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  • Hi, I am Emily from MinuteEarth.

  • And from a distance..

  • The world looks blue and green.

  • And white and kind of yellowish brown.

  • But from a greater distance, it just looks blue.

  • Which makes it unique.

  • It's the only planet that we know of that's covered in liquid water.

  • Coming up four short videos for you, about the weirdness of Earth's water.

  • Let's dive in with the question..

  • "Where did it all come from?"

  • Unlike every other planet in our solar system,

  • Earth's surface is 70% liquid water.

  • Which while useful for life, is also kind of weird.

  • Because everything that we know about how and when our planet formed,

  • says Earth's surface should be bone dry.

  • The story goes like this..

  • Our solar system formed from the collapse of a large cloud of dust and gas.

  • The dense blob of gas at the center ignited to form the Sun.

  • Which as a young unstable star,

  • unleashed a fierce solar wind.

  • Overtime, this stream of charged particles pushed the remaining gas cloud farther and farther out.

  • Leaving only solid particles behind to clump together into rocks, planetesimals, and finally..

  • The rocky planets of the inner solar system that we know today.

  • And here's the problem,

  • water in the form of ice

  • couldn't have been one of the solid particles that stuck around to form our planet.

  • Because the early inner solar system was far too hot for frozen water.

  • And any water vapor would have been blasted away by the solar wind.

  • So if Earth didn't start off with water,

  • how did we end up with such splendid oceans?

  • We know H2O wasn't manufactured here over the eons.

  • Because natural processes like combustion,

  • breathing and photosynthesis,

  • create and destory roughly equal amounts of water.

  • And either way, the amounts in question are so minuscule

  • that they can't account for the abundance of water on the planet.

  • Since Earth's water was neither part of the original package,

  • nor manufactured here.

  • It must have flown in from far away.

  • On meteoroids, or comets or other bodies originating in the outer solar system.

  • Where they were far enough from the Sun for frozen water to survive.

  • The dirty ice balls we called "Comets"

  • are a logical candidate for the source of our water.

  • But we're ruled out when we discover that they were far richer and heavy hydrogen than Earth water.

  • Heavy hydrogen has a neutron as well as a proton in its nucleus.

  • And for every million hydrogen atoms in Earth water,

  • about 150 are heavy ones.

  • While typical comet water has twice that many.

  • These mismatched chemical signatures,

  • suggest that Earth's water couldn't have arrived on comets.

  • It turns out that the most likely source for Earth's water

  • is a type of meteorite called the "Carbonaceous Chondrite".

  • "Chondrite" is just a name given to the class of stony meteoroids that most commonly strike the Earth.

  • But only the Carbonaceous Chondrite contains water.

  • As well as lots of carbon if you couldn't tell from the name.

  • They have water in them because they form out beyond the Sun's Frost Line.

  • And what's more,

  • their water has heavy level of hydrogen similar to that of Earth water.

  • Strongly suggesting that these Earth crashers

  • are the source of our icecaps, clouds, rivers and oceans.

  • And thus, the water that turned our planet into a blue marble

  • came quite literally, out of the blue.

  • Ok, so technically it takes water to make the sky blue.

  • So those first icy comets might not have come literally, out of the blue.

  • But speaking of the sky,

  • a lot of clouds up there look like this.

  • Flat bottom cloud shape top.

  • Why in heaven, do they have that shape?

  • If we wanted to make a cloud entirely from scratch,

  • we'd first need a whole fleet of jumbo jets.

  • Or several hundred hot air balloons, to haul hundreds of tons of water up to the sky.

  • And then, somehow..

  • We need to disperse all that liquid into a mist of droplets

  • small enough to float.

  • In short, it wouldn't be easy.

  • And yet, our atmosphere manages to pump out one cloud after the another

  • all over the world.

  • At altitude of up to 20 kilometers above sea level.

  • Using water and fuel carried all the way from Earth's surface.

  • Cumulus clouds for example,

  • get their start when solar energy evaporates water from oceans, planets and soil.

  • By breaking the bonds that hold water molecules together

  • As the patch of air above collects moisture and heat,

  • cooler, heavier air sinks around it.

  • Pinching it off and pushing it aloft like an invisible hot air balloon.

  • Surprisingly, this balloon's cargo doesn't weigh it down.

  • In fact, the more water vapor it collects before lift off,

  • the lighter it gets.

  • As weird as that sounds,

  • it's because water vapor is a gas.

  • Just like the nitrogen and oxygen that make up most of the atmosphere.

  • Basic physics dictates that a given volume of gas has the same number of molecules

  • regardless of what those molecules are.

  • And water is made of H plus H plus O.

  • Which is lighter than both 2 Ns and 2 Os.

  • So warm humid air is even more buoyant than warm dry air.

  • As the invisible balloon goes up,

  • the falling pressure outside allows it to keep balloon-ing.

  • Which spreads out its internal heat and lowers its temperature.

  • Eventually, the air at the top cools enough for the water vapor there

  • to condense into droplets.

  • Which looked from afar, like a thin wisp of cloud.

  • And as the rest of the balloon rises,

  • water vapor continues to cool and condense at the same altitude.

  • Creating a flat bottomed cloud that appears to grow upward out of nothing.

  • What's more, as the condensing water vapor molecules

  • bond together into liquid droplets.

  • They release the energy they absorbed from Earth's surface when they evaporated.

  • This heats the surrounding pocket of air.

  • Giving it lift and sucking more moist air up behind it.

  • Which cools and condenses and releases heat,

  • which fuels lift and strengthens the updraft.

  • Even in a small Cumulus cloud,

  • the total energy released from condensation is huge.

