UNIT 3. AIR AND WATER (3º E.P.)

-UNIT 3 – AIR AND WATER

THE ATMOSPHERE

What is the atmosphere?

The atmosphere is made of air and other elements such as water vapour.

Air is a mixture of different gases:

• Nitrogen.

• Oxygen.

• Carbon dioxide (small amounts) and other gases.

Atmospheric phenomena

The atmospheric phenomena are the changes of the atmosphere. Some examples are: wind, cloud, precipitation.

-      The Sun heats liquid water and it turns into water vapour.

-      Clouds form when the water vapour in the atmosphere gets cold and turns into liquid water (drops).

-       Precipitation: when the drops of water in the clouds are too big they fall rain. If the droops freeze as balls of ice, they fall as hail. If the drops freeze as crystals of ice, they fall as snow.

-      Wind: there is wind when The Sun heats the air and it moves.

Atmospheric pollution

Human beings cause damage to the atmosphere. This is called atmospheric pollution:

-      Smoke and poisonous gases from factories, cars.

-      Polluted air is dangerous for human beings to breathe.

-      Polluted water vapour that falls to The Earth as rain and snow can be dangerous for our health and the planet.

THE HYDROSPHERE: THE WATER ON EARTH

The water on Earth

There are two types of water:

• Surface water: oceans, seas, rivers, lakes, ice and snow. There is also water in clouds.

• Underground water: is water under the surface of The Earth.

Salt water and fresh water

There are two types of Surface water:

• Salt water is water that contains lots of salt (in the seas and oceans).

• Fresh water is water that contains little salt (in rivers, lakes and underground).

We use water

Human beings need to drink water. But we also use water

• at home: to drink, to cook, to wash ourselves, to water plants at home.

• in agriculture and farming: to water the crops and for animals to drink.

• in towns and cities: to water gardens, clean streets and buildings, to fill swimming pools…

• in industry: to make things, clean factories and machines.

THE WATER CYCLE

The changing states of water

Because of the heat of The Sun, water continuously changes its state in nature:

• Evaporation: The Sun heats the water and it becomes water vapour in the atmosphere.

• Condensation: The water vapour cools down and forms drops of water which become clouds. The drops fall as rain.

• Solidification: When the drops of water in the clouds are very cold they become ice. They fall as snow and hail.

• Melting: The Sun heats the snow and ice and it becomes liquid water.

What is the water cycle?

The water cycle is the movement of water through the hydrosphere, the atmosphere and The Earth’s crust.

There are four stages:

• The Sun heats the liquid water on the surface of The Earth; the water evaporates and the water vapour in the atmosphere.

• Water vapour condenses and form clouds.

• The water in the clouds falls to the ground as precipitation (rain, snow and hail).

• Water runs across The Earth’s surface or infiltrates it.

The cycle starts again.