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The origins of water on Earth have been debated by scientists for hundreds of years.
关于地球上的水的起源科学家们争论了几百年，
Some believe that water was delivered by comets, but recently, there has been mounting evidence for a different explanation.
有些人认为地球上的水源于彗星。然而，最近有越来越多的证据对此提供了不同的解释。
To explore this theory, we have to wind the geologic clock back 4 billion years to a time when the Earth was hot and still forming.
为了探索这一理论，我们必须将地质钟拨回到40亿年前，那时地球还很热，仍在形成当中。
The idea is that water has always been on Earth. Trapped beneath the crust, it's locked in liquid magma.
这一理论是，水一直存在于地球上，被困在地壳之下，锁在液态岩浆之中。
But as the Earth's surface began to cool and harden,
而随着地球表面开始冷却和硬化，
volcanoes acted like a tear in the fabric of our planet, allowing the water to slowly escape.
火山就像地球上的一个裂口，水慢慢从里面逸出，
This water vapor then condensed in our atmosphere and fell as rain.
水蒸气在大气中凝结成雨。
It rained for so long that eventually, our dry, barren Earth turned into a Blue Planet.
雨下了很长时间，终于，我们干燥贫瘠的地球变成了一个蓝色的星球。
Water that we see on Earth mostly comes from volcanoes.
我们在地球上看到的水大多来自火山，
Without volcanoes, there wouldn't be life on Earth, literally.
说白了，没有火山，地球上就不会有生命。
