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You might not see it, but this is probably the strangest thing in the universe.
Here's why.
Every molecule of water on the Earth and inside you or any other living thing has existed for billions of years.
After it came to Earth, that water has been cycling through rocks, air, animals, plants and back again.
Each molecule has been on an incredible voyage before coming to you.
At some point, the water inside you would have been inside dinosaurs, bacteria, the oceans, storm clouds, the polar ice caps and much more.
All of the water on Earth is alien.
They might be a familiar part of our world, but our oceans formed hundreds of millions of years after our planet took shape.
The water arrived on asteroids and comets from space, objects from the edge of our solar system.
They were leftovers of the vast clouds of dust and rocks that didn't quite make it into planets.
This is the origin of all the water you can see on the Earth.
Water doesn't follow the normal rules of chemistry.
For a start, it shouldn't really be a liquid on our planet.
A water molecule is made from two very light atoms, hydrogen and oxygen.
And at the temperatures and pressures on the surface of the Earth, rules of chemistry say that water should be a gas.
And, unlike any other chemical, when water freezes it expands.
And so ice floats on water.
Now you see this every day, but take a moment to think about how weird that is.
Over time, this odd behaviour has been very useful.
By insulating the water underneath, floating ice has enabled complex life to survive and evolve on our planet, despite the many ice ages that have frozen the Earth's surface solid.
And the strangeness just goes on and on.
Did you know that hot water freezes faster than cold?
Yes, really.
No one knows why.
Water molecules can float upwards, against the force of gravity.
That's because they love to stick to each other.
They're so good at it that they can actually pull each other up through tiny channels, such as the tiny blood vessels in your body.
That's how oxygen and nutrients reach the edges of your brain.
The same process, called capillary action, allows plants to move water from deep below the ground to nourish the leaves and branches that grow in the sunshine.
Our solar system is drowning in water.
Once upon a time, we thought that we were alone on Earth with so much water, but in fact it's the second most common molecule in the universe.
We now know there's water on the moon, on Mars, Pluto.
In fact there's H2O on almost every object in our solar system.
And where there's water, there could be life.
So pour yourself a glass of water now, and take a good look at this colourless, featureless and tasteless material.
It's actually remarkable.
It breaks so many rules of chemistry that scientists struggle to understand it.
But without its rebel behaviour, none of us, nor our world, would exist.
You're only here watching this video because water is so strange.



無所不在的「水」,其實超乎想像地怪! (Why water is really, really weird | BBC Ideas)

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Seraya 發佈於 2020 年 5 月 20 日    Seraya 翻譯    adam 審核
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