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 conclusive¹ 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 asteroids² 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 collapsed³ to form our sun and the planets around it.”

　　Some scientists have theorized it may have been a comet strike that killed the dinosaurs⁴ 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 astronomical⁵ 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 outermost⁶ 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.

1 conclusive   

adj.最后的，结论的；确凿的，消除怀疑的

参考例句：

• They produced some fairly conclusive evidence.他们提供了一些相当确凿的证据。
• Franklin did not believe that the French tests were conclusive.富兰克林不相信这个法国人的实验是结论性的。

2 asteroids   

n.小行星( asteroid的名词复数 )；海盘车，海星

参考例句：

• Asteroids,also known as "minor planets",are numerous in the outer space. 小行星，亦称为“小型行星”，在外太空中不计其数。
• Most stars probably have their quota of planets, meteorids, comets, and asteroids. 多数恒星也许还拥有若干行星、流星、彗星和小行星。

3 collapsed   

adj.倒塌的

参考例句：

• Jack collapsed in agony on the floor. 杰克十分痛苦地瘫倒在地板上。
• The roof collapsed under the weight of snow. 房顶在雪的重压下突然坍塌下来。

4 dinosaurs   

n.恐龙( dinosaur的名词复数 )；守旧落伍的人，过时落后的东西

参考例句：

• The brontosaurus was one of the largest of all dinosaurs. 雷龙是所有恐龙中最大的一种。 来自《简明英汉词典》
• Dinosaurs have been extinct for millions of years. 恐龙绝种已有几百万年了。 来自《简明英汉词典》

5 astronomical   

adj.天文学的，（数字）极大的

参考例句：

• He was an expert on ancient Chinese astronomical literature.他是研究中国古代天文学文献的专家。
• Houses in the village are selling for astronomical prices.乡村的房价正在飙升。

6 outermost   

adj.最外面的，远离中心的

参考例句：

• He fired and hit the outermost ring of the target.他开枪射中了靶子的最外一环。
• The outermost electron is shielded from the nucleus.原子核对最外层电子的作用受到屏蔽。