Where did Earth’s water come from? - Zachary Metz

翻译人员: Min WANG 校对人员: Chen Zou

It has no taste, color or smell, and we often look right through it.

它没有味道，颜色，或者任何气味 而且透明

It covers over 70% of the Earth,

它覆盖了70%的地球表面

cycling from the oceans and rivers to the clouds and back again.

通过海洋，河流到云层 循环往复

它甚至占了我们身体成份的60%

It even makes up about 60% of our bodies.

With all this water around and inside us,

由于我们身边和体内有这么多的水

it's easy to take its presence for granted.

我们觉得水的存在 理所当然

But in the rest of the solar system, liquid water is almost impossible to find.

但是在太阳系的其它地方 几乎找不到液态的水

So how did our planet end up with so much of this substance

那么我们的星球怎么会 有如此多的这种物质

and where did it come from?

它到底来自哪里？

As you probably know,

就像你大概会知道的

一个水分子由 两个基本部分组成

a water molecule consists of two basic parts.

Hydrogen, the simplest of all elements,

氢原子－所有元素中最简单的元素

has been around since close to the beginning of our universe.

自宇宙诞生时就有

氧原子映入眼帘是在 几亿年

Oxygen entered the scene several hundred million years later

星球开始形成之后

after stars began to form.

在这些炽热的如地狱般的中心压力巨大

The massive pressure at the center of these fiery infernos was so great

that hydrogen atoms fused together to form helium.

使得氢原子聚变产生氦原子

Helium, in turn, fused to form heavier elements,

氦原子接着聚变产生其他重原子

like beryllium, carbon and oxygen in a process known as nucleosynthesis.

如铍，碳，以及氧原子， 这样的过程叫做核合成

当星球最终坍塌 爆炸形成超新星

When stars eventually collapsed and exploded into supernovas,

these new elements were spread across the universe

这些元素就 遍及整个宇宙

and combined into new compounds, like the now familiar H2O.

并且合成新物质 就像我们熟知的水分子

These water molecules were present in the dusty cloud

这些水分子 存在于尘云之中

that formed our solar system

尘云形成了我们的太阳系

and more collided with our planet after its formation.

并且在形成之后 与我们的星球发生了更多碰撞

But there's a big question that we don't have the answer to:

但是这里有一个大的疑问 我们还没有对此有答案：

how much water arrived on Earth, and when?

多少水到达了地球，以及何时到达的地球？

如果按一种理论

If, as one theory goes,

relatively small amounts of water were present on Earth when the rock formed,

当岩石形成之时 有相对少的水到达了地球

the high temperatures and lack of any surrounding atmosphere

高温以及缺少大气

would have caused it to evaporate back into space.

会导致水很快 挥发回到了太空

Water would have been unable to remain on the planet

水就不可能保存在地球上

until hundreds of millions of years later

直到亿万年之后

when our first atmosphere formed through a process called outgassing.

当我们的第一个大气层 通过释气过程形成的时候

This occurred when molten rock in the Earth's core

这个过程发生在 岩石在地核融化的时候

released volcanic gasses to the surface,

释放火山气体到地表

creating a layer that could then trap escaping water.

产生了可以捕捉到 逃逸水分子的一层大气

So how then did water get back to the planet?

那么水是怎样 回到地球的呢？

Scientists have long suspected

科学家们长期怀疑

that much of it was brought by ice-bearing comets,

大部分水来自带冰的彗星

or more likely asteroids that bombarded the Earth over millions of years.

或者更可能来自百万年间 撞击地球的小行星

Recent research has challenged this theory.

最近的研究 挑战了这个理论

In examining carbonaceous chondrite meterorites

根据对太阳系诞生后即形成的

that formed shorty after the birth of our solar system,

碳质球粒陨石的化验

scientists have found that not only did they contain water,

科学家们发现 这些陨石不仅含水

but their mineral chemical composition matched rocks on Earth

而且它们的矿物化学成分 与地球岩石

and samples from an asteroid that formed at the same time as our planet.

以及与跟地球同时期形成的 小行星的样品一致

This suggests that the Earth may have accumulated

这个发现表明了 地球可能在早期累积了

a substantial amount of water early on that was able to stay put,

大量的可以保留的水

despite the lack of an atmosphere,

尽管在缺乏大气的情况下

though asteroids may have brought more over the eons.

尽管小行星也许会 日积月累带来更多的水

If this turns out to be true,

如果这是真的

life may have formed much earlier than previously thought.

生命可能在比之前认为的 更久前的时间形成

So we do not yet definitively know whether the water on Earth

所以我们不是绝对地知道 是否地球上的水

came from its initial formation,

来自于它最初的形式

later impacts,

还是受后期的影响

or some combination of the two.

或是两者皆有

Regardless, the water that runs from our showers, drinking fountains and faucets

不管怎样，洗澡用的水 饮用的水，以及自来水

is something that didn't just come from a nearby lake or river,

不是直接来自 附近的河流湖泊

but first underwent a cosmic and chaotic journey to get here.

而是首先经历一个混沌的宇宙漫长 的旅途到达这里