Sabrina: Thirsty? How about an ice cold glass of dinosaur pee?
Ah! So refreshing. 

(intro)

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?

(Big question)

Remember that water is matter, and matter is made up if particles. As we've learned, the particles can move around, changing states, butting 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 water, 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 3 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. Wan 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 and this tree and a triceratops that lived a long time ago, we're all part of the water cycle too. And that leads us to some pretty crazy ideas. This is were science can get kind of gross. 

Let's look at the water cycle over time. 

(Investigation 2:08)

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 you 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 gotta go. The Brachiosaurus pee hits the ground and pee is, well, mostly water.

The Sun shines down and evaporates that water 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 we're 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 moves 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 flown 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 the puddle of pee, the salt and other impurities get left behind.

(conclusion 4:19)

The particles in you 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.

(endscreen)