  • Equivalent to about 270 tons of TNT.

  • And if the supply of water vapor is much larger,

  • the energy released can produce stratosphere high pillars of cloud

  • with violent updrafts, fierce electrical storms,

  • and grapefruit sized hail stones.

  • Not good weather for hot air ballooning.

  • But if you've ever been up in a hot air balloon,

  • or more likely a plane..

  • and gazed down at earth,

  • you may have noticed that a lot of the rivers

  • looked like this.

  • Why?

  • Compared to the white water streams that tumbled down mountain sides..

  • The meandering rivers of the plains

  • may seem tame and lazy.

  • But mountain streams are corralled by the steep walls valleys they carve,

  • their courses are literally set in stone.

  • Out on the open plains,

  • those stony walls give way to soft soil.

  • Allowing rivers to shift their banks

  • and set their own ever changing courses to the sea.

  • Courses that almost never run straight.

  • At least not for long..

  • because all it takes to turn a straight stretch of river into a bendy one

  • is a little disturbance and a lot of time.

  • And in nature, there's plenty of both.

  • Say for example,

  • that a muskrat burrows herself a den

  • in one bank of a stream

  • Her tunnels made for a cozy home,

  • but they also weakened the bank.

  • Which eventually begins to crumple,

  • and slump into the stream

  • Water rushes in to the newly formed hollow,

  • sweeping away loose dirt and making the hollow even hollower.

  • Which lets the water rush a little faster,

  • and sweep away a little more dirt, and so on, and so on..

  • As more of the stream's flow is diverted into the deepening hole on one bank

  • and away from the other side of the channel,

  • the flow there weakens and slows.

  • And since slow moving water can't carry the sand sized particles that fast moving water can,

  • the dirt drops to the bottom and builds up.

  • To make the water there even shallower and slower.

  • And it keeps accumulating until it becomes new land on the inside bank.

  • Meanwhile, the fast moving water near the outside bank

  • sweeps out of the curve with enough momentum to carry it across the channel,

  • and slam it to the other side.

  • Where it starts to carve another curve, and then another, and another, and another

  • The wider the stream, the longer it takes the slingshot-ting current to reach the other side..

  • and the greater the downstream distance to the next curve.

  • In fact, measurements of meandering streams all over the world,

  • revealed a strikingly regular pattern.

  • The length of one S-shaped meander,

  • tends to be about six time the width of a channel.

  • So little tiny meandering streams,

  • tend to look just like miniature versions of their bigger relatives.

  • As long as nothing gets in the way of a river's meandering,

  • its curves will continue to grow curvier and curvier..

  • until they looped around and bumbled them into themselves.

  • When that happens, the river's channel follows the straighter path downhill.

  • Leaving behind a crescent shaped remnant,

  • called an "oxbow lake".

  • Or a "billabong".

  • Or "lago en herradura".

  • Or "bras mort".

  • We have lots of names for these lakes.

  • Since they can occur pretty much anywhere where liquid flows..

  • Or used to..

  • Which brings up an interesting question..

  • What do the martians call them?

  • Okay, so that picture of Mars you just saw..

  • There's something weird about it that we didn't get to the bottom of until after we made that video.

  • Check it out.

  • A little while back,

  • Henry made this great MinutePhysics video

  • about how the weird symmetry of light and shadows on a landscape

  • can make it really hard for your brain to tell which features are popping out

  • and which ones are dented in.

  • Especially if you're not sure where the light is coming from.

  • This reignited an old debate we had here in MinuteEarth.

  • About this photo of the surface of Mars.

  • That sinuses pattern on the landscape is an ancient stream channel,

  • which is cool because it means that liquid water used to flow on Mars.

  • But that crater above it, has a shadow in the top left.

  • Which means that the light in the image must be coming from the top left.

  • Would seems to suggest that the stream channel

  • is actually sticking up above the surrounding landscape.

  • But, that can't be right. Right?

  • I mean river channel should obviously be valleys

  • since they've been carved into the ground.

  • This seems like such a basic fact to me that

  • even when everyone else on my team said they saw this as a ridge.

  • My brain kept telling me it was a valley.

  • It turns out that not only was my brain lying to me.

  • But this stream channel is an example of a really weird geological process

  • that essentially turns landscape inside out.

  • Creating "Inverted Relief".

  • If you live in a cold climate,

  • you may have actually seen something like this happened with compacted footprints in the snow.

  • As the sun melts the fluffier snow around them,

  • they can end up sticking out.

  • Like this..

  • The same thing can happen to a river valley.

  • For instance, say you've got a stream running through a desert.

  • Sometimes, there is so little rain that the stream dries up.

  • As it does, some ground waters actually drawn upward by capillary action.

  • And as it rises and evaporates,

  • dissolved minerals in it are left behind and precipitate out.

  • Coating the sediments at the river bed and cementing them together.

  • As the stream flows and dries up over and over again,

  • more and more cementing accumulates.

  • Making the river bed harder and more resistant to erosion than the surrounding rock.

  • Over the eons,

  • wind erodes that softer rock.

  • Turning the channel into an inverted version of its former self.

  • We can't know exactly how this river bed got turned inside out without

  • getting down on the ground and digging around a little.

  • But we can make some pretty good guesses by studying inverted relief on our home planet.

  • You could even find your own examples on Google Earth.

  • Just be warned that trying to figure out whats right side up and upside down..

  • Will turn your brain inside out.

  • Enjoy your trip down the Google Earth rabbit hole.

  • And thanks for watching.

Hi, I am Emily from MinuteEarth.

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MinuteEarth Explains: Water

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    joey joey posted on 2021/04/30
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