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随身英语 Dangers from outer space 来自外星的危险 Play audio file 地球已经存在了 46 亿年，在此期间它经受了一些灾难性的事件，比如陨石冲击和气候的巨大改变。那么未来又会是怎样呢？系好安全带，让我们一起探讨那些来自外星际对地球可能会造成的危险。 课文内容 Vocabulary: Science 词汇: 科学 What is the greatest threat to life on our planet? Is it climate change? Shortages of food or water? Or might an altogether bigger danger come from somewhere further away: space? We’re not talking about an invasion by little green men here. Instead, how about the prospect of being hit by a gigantic meteorite, zapped by lethal cosmic rays or fried by the deadly energy of an erupting star? It wouldn’t be the first time. Good old planet Earth has had a rough ride over the last 3.7 billion years, with some spectacularly devastating events. The most famous mass extinction was 66 million years ago, when it’s widely believed a meteorite killed off the dinosaurs. A 110-mile-wide crater in Mexico with the same geological age supports this theory. Believe it or not, this wasn’t the most brutal episode in our planet’s history. That was when a staggering 96% of life was wiped out at the end of the Permian period, 252 million years ago. Scientists don’t know for sure why this happened, but any potential explanations carry with them the grim possiblity that similar events could happen again. | 
