Unit 3: The hydrosphere                                                    1   2   3   4   5

 

 

1. The water on the Earth

The Earth is the only planet in the solar system that has surface water: three quarters of the Earth is covered with water.

 

The water on the Earth's surface is called the hydrosphere.

 

Water on the Earth is found mainly in liquid state, but it also exists as ice and water vapour. It is distributed in this way:

 

   - 97 % Oceans and seas. It is salt water.

 

   - 3% Poles, glaciers, lakes, rivers, groundwater,

     clouds and living beings. It is fresh water.

a) Origin of the hydrosphere

 

The Earth’s hydrosphere has two origins:

 

  - In the primitive Earth there was an intense volcanic activity that

    released great amounts of water vapour in the primitive atmosphere.

    This water vapour condensed and became rainfall as the planet

    slowly cooled down and created the oceans.

 

  - Comets and asteroids entering the Earth's atmosphere also

    contributed to increase the amount of water in these primitive

    oceans.

 

 Animación: Origen de la hidrosfera (SM)

 

b) Properties of water

 

Water is a substance with unique properties. It plays an important part in the geological processes that occur on the Earth's surface and is essential to living beings.

 

The main properties of water are:

 

- Water is a very good solvent

 

It is used in many life functions. For example, blood contains  water and transports dissolved nutrients and waste products. Plants can only absorb nutritive substances if they are dissolved in water.

 

On the other hand, it dissolves many components of rock.  

When water evaporates, it leaves deposits of mineral salts.

 

- Water has a high thermal capacity.

 

This means that it heats up and cools down slowly, so that water regulates temperature and moderates the Earth's climate.

 

Many living beings also used water to regulate their body temperature. Sweating is the mechanism that allows them does it.

 

- Water reaches its maximum density in a liquid state at 4°C.

 

Unlike other liquids, water is less dense and has more volume in a solid state (ice) than in a liquid state. This is important for aquatic living things: when the temperature drops and ice forms, the ice floats on top of the liquid water, which means life can continue below the ice.

 

Animación: Las propiedades del agua (SM)

 

READING ACTIVITIES

 

After reading the text, copy and answer the following questions into your notebook:

Remember: you must make complete sentences.

 

1.1. Look at the diagram on the text about the distribution of water

        on the Earth and answer:

      a. What percentage of water is in oceans? What percentage represents

          fresh water?

      b. What percentage of fresh water is at disposal of living beings?

          What part of it is accumulated as ice and ground water?

      c. What percentage forms part of living beings?

1.2. Listen and indicate if the following senteces are true of false:


1.3.    What relationship is there between volcanic activity and the hydrosphere?

 

1.4.    Answer these questions about the properties of water:

       a. When a lake freezes in winter, why does the ice layer float

           on the surface of the water?

       b. Why is water a good regulator of temperature?

       c. Why is water a good medium to transport substances for living beings?

 

1.5. Listen and indicate what property of water is related to each sentence:

a. Good solvent

b. High thermal capability

c. Maximun density in liquid state


 

Now,

check

your

answers!

1. The water on the Earth (answer key).p
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