A second run of the model showed that the most powerful comet shower of the last 500 million years might have caused a minor extinction event about 40 million years ago. But collisions could not have been responsible for any major extinction events in that time. "The occurrence of these comet showers is much less frequent than people previously argued," said Hal Levison, a planetary scientist at the Southwest Research Institute in Boulder. The inner Oort cloud, he added, is "not as massive as people who want to use it as an extinction-generator would argue needs to be there." Looking forward, the chance of comet impacts in our lifetime just went from none to even less. "I'm not a big fan of worrying about impacts on the Earth now," Levison said. "Our society has more important things to worry about." Related Links: Comet Dust Collected by NASA Predates Solar System Get More NewsSpiders, Scorpions Among World's Oldest CreaturesMany creepy crawlies have been on Earth much longer than previously believed.Blood-Sucking Vampire Bats Sing DuetsWhite-winged vampire bats "harmonize" with separated roost mates.Oldest Hebrew Writing Possibly FoundAncient inscriptions on a 3,000-year-old pottery shard could make history.Rare, Prehistoric-Age Reptile Found in N.Z.A tuatara has been spotted on the New Zealand mainland for the first time in 200 years.Iceman Has No Living RelativesOetzi, the 5,300 year-old frozen mummy, left no living genetic legacy.SLIDE SHOW: Landscapes of TerrorWhat makes a place feel scary? There are scientific explanations.It's Official: People Are Warming the PolesHumans are conclusively to blame for polar warming, say scientists.Eight-Armed Animal Preceded DinosaursWhat may be one of Earth's first animals was no bigger than a coaster and had eight arms.Phoenicians Live on in People's GenesOne in 17 Mediterranean men may be descended from ancient Phoenicians.Pesticides, Fertilizers Linked to Frog DeclineA pesticide is found to promote parasites among amphibians.Hubble Telescope Taking Photos AgainThe Hubble Space Telescope is once again snapping stunning photos of the universe.Andean Mummy Hairs Show Hallucinogen UseScientists find direct evidence of hallucinogenic drug use among ancient Andeans.Opals on Mars Reveal Planet's Long Wet PastOpals found on Mars suggest the planet has been wet for much longer. |
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