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.