南非科学家发现首个彗星曾撞击地球证据

 　　南非科学家发现首个彗星曾撞击地球证据

　　JOHANNESBURG — South African researchers say they have found conclusive 1 evidence of earth's first-ever known comet strike, about 28 million years ago. The researchers say this exciting find in rural Egypt could unlock more secrets of the universe.
　　South African academics say the evidence they've found indicates the comet hit the earth some 28 million years ago - in a desert in western Egypt.
　　The bits of glassy black rock left at the scene - which scientists say are comet fragments - could help unlock the secrets of our universe. The academics presented their findings at the University of the Witwatersrand in Johannesburg this month.
　　Meteors and asteroids 2 collide with this planet fairly frequently. But a comet strike, said Professor David Block of the University of the Witwatersrand, is unique and exciting.
　　“Because a comet is this dirty snowball of not only rock, but rock mixed with ice. And the point is that atoms, life-giving atoms of carbon, of oxygen, of nitrogen, of argon, of neon, of krypton, are encoded within this little chemical factory from beyond the solar system," said Block. "These are grains of cosmic dust, which existed prior to our solar system forming. So they contain unique secrets of the chemical compo [composition] of the cloud of gas and dust, which collapsed 3 to form our sun and the planets around it.”
　　Some scientists have theorized it may have been a comet strike that killed the dinosaurs 4 65 million years ago - but there is no evidence.
　　And, said Dr. Marco Andreoli, no one has seen a comet hit and lived to tell about it because they tend to fry every living thing in their path to ashes. He said, though, the evidence of this comet strike is clear to him.
　　“We are looking at something of… an astronomical 5 phenomenon,” he said.
　　Geoscientist Jan Kramers from the University of Johannesburg said that although the scientific community is divided on his team’s conclusions that the fragment is a comet, he himself is fairly certain.
　　“… it’s a probably a comet, because it can’t be anything else, coming from the outermost 6 reaches in the solar system, traveling in the gravity of the sun and hitting the Earth by chance. What it did tells you something more," said Kramers. "What it did when it hit the atmosphere, it exploded. And that is what comets do when they hit the atmosphere. And this explosion produces an incredible amount of heat, which can account for the Libyan desert glass which we found in that region.”
　　The researchers say they hope further study of this comet fragments will help them figure out the beginnings of our universe.