It covers over 70% of the Earth,

它覆蓋了 70% 以上的地球

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

從海洋、河流進入到雲氣裡 又降回到地面一再重複此循環

It even makes up about 60% of our bodies.

甚至我們人體的 60% 也是水分

With all this water around and inside us,

在我們的週遭和體內有著這麼多水分

it's easy to take its presence for granted.

就很容易把它的存在不當成是一回事

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

但是在太陽系的其他地方 幾乎找不到液態水

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

我們的星球為什麼 會有著這麼多液態水

and where did it come from?

它又到底是從哪裡來到地球的呢

As you probably know,

就像你或許知道的一樣

a water molecule consists of two basic parts.

水的分子是由兩個基本成分組成

Hydrogen, the simplest of all elements,

氫氣 ─ 這最普通的元素

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

大概從我們的宇宙誕生之初 至今就一直存在著

Oxygen entered the scene several hundred million years later

氧氣在星球開始形成 的數億年後也進場來了

after stars began to form.

在這些赤紅火海中心 的巨大壓力是如此之龐大

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

氫原子熔合在一起構成了氦

that hydrogen atoms fused together to form helium.

氦接下來又熔合成了重元素

Helium, in turn, fused to form heavier elements,

在稱為「核合成」的過程裡 熔合成像是鈹、碳、或是氧氣

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

當星球終究瓦解和爆炸成了超新星

When stars eventually collapsed and exploded into supernovas,

這些新元素就散佈到整個宇宙當中

these new elements were spread across the universe

接著結合成新的聚合物， 像是我們今天所熟悉的水 (H2O)

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

這些水分子存在於混濁的雲體當中

These water molecules were present in the dusty cloud

那些雲體又形成了我們的太陽系

that formed our solar system

在太陽系形成後 更多水分撞擊到了地球

and more collided with our planet after its formation.

這邊有個目前找不到答案的大疑問

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

有多少水分來到了地球？ 以及什麼時候來的？

how much water arrived on Earth, and when?

假使像某個理論所說的一樣

If, as one theory goes,

當地球岩體形成時只有 相對少量的水在地球上

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

高溫以及缺少氣體籠罩住地球

the high temperatures and lack of any surrounding atmosphere

會造成水分蒸發而回到太空裡

would have caused it to evaporate back into space.

水分沒有辦法留在這星球上

Water would have been unable to remain on the planet

直到幾億年之後

until hundreds of millions of years later

當我們最早的大氣層經由 「氣體釋出」的過程所形成

when our first atmosphere formed through a process called outgassing.

這發生在當地心裡的熔化岩石

This occurred when molten rock in the Earth's core

釋放出火山氣體到地表

released volcanic gasses to the surface,

創造出一層外覆 然後就可以鎖住外逸的水分

creating a layer that could then trap escaping water.

那麼水分後來是如何回到星球上呢？

So how then did water get back to the planet?

科學人員長久以來猜測

Scientists have long suspected

許多的水分是被冰晶彗星帶來的

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

或更可能是在數百萬年前 小行星群轟炸地球時所帶來的

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

最新的研究對這個理論提出了質疑

Recent research has challenged this theory.

在檢測隕石化石的時候

In examining carbonaceous chondrite meterorites

該隕石是在太陽系誕生不久後形成的

that formed shorty after the birth of our solar system,

科學人員發現到它們不只含帶水分

scientists have found that not only did they contain water,

而且礦物化學成分與地球的岩石、

but their mineral chemical composition matched rocks on Earth

以及與地球同時間形成的 小行星之樣本吻合

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

這代表地球可能早在水分能留住前 就積存了大量的水分

This suggests that the Earth may have accumulated

儘管是缺少了大氣層

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

儘管小行星可能在遠古也帶來了很多水

despite the lack of an atmosphere,

假若這個成為了事實

though asteroids may have brought more over the eons.

生命體可能出現於 比我們以前所知道的還要更早

If this turns out to be true,

所以我們尚未確切地知道 到底地球的水分

life may have formed much earlier than previously thought.

是來自於它最初形成的時候

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

或是之後的影響所造成

came from its initial formation,

抑或夾雜著這兩者的理由

later impacts,

不管如何，從我們的蓮蓬頭、 自來水管和水龍頭跑出來的水

or some combination of the two.

就不單純是從附近的湖泊 或河流所來的東西

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

而是先歷經了一段跟宇宙有關的 不平靜旅程來到了地球

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

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