:130次
Scientists discover yet another huge asteroid impact crater

The drawing shows a cross-section of an asteroid hitting Earth, similar to the one that wiped out three-quarters of all species on Earth about 66 million years ago. Another impact crater may have been discovered off the coast of West Africa, giving the mass extinction event a new twist. Graphics: CLAUS LUNAU, SCIENCE SOURCE TEXT: MAYA WEI-HAAS After a catastrophic moment about 66 million years ago, the course of life on Earth was changed forever. A meteorite about 9.7 kilometers wide hit the coast of Mexico's Yucatan peninsula, triggering a global catastrophe. The ensuing gigantic tsunami swept thousands of kilometers of coast. Wildfires raged across vast swathes of land. The gases released by the evaporation of rocks on the seafloor cause dramatic climate fluctuations. The catastrophe wiped out about 75 percent of all species on Earth, including all non-avian dinosaurs. But that might not be the full story. Something buried beneath the sand off the coast of West Africa hints that more than one giant meteorite may have hit Earth. According to a new study published in the journal Science Advances, researchers on seafloor seismic surveys have uncovered a deep crater that may be a crater about 8.5 kilometers wide and named after a nearby submarine volcano. Nadir" appears to have been formed by the impact of a meteorite at least 402 meters wide, and it may have been formed around the same time as Chicxulub. Chicxulub Crater is the huge scar left by the asteroid that wiped out the dinosaurs. "Many people have questioned the impact of the Chicxulub collision, but how could it be so devastating on a global scale," said study author Veronica Bray, a planetary scientist at the University of Arizona. Answering that question helps." The material that formed Nadir was much smaller than the Chicxulub meteorite, so its impact could be regional. But the study, if confirmed, suggests that a second meteorite strike in rapid succession may have caused a chain of blows in the end-Cretaceous global catastrophe. In one hypothesis, the pair may have come from the same parent body that split in half before colliding with Earth's atmosphere, hitting the ground more than 5,472 kilometers away. While further analysis is needed to confirm the age and identity of the suspected crater and whether it is related to the Chicxulub meteorite, scientists are excited about the new impact site that may be discovered, but not too excited. Earth's record keeping of ancient impacts is very incomplete due to active geological fluctuations. Large areas of the surface were retracted into the mantle, some areas were recapped by new volcanic rock, and others were eroded away by moving glaciers. Only about 200 impact craters have been identified on Earth, and scientists cannot fully understand how these impacts affected the ancient Earth or what role they might play in Earth's future. "The Earth really wiped out a lot of craters," said Jennifer Anderson, an experimental geologist at Winona State University who studies impact craters but was not part of the team. Because of Earth's active geology, "it's always important to discover new craters on Earth," she said. Earthquake Surprises Like many discoveries, the discovery of suspected new craters was accidental. Uisdean Nicholson, a geologist at Heriot-Watt University in Edenberg, is interested in reconstructing how South America separated from Africa some 100 million years ago. To find clues, Nicholson studied the features of the seafloor between the two continents and obtained seismic data in partnership with commercial companies WesternGico and TGS. The analysis traces how seismic waves bounce off the ground to reveal the structure of the subsurface. The moment he saw the tracking results, Nicholson noticed something strange. As a seismic survey expert, Nicholson has seen a lot of data on the formation of uplift and depression features in subterranean rock formations, such as salt domes arching out of denser surrounding rock. But the data swings before him hint at an even bigger disaster. "I've never seen anything like this," he said. Nicholson contacted other scientists, including Bray, to ask if they thought it might be a crater, and the other scientists agreed: The structure is concave, with a crater rim and a prominent cone in the center. Common in craters. By analyzing the shape and size of the structure, the team simulated how it might have formed. It turned out that the crater was formed by the impact of a roughly 402-meter-wide space rock that roared through the atmosphere and hit the ocean at nearly 72,420 kilometers per hour. When it slammed into the ocean, Bray said, "the ocean couldn't feel it moving at all." The team estimates that the collision would have released the equivalent of 5,000 megatons of TNT explosive, which could almost instantly send the surrounding seawater and ocean floor layers. evaporation. The shock wave then travels through the surface, causing the once-hard rock to flow like a liquid. Within minutes, the seabed would bounce up in the center of the impact location and collapse. The result would be a mountain cone in a bowl-shaped depression -- the very structure the scientists believe they've found off the west coast of Africa. By comparing sediment layers in the area with older samples from other sites, the researchers estimate that the landform was formed about 66 million years ago and is very similar to Chicxulub. Planetary combo? Studying the environmental impact of the Nadir event could help us better understand the possible future impacts on our planet. The Nadir meteorite is theoretically about the size of the asteroid Bennu, which has a 1 in 1750 chance of colliding with Earth over the next three centuries, making it one of the most likely asteroids to hit Earth. An asteroid hitting Earth is by no means trivial, triggering a tsunami that sweeps hundreds of kilometers. Or as Bray puts it: "It's big enough to wipe out a city or two." But what this discovery means for our understanding of what happened after the Chicxulub collision and the extinction of the dinosaurs remains uncertain. The energy released by the Nadir impact and its impact on the environment pales in comparison to the Chicxulub collision with Earth and the ensuing global catastrophe. "It's a whole different class," says Martin Schmieder, an expert on large-scale shock structures at the University of Applied Sciences Neu-Ulm, Germany, who peer-reviewed the study before it was published. But Bray said that in an already devastated ecosystem, the impact of the Nadir impact could make the situation "much worse". There is also the question of whether there were other effects during the same period. The authors of the study noted that the impact that formed the Ukrainian Potes crater occurred 65.4 million years ago, a little later than Chicxulub. Impact swarms from comet or asteroid debris have been recorded before on Earth and other worlds. For example, near where Anderson lives in the American Midwest, there are three craters dating back about 460 million years. They are part of an Ordovician-period impact peak, which scientists believe is related to possible collisions in the asteroid belt, which has been flooded with meteorites toward our planet over millions of years. Identifying these clusters in Earth's sporadic records of ancient impacts, however, is no small challenge. Estimates for impacts the size of Nadir are all slightly less than once every 100,000 years, Schmieder said. "So this can basically happen at any time." And for Nadir, more research is needed to determine how it came about. "This is an exciting discovery," Gareth Collins, a planetary scientist specializing in impact craters at Imperial College London, wrote in an email, although he cautioned that too much can't be drawn on the discovery yet. Direct samples are needed to confirm the origin of the structure and a more precise date of its possible influence in its formation. The study's authors have applied for emergency funding to drill into Nadir's formations to collect samples of the crater's rock and sedimentary layers above it that may have been impacted, melted and mixed. The thick layers of sand and mud that buried the structure may not only preserve the crater's features, but could also help reveal the state of marine life in the years after the impact -- providing an insight into what happened to Earth when the asteroid struck. A new treasure trove of data. "But of course," Bray said, "we won't know for sure until we drill into the formation."

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