WEBVTT

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Sand, whether you use it
for building sand castles,

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telling time with an hourglass,
or hydraulic fracturing,

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is pretty much the same
just about anywhere

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you go, an uncountable number
of tiny grains mixed together

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to form the same
dunes and beaches.

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But why does sand almost
always look the same?

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And how does so much of
it end up at the beach?

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Well, much of the
world's sand is made out

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of the same stuff, tiny crystals
of the mineral quartz, which

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is made out of silica
and oxygen, the two most

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common elements
in Earth's crust.

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And as you'll know
if you've ever

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been through the crust of a
sandwich that had sand in it,

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quartz grains are
small and really tough.

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Here's why.

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Quartz crystals form
within a cooling glob

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of molten granite
rock, or magma,

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deep under the Earth's surface.

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As the magma cools,
different minerals

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crystallize into solid rock
at different temperatures

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and quartz is one of the
last minerals to form.

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It's forced to crystallize in
the tiny spaces left in the now

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cooling rock, pretty much
ensuring that it ends up

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in a specific size range.

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But being last has
lasting advantages.

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Minerals that do form in the
earlier, hotter conditions

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have weaker chemical structures
and weather away more easily

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than quartz.

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Kind of like how a relationship
forged in the heat of passion

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might not be as stable as a
deep bond developed over time.

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So as the weak flash in
the pan minerals wear away,

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the unfaltering
quartz grains are left

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to pop out of the rock as sand.

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And then it's only a
matter of time, sometimes

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a very long time,
before the quartz sand

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gets whisked away by streams and
rivers and carried to the sea.

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There, at the mouth of a
river, the fast flowing water

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slows abruptly and the
well-rounded sand drops out.

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Larger rocks and pebbles were
already left behind upstream,

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while smaller sediments,
like silt and clay,

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continue to be swept along
by the weakened current

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and are deposited
further from the shore.

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Over thousands and thousands
of years, the paths of rivers

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sweep up and down the coast,
dropping off piles of sand

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to be spread by
waves and currents

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into smooth, sandy beaches.

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Of course, not all beaches
are purely quartz sand

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and not all quartz sand
ends up on beaches.

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But the fact that so many
beaches and so many sands

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are the same is a testament
to the chemistry of the most

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common components of the
Earth's crust as they

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cool and crystallize and
to the physics of sediment,

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slowly shifting and
surging towards the sea.

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They are, quite literally,
the sands of time.

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