Water is one of the basic elements of nature and it provides life. Water on Earth is circulated again and again so that it can perform its functions. This phenomenon is called the water cycle. To put it shortly, water moves through the three phases (gas, liquid and solid) over the four spheres (atmosphere, lithosphere, hydrosphere and biosphere) and completes a full cycle. The water cycle is incredibly important:
· it regulates the temperature of the surroundings
· it affects weather and creates rain, snow etc.
· it helps in conversion of rocks to soil
· it circulates important minerals through the spheres
· it creates the many geographical features present on Earth like the ice caps of mountains, icebergs, the rivers and the valleys, lakes, and more
Hence it is quite important so let’s take a look on the water cycle from the point of view of two droplets of water!
How did water get on Earth? We don’t know for sure! Earth was very hot at the beginning of its existence to sustain water. Most probable theory is that water has been delivered to Earth from the outer Solar System by impacts from icy asteroids and comets. Other theory suggests that water got to Earth after the collision with smaller planet that also resulted in creation of Moon.
Our droplet of water, let’s call it Jamall, is swimming with many more other droplets in vast Earth’s ocean. One day, Jamall decides to take a look at the surface to see the Sun. Many friends told Jamall that Sun, if he’s lucky enough, can take him on incredible journeys. So there he goes, as he is slowly reaching the surface, he feels that it’s getting warmer around him.
“That must be the power of Sun, maybe I’ll be one of the chosen!”, he thinks to himself.
And he is right! As Sun shines on the ocean’s surface, the ocean absorbs the energy and turns water into vapours. This is the first step of water cycle and it’s called Evaporation. Evaporation also causes the bodies of water to reduce their temperature.
Jamall feels like he’s being lifted from the ocean. He sees many other droplets still swimming under him as he gets higher and higher! He gets scared at first but then he realizes, he’s not alone, there are millions of other droplets raising with him too!
All the droplets rise up high in the atmosphere. Jamall is suddenly happy! He has never seen Earth from up above, it’s an mesmerizing view. However, he feels it’s getting colder the higher he is.
Jamall looks around and sees how some droplets are starting to freeze.
“What is going on? No one told me about this!”
Some other droplet screams at him “Don’t be afraid, it’s normal, we will become clouds!”
“Clouds?” he asks nervously.
“Yes! You may change the state but it’s still you and you’ll never be alone, it’s called condensation! Come closer and you’ll see!”
The higher parts of the atmosphere have much lower temperatures than are on the surface. Thus, the water that is evaporated from the water bodies is condensed back into liquid or solid and as the small particles get closer together, they form clouds and fogs.
Apart from evaporation, sublimation also contributes to water vapours in the air. Sublimation is a process where ice directly converts into water vapours without converting into liquid water. This phenomenon accelerates when the temperature is low or pressure is high. The main sources of water from sublimation are the ice sheets of the North Pole and the South Pole and the ice caps on the mountains. Sublimation is a rather slower process than evaporation. But let’s go back to see how’s Jamall doing!
“Wow this is amazing! I can see everything! And we are moving so fast!" he shouts enthusiastically.
“Yes, that’s the wind! It can take us everywhere. Wheeeeee!” his new friend is really enjoying the ride on wind.
“Wheeeee!” joins Jamall.“What’s your name?”
“You can call me Joey!”
"I am Jamall!"
This makes Jamall to feel more confident so he decides to get closer to the others and they suddenly follow his lead.
Then Joey asks him: “Wanna see something even more fun?”
“Yes, yes, yes!” he shouts without hesitation.
“Alright chaps” Joey gives order to all the droplets around “it’s time, let’s hold hands!
All the droplets are so close now they appear as one. As enough droplets combine, the gravity starts pulling them down to the surface!
“Aaaaaa…” Jamall screams as the Earth’s surface is getting closer and closer.
“Don’t worry, this is normal too, we are precipitating! Without it, there could not be life!”
The clouds (condensed water vapours) pour down as precipitation due to wind or temperature change. This occurs because the water droplets combine to make bigger droplets. Also when the air cannot hold any more water, it precipitates. At high altitudes the temperature is low and hence the droplets lose their heat energy. These water droplets fall down as rain. If the temperature is very low (below zero degrees Celsius), the water droplets fall as snow. This way, water enters lithosphere.
The impact is so strong the droplets cannot hold each other’s hands and Jamall wakes up on the ground and he feels as it’s sucked underground with others.
As water precipitates, some of it is absorbed by the soil. This water enters into the process of transpiration. Transpiration is similar to evaporation where liquid water is turned into water vapour but it’s done by the plants. The roots of the plants absorb the water and push it toward leaves where it is used for photosynthesis. The extra water is moved out of leaves through stomata (very tiny openings on leaves) as water vapour. Thus water enters the biosphere and exits into gaseous phase.
“That was awesome, let’s do it again!”
Jamall evaporates from the plant’s leaves, condensates in the atmosphere and enjoys free fall with his new buddy Joey back to surface but something is wrong.
“Oh no, I want to fall on some tree!” screams Jamall as he tries to aim on some vegetation.
“You always worry, Jamall. You just never know. Sometimes you can help a flower to survive, sometimes an animal, sometimes you just hit some rock and quickly evaporate back. You know what, come with me and let’s jump into that stream right there.” suggests Joey.
“Okay, I trust you, let’s do it!
So they catch some wind and end up in that tiny stream. This stream takes them to a river. As Jamall and Joey swim freely in the river, more and more droplets join them and suddenly, he’s back in the ocean.
As the water pours down (in whatever form), it leads to runoff. Runoff is the process where water runs over the surface of earth. When the snow melts into water it also leads to runoff. As water runs over the ground it displaces the top soil with it and moves the minerals along with the stream. This runoff combines to form channels and then rivers and ends up into lakes, seas and oceans. Here the water enters hydrosphere.
“Being droplet of water is so cool! Is there anything else we could do? he asks Joey.
“Of course! Follow my lead but don’t be scared!” says Joey in a serious way.
Jamall get’s immediately scared.
“I told you not to get scared all the time, I am with you! However, you should know that where we are heading, there is no light, just darkness but it is important for us to take this journey too! Every droplet eventually does it. I’ll be with you the whole way!”
“Okay” agrees Jamall. He takes a deep breath and dives into the darkness following Joey’s example.
Some of the water that precipitates does not runoff into the rivers, nor is absorbed by the plants, nor gets evaporated. It moves deep into the soil. This is called infiltration. The water seeps down and feeds underground lakes and rivers that can resurface and the whole process of water cycle repeats.
“That wasn’t that bad” says Jamall to his friend when they are evaporated back to the atmosphere through the leaves of one magnificent redwood tree in California.
“Right? I told you so! What do you wanna do next?” asks Joey.
“I don’t know. Does it matter? Let’s just close our eyes and we’ll see where it gets us!”
So, that was a story of two droplets of water going through various types of the water cycle. They might end up in you too! Maybe Jamall and Joey fell in the river that is used as a source of drinking water for your town. Maybe, you drank them, peed them out or maybe they evaporated as a sweat from your armpits. You just never know. Water cycle is an incredibly complex process and life on Earth is dependent on it.
The important thing is that the amount of water on Earth doesn’t change. We are left with the same amount of water since the life on Earth started to evolve. That’s why it’s important to protect it. Humanity is still technologically far from, for example, bringing icy comets from the asteroid belt between Jupiter and Mars as a source of freshwater. Maybe in the future but to get to such a future, we have to protect the water we have right now, life is dependent on it.
Next time, we’ll take a look on the processes that turn the water in lakes and rivers into the drinking water for our homes. See you then!