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The Chicxulub impactor ( ), also known as the K/Pg impactor and (more speculatively) as the Chicxulub asteroid, was an asteroid or comet at least ten kilometres (six miles) in diameter which impacted a few miles from the present-day town of Chicxulub in Mexico, after which the impactor and its crater are named. Because the estimated date of the object's impact and the Cretaceous–Paleogene boundary (K–Pg boundary) coincide, there is a scientific consensus that its impact was the Cretaceous–Paleogene extinction event which caused the demise of the planet's non-avian dinosaurs and other species. The impactor's crater is more than 180 km (110 miles) in diameter, making it one of the largest known impact craters on Earth. Geological evidence shows that the impact dates from the end of the Cretaceous, approximately 66 million years ago. The impact is implicated in causing the mass extinction event at that time, as suggested by the K-Pg boundary, the geological boundary between the Cretaceous and Paleogene periods. Some scientists doubt whether the impact was the sole cause, and others debate whether the Chicxulub impactor was one of several that may have struck the Earth at around the same time.〔(【引用サイトリンク】website=BBC News )〕 In March 2010, following extensive analysis of the available evidence covering some twenty years' worth of data spanning the fields of palaeontology, geochemistry, climate modelling, geophysics and sedimentology, forty-one international experts from thirty-three institutions reviewed the available evidence and concluded that the impact at Chicxulub triggered the mass extinctions at the K–Pg boundary, including those of the dinosaurs.〔〔 ==Astronomical origin== In September 2007, an article by William F. Bottke, David Vokrouhlický, and David Nesvorný published in ''Nature'' proposed an origin for the impactor. This argued that a collision in the asteroid belt 160 million years ago resulted in the Baptistina family of asteroids, the largest surviving member of which is 298 Baptistina. They proposed that the Chicxulub impactor was an asteroid member of this group, referring to the large amount of carbonaceous material present in microscopic fragments of the object, suggesting that it was a member of a rare class of asteroids called carbonaceous chondrites, like Baptistina. According to Bottke, the Chicxulub impactor was a fragment of a much larger parent body about across, with the other impacting body being around 60 km (40 mi) in diameter. However, in 2011 new data from the Wide-field Infrared Survey Explorer revised the date of the collision which created the Baptistina family to about 80 million years ago, casting doubt on the theory, as typically the process of resonance and collision of an asteroid takes many tens of millions of years.〔Tammy Plotner, ''(Did Asteroid Baptistina Kill the Dinosaurs? Think other WISE... )'' in ''Universe Today'' (2011) at universetoday.com〕 In 2010, another theory implicated the newly discovered asteroid P/2010 A2, a member of the Flora family of asteroids, as a possible remnant cohort of the Chicxulub impactor.〔("Smashed asteroids may be related to dinosaur killer" ) Reuters, February 2, 2010〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Chicxulub impactor」の詳細全文を読む スポンサード リンク
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