SE-Ed: Why Is the Ocean Salty?

If you've ever swallowed a mouthful of seawater,

如果你曾经呛过一口海水，

you'll know how horribly salty it is!

你就知道它有多咸了！

Yet the rivers that flow into the ocean taste fresh.

可是，流进大海的河水却是淡的。

So where does all that salt actually come from?

那么，这么多盐到底是从哪儿来的？

Surprisingly, the story begins with rain!

出人意料的是，故事要从雨说起！

As rain falls through the air,

雨水穿过空气落下时，

it absorbs a tiny amount of carbon dioxide.

会吸收极少量的二氧化碳。

This makes it very slightly acidic.

这让雨水带上了一点点酸性。

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

经过成千上万年，它慢慢侵蚀岩石，

releasing tiny bits of minerals, including salt.

释放出包括盐在内的微小矿物质。

Rivers then carry these minerals down to the sea.

然后，河流把这些矿物质带进大海。

So why don't rivers taste salty too?

那么，河水为什么不咸呢？

The amount of salt in a river is tiny,

河水里的盐分非常少，

and it's constantly being carried away.

而且一直在被冲走。

The ocean, on the other hand,

而海洋呢，

has been collecting salt for hundreds of millions of years.

已经积攒盐分好几亿年了。

And here's the clever part!

接下来是最妙的部分！

When the sun heats the ocean, water evaporates,

当太阳把海水晒热时，水会蒸发，

but the salt is left behind.

但盐会留下来。

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

这些水之后又化作雨落下，循环重新开始。

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

下雨、河流、日晒，周而复始——持续了几百万年！

Rivers aren't the only source, though.

不过，河流并不是唯一的来源。

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

在深深的海底，有一些叫作热液喷口的裂缝。

Seawater seeps into the rock and gets heated by magma,

海水渗进岩石，被岩浆加热，

then shoots back out, full of dissolved minerals!

然后带着满满的溶解矿物喷涌而出！

Underwater volcanoes add even more.

海底火山还会再添一些。

Around three and a half percent of seawater is salt.

海水中大约百分之三点五是盐。

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

其中大部分是钠和氯化物，也就是构成食盐的成分。

That might not sound like much.

听起来好像不算多。

But if you removed all the salt from the oceans

但如果你把海洋里所有的盐都取出来，

and spread it evenly over the land,

再均匀地铺满陆地，

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

它会形成一层厚度超过一百五十米的盐层！

That's taller than a forty-storey building!

比一栋四十层的大楼还高！

Some seas are even saltier than the ocean.

有些海比大洋还要咸。

The Dead Sea is nearly ten times as salty,

死海的咸度几乎是海水的十倍，

so swimmers float on top like corks!

所以人在里面会像软木塞一样浮起来！

So will the oceans keep getting saltier forever?

那么，海洋会一直越来越咸下去吗？

Probably not, because salt also leaves the water.

可能不会，因为盐也会离开海水。

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

它会慢慢被埋进海底的泥沙和岩石里。

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

科学家认为，这种平衡已经稳定了很长很长时间。

Just remember: drinking seawater only makes you thirstier!

记住一点：喝海水只会让你更渴！