unit 4 astronomy: the science of stars
导读：据研究,6500万年前的小行星撞击地球，对地球造成了几乎是毁灭性的破坏，有人认为这可能是恐龙灭绝的原因。如果是这样，那么未来再有这样的小行星或彗星撞击地球，会不会导致人类的毁灭呢？
it's said that a huge asteroid(小行星)smashed(撞击) into the earth 65 million years ago, which certainly sent the earth's ecosystem(生态系统) into a disaster which took thousands of years to recover from. scientists say that it's probable that such disaster could happen again.
asteroids are rocky bodi资源难易程度:★★★★★★★★★★★★★★★
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