SE-Ed: Why Is the Ocean Salty?

If you've ever swallowed a mouthful of seawater,

如果你曾經嗆過一口海水，

you'll know how horribly salty it is!

你就知道它有多鹹了！

Yet the rivers that flow into the ocean taste fresh.

可是，流進大海的河水卻是淡的。

So where does all that salt actually come from?

那麼，這麼多鹽到底是從哪兒來的？

Surprisingly, the story begins with rain!

出人意料的是，故事要從雨說起！

As rain falls through the air,

雨水穿過空氣落下時，

it absorbs a tiny amount of carbon dioxide.

會吸收極少量的二氧化碳。

This makes it very slightly acidic.

這讓雨水帶上了一點點酸性。

Over thousands of years, it slowly wears away the rocks,

經過成千上萬年，它慢慢侵蝕岩石，

releasing tiny bits of minerals, including salt.

釋放出包括鹽在內的微小礦物質。

Rivers then carry these minerals down to the sea.

然後，河流把這些礦物質帶進大海。

So why don't rivers taste salty too?

那麼，河水為什麼不鹹呢？

The amount of salt in a river is tiny,

河水裡的鹽分非常少，

and it's constantly being carried away.

而且一直在被沖走。

The ocean, on the other hand,

而海洋呢，

has been collecting salt for hundreds of millions of years.

已經積攢鹽分好幾億年了。

And here's the clever part!

接下來是最妙的部分！

When the sun heats the ocean, water evaporates,

當太陽把海水曬熱時，水會蒸發，

but the salt is left behind.

但鹽會留下來。

That water later falls as rain, and the cycle starts again.

這些水之後又化作雨落下，循環重新開始。

Rain, rivers, sunshine, repeat — for millions of years!

下雨、河流、日曬，周而復始——持續了幾百萬年！

Rivers aren't the only source, though.

不過，河流並不是唯一的來源。

Deep on the ocean floor, there are cracks called hydrothermal vents.

在深深的海底，有一些叫作熱泉噴口的裂縫。

Seawater seeps into the rock and gets heated by magma,

海水滲進岩石，被岩漿加熱，

then shoots back out, full of dissolved minerals!

然後帶著滿滿的溶解礦物噴湧而出！

Underwater volcanoes add even more.

海底火山還會再添一些。

Around three and a half percent of seawater is salt.

海水中大約百分之三點五是鹽。

Most of it is sodium and chloride, which make up table salt.

其中大部分是鈉和氯化物，也就是構成食鹽的成分。

That might not sound like much.

聽起來好像不算多。

But if you removed all the salt from the oceans

但如果你把海洋裡所有的鹽都取出來，

and spread it evenly over the land,

再均勻地鋪滿陸地，

it would form a layer over one hundred and fifty metres deep!

它會形成一層厚度超過一百五十公尺的鹽層！

That's taller than a forty-storey building!

比一棟四十層的大樓還高！

Some seas are even saltier than the ocean.

有些海比大洋還要鹹。

The Dead Sea is nearly ten times as salty,

死海的鹹度幾乎是海水的十倍，

so swimmers float on top like corks!

所以人在裡面會像軟木塞一樣浮起來！

So will the oceans keep getting saltier forever?

那麼，海洋會一直越來越鹹下去嗎？

Probably not, because salt also leaves the water.

可能不會，因為鹽也會離開海水。

It's slowly buried in the mud and rock of the seabed.

它會慢慢被埋進海底的泥沙和岩石裡。

Scientists believe this balance has stayed steady for a very long time.

科學家認為，這種平衡已經穩定了很長很長時間。

Just remember: drinking seawater only makes you thirstier!

記住一點：喝海水只會讓你更渴！