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
Multi step subtraction word problem
We’re told that a train traveling through Japan has 90 passengers. 52 passengers get off in Tokyo. In Kobe, another 29 passengers get off the train. No new passengers get on the train, and then they ask us how many passengers are still on the train. Paus…
Rare Footage: Wild Elephants “Mourn” Their Dead | National Geographic
I was pretty amazed by this scene when we came across it. You know, you do hear these stories about elephants showing this really keen interest in dead bodies of their species, and it’s just a very hard thing to observe. So, to find a body to begin with i…
Introduction to Grammar | Grammar | Khan Academy
Hi everyone, my name is David and I’m here to introduce you to grammar on Con Academy. Welcome! I’m so glad you could join me. So let’s start by asking the question: What is grammar? What is this thing? Why is it worthwhile to study it? Why would you wan…
Teaching Social Studies with Khanmigo
Hi, I’m Michelle, a professional learning specialist here at KH Academy and a former classroom teacher just like you. Meet K Migo, your AI-driven companion who’s revolutionizing teaching for a more engaging and efficient experience. Kigo has many exciting…
Turning Gourds Into Storage | Live Free or Die: How to Homestead
In this life, I need containers of all kinds. One of the biggest, most frustrating things for me is mice getting in my stuff. It drives me crazy! I really need a container that I can put the cattail fluff in that I use for my Tinder bundles. A friend of …
Horses vs. Horsepower: Watch Historic Rides Race Each Other | National Geographic
History is important, and we get hundred-year-old vehicles out and run. We feel that the educational aspect of someone being able to see these cars in motion is well beyond what someone would learn simply by watching the cars in a museum. Welcome to Race…