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A quarter of a million miles up is the earth's last hope of defense.
在25万英里高空，是保卫地球的最后希望。
The Moon has saved the planet before.
月球曾经拯救过地球。
Its pockmarked surface bears the scars of countless collisions.
它千疮百孔的表面上留有无数次碰撞留下的伤痕。
This crater, known as Tycho, is more than 50 miles wide, created by a rock only half the size of the one that's on its way.
这个被称为第谷(Tycho)的陨石坑宽50多英里，由一块只有正在撞击的陨石坑一半大小的岩石形成。
But the Moon is rarely in the right place at the right time.
但是月球很少在正确的时间出现在正确的地点。
Nothing can stop the asteroid now.
现在没有什么能阻止这颗小行星了。
This cosmic missile isn't as alien as it seems.
这颗宇宙飞弹看起来并不陌生。
Like the earth itself. It's made up largely of rock and water.
就像地球本身这个小行星绝大部分由岩石和水组成。
In the cold vacuum of space, the water freezes into a hard permafrost.
在寒真空的太空里水凝固成坚硬的永冻层。
But on the inside, there's a chemical cocktail composed of carbon, hydrogen and oxygen.
不过在里面有一种化学混合物，当中包括碳氢和氧
Key ingredients for lifes.
都是构成生命基本要素。
Asteroid fragments like this one may have provide the building blocks for life on Earth.
像这样的小行星碎块，可能为地球上的生命提供了基本元素
Life, it evolved into dinosaurs.
最后演化成恐龙。
But what gives life, can also take it away.
不过孕育生命的东西也可能夺命
Most dinosaurs in the valley hunt and forage during the day and sleep at night.
山谷里多数恐龙白天猎捕和觅食晚上睡觉
This giant herbivore,an Ankylosaurus keeps one eye open for predators.
这种巨型的草食动物背甲龙对掠食者保持警觉。
Under the cover of darkness, very different creatures emerge from their hiding places.
在黑幕笼罩下截然不同的生物从藏匿处现身
Like Mesodma, a primitive mammal about the size of a possums.
像拟间异兽一种和负鼠差不多大的原始哺乳类。
like most other mammals, Mesodma's life is all about being with the dinosaurs earth.
跟其它大多数哺乳类一样,拟间异兽的首要大事就是避开恐龙
It only comes out at night,to forage for tasty roots and insects.
它只在晚上出来觅食找好吃的根和虫子
While the giants sleep, It's the meek that witness a cosmic event.
巨龙沉睡时温驯的小动物见证了宇宙异象。
A meteor shower.
一场流星雨。
