yego.me
💡 Stop wasting time. Read Youtube instead of watch. Download Chrome Extension

The water cycle | Weather and climate | Middle school Earth and space science | Khan Academy


3m read
·Nov 10, 2024

Did you know that the water you drink is actually the same water that dinosaurs drank over 65 million years ago? It might be hard to believe, but your water is actually really, really old. In fact, water on Earth is much older than the dinosaurs. Scientists estimate that the water on Earth is at least 4.6 billion years old.

The amount of water on Earth today—in lakes, rivers, oceans, glaciers, even under the ground and up in the clouds—it's about the same as it was millions and millions of years ago. That's because water is recycled; it just gets used again and again. And that brings us to the water cycle, which is how water continuously moves from the ground to the atmosphere and back again.

As water moves through the cycle, it changes form. In fact, water is the only substance on Earth that naturally exists in three states: solid, liquid, and gas. Have you seen water in all of its different states? Maybe on a hot day, you'll add some ice—which is water in its solid state—to a glass of liquid water. Or maybe when you take out some food that you've heated in the microwave, you'll see steam coming off of the food, which is water in its gas state as water vapor.

When you think of water, you might think of the wide open ocean. Over 95% of all the water on Earth is in the ocean, so this is a great place to start with the water cycle. Here, energy from the sun warms up water on the surface of the ocean enough to turn it into water vapor. This is called evaporation. This water vapor is less dense, meaning it's lighter than liquid water, so it rises up and up into the atmosphere.

However, as the water vapor rises, the temperature in the atmosphere cools. In turn, the water vapor condenses into tiny liquid water droplets, or as we see them, clouds. This is called condensation. Air currents then move these clouds all around the Earth. As a cloud collects more and more liquid water droplets, the water may be released from the cloud, pulled down by gravity, and then returned to the ocean or land as precipitation, like rain.

If it's really cold, though, the water drops may crystallize and become snow. The snow will fall to the ground and eventually melt back into a liquid and run off into a lake or river, pulled down by gravity, which flows back into the ocean where the whole process starts over again.

But that's just one path water can take through the water cycle. It's like a choose your own adventure. Instead of snow melting and running off into a river, the snow could become part of an icy cold glacier and stay there for a long, long time, for thousands of years. Or rain can seep into the ground and become groundwater, where it's then absorbed by plant roots.

In turn, through transpiration, the water absorbed by the plants can transition to water vapor and leave directly through the leaves via tiny holes called stomata and return to the atmosphere. Or instead of being absorbed by plant roots, the groundwater can work its way to an underground aquifer or a lake, river, or even the ocean.

There are many different paths for water, and the water cycle can be very complicated. But it really comes down to something very simple: the amount of water on Earth stays pretty constant over time and moves from place to place, sometimes transitioning between phases depending on things like weather, geography, solar energy, and gravity.

Now, we know that water is essential to life on Earth, and freshwater is an especially limited resource for a growing world population. Changes in the water cycle can impact everyone through the economy, energy production, health, recreation, transportation, agriculture, and, of course, drinking water.

That's why understanding the water cycle is so important. That, and it's pretty cool to know that you drink the same water as dinosaurs did. Until next time!

More Articles

View All
Scaling functions introduction | Transformations of functions | Algebra 2 | Khan Academy
So this is a screenshot of Desmos. It’s an online graphing calculator. What we’re going to do is use it to understand how we can go about scaling functions, and I encourage you to go to Desmos and try it on your own, either during this video or after. Le…
From the Ashes - Official Film Trailer | National Geographic
[Music] Ralph Waldo Emerson wrote, “Coal is civilization and power.” From the early 1900s to World War II, coal powered America. We’re still quite dependent on coal, but coal was a nineteenth-century source of fuel, and we’re in the 21st century. The tow…
Diode
The diode is our first semiconductor device, and it’s a really important one. Every other semiconductor is basically made from combinations of diodes. Here’s a picture of a diode that you can buy. This is just a small little glass package, and that distan…
Diving With Bullsharks | World's Biggest Bullshark
Neil and James search a shipwreck for the mega shark, Big Bull, and other large bull sharks that may be her descendants. “I’m good over here,” Neil says. Bull sharks have a pack-like mentality and swarm around possible food. They surround the divers. Ne…
15 Traits of a Bad Life (2023)
If yesterday we talked about the good life, it just makes sense to look at the other side of the coin. The worst thing one can do is reach the end of their existence and realize they never lived; they were just alive. Along the way, by the end of this vid…
Homeroom with Sal & Melinda Gates - Tuesday, January 12
Hi everyone, Sal here from Khan Academy. Welcome to the Homeroom live stream! Actually, I think this is the first of the year. Hopefully, everyone had a good New Year’s considering the circumstances and is enjoying 2021. Given the circumstances, we have a…