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贝壳是如何形成的

How Seashells Are Made

Thanks to CuriosityStream for supporting PBS Digital Studios.
感谢CuriosityStream对PBS数字频道的支持
Seashells and chalk are both made of calcium carbonate.
贝壳和粉笔的主要成分都是碳酸钙
By itself, the mineral is brittle, crumbly, and soft enough to write out a homework assignment.
粉笔柔软易碎 可以直接拿来书写
Seashells, on the other hand, are wonderfully resilient.
而贝壳则极具韧性
They’re tough, they resist breaking,
它们质地坚硬不易破损
and they definitely can’t be used to doodle on the sidewalk.
也不能用来在路边涂鸦
But they’re still primarily CaCO3.
但它们的主要成分依旧是碳酸钙
So what makes seashells so different?
那么是什么让贝壳与众不同呢?
How can this…and this be made of the same stuff?
为何粉笔和贝壳会是同一种物质构成呢?
We’re talking about the mineral chalk, by the way —
提醒一下 这里我们说的是矿物粉笔
sidewalk and classroom chalk are usually made from a different mineral known as gypsum, but we digress.
插句题外话 和教室专用粉笔不同 街头粉笔通常由石膏制成
Both seashells and mineral chalk are the product of living things.
贝壳和矿物粉笔都是生物制品
Those chalk deposits were generally formed from the gradual buildup
这些物质是由海洋中单细胞生物的
and compression of single-celled ocean organisms with calcified shells.
钙化壳逐渐压缩堆积而成
But bivalve mollusks like oysters and mussels are much more sophisticated shell-builders.
而双壳类软体动物如牡蛎和贻贝都是盖壳高手
When we use that mineral chalk, it’s long dead,
当我们采集矿物时 它们早已死掉
and all that’s left is the crumbly stuff.
而剩下的只有易碎的壳
But these mollusks are pulling dissolved carbonate, and calcium from the ocean
但是这些软体动物正把海中溶解的碳酸盐和碳酸钙
for some pretty fancy biological architecture.
带给一些出色的生物建筑师
Seashells contain 95% or more calcium carbonate.
贝壳中的碳酸盐含量达95%甚至更高
The rest is mostly protein and a bit of sugar.
剩下的大部分是蛋白质 还有一点糖分
But a little biochemistry goes a long way.
但一个小生物化学反应则要很长时间
Calcium carbonate can take on a variety of forms.
碳酸钙的存在形式有很多
Even though its chemical formula never changes,
就算它的化学式永远不变
its crystal structure
它的晶体结构
— which is the 3D arrangement of its atoms in space — does change
即立体原子空间结构也不止一种
The two forms we care about right now are calcite and aragonite.
我们目前研究的两种是方解石和文石
Calcite tends to be more stable than aragonite,
方解石比文石更稳定
but many bivalve shells contain a layer of each
但很多双壳动物贝壳里 两者各有一层
calcite on the outside of the shell, aragonite on the inside.
外面一层是方解石 里面一层是文石
One benefit to layering is that the crystal structures are oriented differently in space.
分层的一个好处是晶体结构在空间上取向不同
If the calcite layer fractures, that fracture will probably stop when it hits the aragonite layer,
如果方解石层裂开 裂缝很可能在抵达文石层时停止
because aragonite doesn’t break the same way.
因为文石裂开的方式不一样
But that alone isn’t nearly enough to make seashells so much tougher than chalk.
但仅仅这样并不足以使贝壳比粉笔更坚硬
We told you mollusks were amazing builders.
我们说过 软体动物是绝佳的建筑师
The aragonite layer in a shell like an oyster’s is called nacre, or mother-of-pearl.
牡蛎中的文石层被称为珍珠层 或者珍珠母
Here’s how scientists have speculated mollusks actually make the stuff.
现在我们来看一下科学家眼中的牡蛎是如何做到这样的
Nacre is made up of layers of aragonite crystals
珍珠层由若干文石晶体层组成
separated by very thin layers of protein
而文石层又被很薄的蛋白质层隔开
Those layers are anchored by a chain of sugars called chitin.
