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Our World of Water

Earth is called the blue planet because it has so much water. Nearly three quarters of the Earth is covered by water and it affects the way our planet works. 

To see how important Antarctica is to the rest of the world we need to look more closely at water.

Water can be found almost anywhere. Water is part of our planet and we could not live without it. 

Water covers nearly three-quarters of the Earth’s surface. It is found on the land, under the ground and in the air. Water can be;

  • fresh (as in lakes, rivers or underground)
  • brackish (as in estuaries)
  • or salty (as in the sea). 

All plants and animals need water. Our bodies have a lot of water in them and we must drink water everyday.

Water affects how our Earth works and looks. 

The weather is affected by water in the oceans, on land and in the air. Water in the form of rain, rivers or glaciers helps to shape our land.

What are some of the things that people use water for?

What is different about water?

Water is the only natural substance that can be found on Earth in all three states;

  • solid – ice
  • liquid – water
  • gas – water vapour

Most substances are denser (heavier) as a solid than as a liquid. For example, a piece of solid candle wax will sink when placed in molten wax.

Water is different. When water freezes into ice, it floats. This is because it is less dense than liquid water - it takes up more space.

It is very important that ice floats. It means that the surface of rivers, lakes and the sea freeze from the top down when it is cold enough. This means animals and plants can live in the water below the ice.

Because ice floats, it is warmed by the Sun and it can melt.

People use water every day and have learnt about how it can change state;

  • water boils at 100 degrees Celsius 
  • water freezes at 0 degrees Celsius

Water dissolves things

Another unusual feature of water is that it can dissolve many things. More things dissolve in water than in any other liquid although, not everything dissolves in water. 

Can you come up with some examples of things which don’t dissolve in water?

Surface tension

Water has a thin elastic layer known as surface tension. Water is unusual because it has the greatest surface tension of any liquid at room temperature other than mercury.

 

 

 

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Nearly three quarters of the Earth's surface is water so it is often called the Blue Planet. Image: NASA: Harrison Schmitt or Ron Evans.

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Only a very small proportion of the world's water is drinkable. Why do you think this is? Image: LEARNZ.

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When water freezes it is less dense so it floats on water. Why do you think this happens? Image: LEARNZ.

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Water is the only natural substance that can be found as a solid, liquid and gas on Earth. Can you see all three states of water in this photo? Image: LEARNZ.

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Water has a thin elastic layer known as surface tension. Image: LEARNZ.

Try floating a large piece of ice or ice cube on water and record your observations.

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