Thirsty? How about a nice cold glass...
of dinosaur pee?
Ah, so refreshing!
[INTRO MUSIC]
Okay, let me explain.
Last time we learned all about the water cycle.
Water circulates around the Earth, going from a liquid to
a gas (and occasionally to a solid) over and over again.
And while I was babbling on about the water
cycle, you may have noticed something.
Water never leaves the system,
and new water never comes in.
That makes water a limited resource.
There's only a certain amount of it on Earth – no
more and no less, and that amount never changes.
So, what does it mean when we say
that water is a limited resource?
Remember that water is matter,
and matter is made up of particles.
As we've learned, the particles can move around;
changing states, buddying up with other particle friends,
but new particles can't be created from
nothing, and they can't be totally destroyed.
This is called the conservation of matter.
Since water keeps cycling over and over again
on our planet without adding or removing matter,
we say it's a closed system.
Well, it's a mostly closed system;
teensy amounts can leak out into space and whatnot.
But, for our purposes, let's assume it's closed.
Now, if you were paying super close attention last time,
you may have noticed that we only talked
about three of the Earth's four spheres.
We talked about how water – the hydrosphere –
interacts with the geosphere in liquid form,
and the atmosphere in vapor form.
Can you tell which one we missed?
You're looking at it!
Me, and you, and us!
We're both members of the biosphere.
That means me, and you, and my cat in this tree,
and that triceratops that lived a long time ago...
we're all part of the water cycle, too!
And that leads to some pretty crazy ideas –
this is where science can get kind of... gross.
Let's look at the water cycle over time.
Water has been on the Earth almost
as long as there has been an Earth.
Scientists aren't sure how it got here in the first place, but we know that it's here, and it's not going anywhere.
That means the water coming out of your faucet is old...
really old.
I'm talking older-than-dinosaurs old.
Take this thirsty brachiosaurus over here.
He stops at a stream for a long drink,
He moves about his day doing dinosaur
things, hanging out with his dinosaur friends,
until nature calls – he's got to go!
The brachiosaurus pee hits the ground,
and pee is, well... mostly water.
The Sun shines down and evaporates that
water in the pee, turning it into water vapor,
while the salt and other minerals
are left behind on the soil.
The water vapor rises into the atmosphere,
mixes with other water vapor,
and cools enough to condense into a cloud.
Then the wind may move the cloud
to a whole different part of the world.
Eventually, gravity will pull the water
back to the ground as precipitation.
Keep in mind: the dinosaur pee, just like
all matter, is made up of lots of particles.
As they move together through the water cycle,
the particles that were all together in our Brachiosaurus
pee get all mixed up with other water particles
that have been on different journeys.
But, since the Earth only has a
limited number of total water particles,
these little guys move through
the water cycle again and again.
So, some of the dinosaur pee water particles might
have spent thousands of years locked in glacier ice.
Some of them passed through many more dinosaurs.
Some flowed through the Nile River as the ancient Egyptians were building the pyramids.
Some hydrated a giant Redwood tree!
Some quenched the thirst of George Washington!
And some of those particles eventually became...
you guessed it, his pee!
You could be drinking George 
Washington's pee. Or his sweat. Or his tears.
The good news, though, is that as water
moves through the cycle, nature cleans it.
The water cycle takes salty,
undrinkable water from the ocean,
and turns it into the glorious,
refreshing, drinkable drink we all enjoy!
That's because when water is evaporated
from the ocean, or from a puddle of pee,
the salt and other impurities get left behind.
The particles in your drinking water
would have some crazy stories to tell!
But one thing's for certain:
since water is a limited resource in a closed system...
some of the particles definitely
passed through a dinosaur!
[OUTRO MUSIC]
