How do oysters make pearls? - Rob Ulrich

譯者: Lilian Chiu 審譯者: Helen Chang

While most people wouldn’t consider the crusty exterior of an oyster

雖然大部分人不認為 牡蠣的堅硬外殼

to be particularly beautiful,

有什麼特別漂亮之處，

opening up this craggy case might reveal an exquisite jewel nestled within.

但打開這粗糙不平的外殼可能會露出

安臥在內的精美珍寶。

Yet, despite their iridescent colors and smooth shapes,

然而儘管珍珠的 顏色燦爛且形狀光滑，

pearls are actually made of the exact same material

其實珍珠的組成材料

as the shell that surrounds them.

和它們的外殼相同。

Pearls, urchin spines, the shells of mussels, snails and clams, even coral—

珍珠、海膽的刺、蚌類的殼、 蝸牛和蛤蜊，甚至珊瑚——

all these structures are made out of the same chemical compound:

所有這些構造都是 由同樣的化合物組成：

calcium carbonate.

碳酸鈣。

So, how does this single ingredient form such a vast array of materials?

這單一種成分，如何能

形成這麼多樣化的材料？

Calcium carbonate, or CaCO3, is common on land,

碳酸鈣，即 CaCO3，

在陸地上很常見，在海中更是豐富。

and even more bountiful in the sea.

The Earth’s crust is rich in calcium,

地球的地殼富含鈣，經過數百年，

and over millennia these deposits have seeped into rivers and oceans.

這些沉澱物漸漸滲流到河中和海中。

This is especially true near hydrothermal vents,

這個現象在深海溫泉區更是明顯，

where hot seawater mingles with calcium rich basalts.

在那裡，熱海水 混合富含鈣的玄武岩。

Meanwhile, when carbon dioxide in the air interacts with seawater

同時，當空氣中的二氧化碳 和海水產生交互作用，

it eventually produces dissolved carbonate.

最終會產生出溶解的碳酸鹽。

Every year, the ocean absorbs roughly one third of our carbon dioxide emissions,

每年，海洋會吸收

大約三分之一我們 排放出來的二氧化碳，

adding huge quantities of carbonate into the water.

讓水中增加大量的碳酸鹽。

It’s no surprise that sea creatures have made use of these abundant compounds,

海洋生物會善用如此充足的 化合物，並不讓人意外。

but the way calcium and carbonate are woven together into various shapes

但鈣和碳酸鹽交織在一起 成為各種形狀的方式

is surprisingly artful.

卻巧妙到讓人吃驚。

Let’s return to the humble oyster.

咱們再回到卑微的牡蠣。

Like many aquatic mollusks, oysters start life as exposed larvae,

和很多水中的軟體動物一樣，

牡蠣剛誕生時，是暴露在外的幼體，

and quickly get to work building a protective shell.

牠很快就開始動工 建造保護用的外殼。

First, an organ called the mantle secretes an organic matrix

首先，叫做「套膜」的器官

會分泌蛋白質及其他分子的 有機基體，以建造骨架。

of proteins and other molecules to construct a scaffold.

Then, the oyster filters the seawater,

接著，牡蠣會過濾海水，

drawing out calcium and carbonate to combine them into its building material.

取出鈣及碳酸鹽，將兩者結合，

組成建材。

It lays this material over the scaffold,

它把這建材舖在骨架上，

which is covered in charged proteins that attract and guide

它上面覆蓋著帶電的蛋白質，

能夠吸引和引導碳酸鈣分子 變成一層一層的形式。

the calcium carbonate molecules into layers.

The specific arrangement of these protein scaffolds depends on the mollusk species

這些蛋白質骨架會如何排列，

就要看軟體動物的物種 和牠們的環境，

and their environment,

accounting for their vast diversity of shell shapes, sizes, and colors.

這就說明了為何牠們會有 各式各樣的外殼形狀、

大小，及顏色。

Mollusks carefully control all components of their calcium carbonate creations—

軟體動物會很小心地控制其 碳酸鈣作品的所有成分——

even manipulating CaCO3 at the molecular level.