一种叫几丁质的糖链将其固定
Mono- and disaccharides,
这种二糖
the kind of sugars we eat, are water-soluble and not good building materials by themselves.
属于食用糖 可水解而且不可单独使用
Try to build a castle like sugar cubes, see how long it lasts.
试着建一座糖方 看它能维持多久
But chain them together in long strings called polysaccharides,
但如果把它们连成叫做多糖的长链
and they can become tough and fibrous.
那就成了坚固的纤维
Chitin is one such polysaccharide.
几丁质就是这样的多糖
Proteins attached to the chitin layer
蛋白质附着在几丁质层上
give the calcium carbonate crystals a place to start growing.
为碳酸钙晶体提供生长场所
Those proteins have charged regions that attract the minerals.
吸引矿物质的区域由这些蛋白质掌控着
Because of how those regions are spaced,
基于这些区域的空间构造
the crystals can grow in regular chunks
晶体以块状规律生长
until they hit the next layer and meet each other at the edges.
最后延伸至边缘 包裹下一层并融合在一起
That’s not everything the proteins and polysaccharides do.
蛋白质和多糖的任务远不止这些
Shell formation requires a whole army of complex biological molecules,
贝壳的形成需要各种各样复杂的生物分子的参与
and scientists are still trying to understand how it all goes down.
科学家们仍在研究这个过程是如何进行的
Nacre is literally thousands of times tougher than chalk, thanks to the layers of protein
多亏了蛋白质和几丁质层 以及精确的结构控制
and chitin, and the precise structural control.
珍珠层才比粉笔更坚硬
And the oysters go on to make pearls.
牡蛎才能继续合成珍珠
They’re so talented!
它们太厉害了
What all that means is that mollusks don’t just wear these minerals as a hat.
这意味着贝壳软体动物并不只是将它当做帽子
They control how the shell is made,
它们指挥贝壳的建造
and what kind of crystal forms — whether calcite or aragonite
和晶体的使用–是方解石或者文石
They can make all sorts of neat shell shapes that don’t look anything like a stick of chalk.
它们可以造各种与粉笔差别很大的贝壳
And they can even remodel their shells throughout their lifetime.
甚至一生都可以重复建造
And that’s why you can’t make sidewalk doodles with a seashell.
这就解释了为什么你没法用贝壳在街头涂鸦
Which works out great for the animal, after all.
因此也保护了贝类软体动物
Thank you to CuriosityStream for supporting PBS Digital Studios.
感谢CuriosityStream对PBS数字频道的支持
CuriosityStream is a subscription streaming service
CuriosityStream提供流媒体服务
that offers documentaries and non-fictiontitles from a variety of filmmakers,
有纪录片和来自许多电影制作人的非虚构资源
including CuriosityStream originals.
其中也有CuriosityStream原创内容
For instance,CuriosityStream offers Space Probes,
比如 里面有航天类节目
where you can learn all about the intrepid robots we’ve sent to distant worlds.
你可以了解所有关于我们送到外太空的机器人的事
You can learn more at curiositystream.com slash reactions
你可以在网站里学到更多
and use the code reactions during the sign-up process.
在订阅时请使用代码
Hey, if you liked this video, don’t be…shellfish.
嘿 如果喜欢我们的视频 那就分享起来
Share it with everyone you know, and be sure to subscribe and hit notifications
把它分享给你认识的人 记得订阅并点击通知
because it really really helps us out and enables us to make more awesome videos like this one.
因为在制作本视频的时候 它真的帮了我们不少
Thanks for joining us, and we’ll see you next time.
感谢收看 我们下期见

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视频概述

你知道贝壳的结构吗?如此弱小的生物也能造出坚固的房子,生命真的很伟大

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视频来源

https://www.youtube.com/watch?v=iUeMxjkSPyM

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