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。
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 prospect1 of being hit by a gigantic meteorite2, zapped by lethal3 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 devastating4 events. The most famous mass extinction5 was 66 million years ago, when it's widely believed a meteorite killed off the dinosaurs6. A 110-mile-wide crater7 in Mexico with the same geological age supports this theory.
Believe it or not, this wasn't the most brutal8 episode in our planet's history. That was when a staggering 96% of life was wiped out at the end
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