甚至在分子層級操控 CaCO3。

Using special proteins,

靠著特殊的蛋白質，

mollusks can produce two crystal structures out of CaCO3:

軟體動物能用 CaCO3 產生出兩種晶體結構。

calcite and aragonite.

方解石和霰石。

Both of these compounds have the same chemical composition,

這兩種化合物有同樣的化學組成，

but different qualities due to the way their crystal lattices are arranged.

但特性不同，

因為它們的晶格排列方式不同。

Calcite is the more stable of the two and less prone to dissolving over time,

這兩者中，方解石比較穩定，

且比較不會隨時間溶解，

so most mollusk shells have a sturdy outer layer of calcite.

所以大部分軟體動物的外殼 都有一層堅固的方解石。

As the slightly more soluble molecule,

身為稍為較容易溶解的分子，

aragonite can better adapt to more or less acidic environments.

霰石對於比較酸／不酸的環境 都能適應較良好。

So most mollusk shells have an interior layer of aragonite

所以大部分軟體動物的外殼， 裡面都有霰石內層，

to maintain their internal pH level.

維持牠們內部的酸鹼值。

But one form of aragonite is stronger and more versatile than the rest:

但有一種霰石的形式， 比其他種類更堅固、更多功能：

nacre.

珍珠母。

Mollusks make this special material by placing successive layers of aragonite

軟體動物製造這種特殊材料的 方式，是把連續數層的霰石

interspersed with proteins.

和蛋白質一起散布排放。

These layers are stacked like hexagonal bricks,

一層一層如同六角形磗般堆疊起來，

each surrounded by other organic material that directs their orientation.

每一層都被其他的有機材料 包覆，用來引導其方向。

The uniform layering and brick-like structure of nacre

珍珠母的一致層疊方式 以及類似磚塊的結構，

is key to its signature iridescence.

是造成它招牌燦爛色彩的關鍵。

The layers are similar in thickness to the wavelength of visible light,

各層的厚度和可見光的波長類似，

so the light reflecting from its interior surface

因此內部表面所反射的光

interferes with the light reflecting from the outer surface.

會干擾外部表面所反射的光。

When particles of light strike the nacre,

當光的粒子撞擊到珍珠母，

they bounce around its multilayered crystalline structure

便會在其多層結晶結構中彈來彈去，

in a cascade of shifting rainbows.

產生出一連串不斷變換的彩虹。

But nacre isn’t just pretty—

但珍珠母不僅是漂亮——

it’s one of the strongest and lightest biomaterials we know of.

它是我們所知最堅固 且最亮的生物材料之一。

And it's not just oysters that produce it.

且不只有牡蠣會製造它。

In fact, numerous mollusk species deploy nacre

事實上，許多軟體動物物種 都會部署出珍珠母，

as one of their primary defense mechanisms.

做為牠們主要的防禦機制之一。

If an intruding parasite or even a stray particle of sand irritates the mantle,

如果有入侵的寄生蟲 或甚至迷路的沙子

刺激到了套膜，

the mollusk will coat the offender in nacre-producing cells

軟體動物會用產生珍珠母的 細胞把入侵者覆蓋住，

to form what’s known as a pearl sac.

形成一般所知的珍珠囊。

These cells wrap the threat in layers of proteins and aragonite

這些細胞用數層蛋白質 和霰石把威脅包裏起來，

until eventually the cocoon completely absorbs the invader—

直到最後繭狀物 完全吸收掉入侵者——

dissolving the threat into an opalescent sphere of nacre.

把威脅溶解成乳白色的珍珠母球體。

This defense mechanism is our leading theory for mollusks making pearls;

關於軟體動物為什麼要製造珍珠，

我們主要的理論就是這種防禦機制；

transforming everyday intruders into timeless treasures.

將日常的入侵者轉換

成為永恆的珍寶。