Name: How do oysters make pearls? - Rob Ulrich
Uploaded: 2022-11-20T04:54:00.000Z
Duration: 5 min 23 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

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

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

Yet, despite their iridescent colors and smooth shapes,

pearls are actually made  of the exact same material

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

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

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

Calcium carbonate, or CaCO3,  is common on land,

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

This is especially true  near hydrothermal vents,

where hot seawater mingles  with calcium rich basalts.

Meanwhile, when carbon dioxide in the air interacts with seawater

it eventually produces dissolved carbonate.

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

adding huge quantities of carbonate into the water.

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

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

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

and quickly get to work building a protective shell.

First, an organ called the mantle secretes an organic matrix

of proteins and other molecules  to construct a scaffold.

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

which is covered in charged proteins that attract and guide

the calcium carbonate molecules into layers.

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

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

Mollusks carefully control all components  of their calcium carbonate creations—

even manipulating CaCO3  at the molecular level.

mollusks can produce  two crystal structures out of CaCO3:

Both of these compounds have  the same chemical composition,

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

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

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

aragonite can better adapt  to more or less acidic environments.

So most mollusk shells have  an interior layer of aragonite

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

Mollusks make this special material by placing successive layers of aragonite

These layers are stacked like hexagonal bricks,

each surrounded by other organic material that directs their orientation.

The uniform layering and brick-like structure of nacre

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

so the light reflecting  from its interior surface

interferes with the light reflecting  from the outer surface.

When particles of light strike the nacre,

they bounce around its multilayered  crystalline structure

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

And it's not just oysters that produce it.

In fact, numerous mollusk species deploy nacre

as one of their primary defense mechanisms.

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

the mollusk will coat the offender  in nacre-producing cells

These cells wrap the threat in layers  of proteins and aragonite

until eventually the cocoon  completely absorbs the invader—

dissolving the threat into an opalescent  sphere of nacre.

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

transforming everyday intruders into timeless treasures.

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How do oysters make pearls? - Rob Ulrich

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