The atmosphere

   1. The atmosphere

   The atmosphere is the gaseous layer that surrounds the Earth. It consists mainly of oxygen and nitrogen. Oxygen is necessary for the respiration of living beings. There are also hydrogen, carbon dioxide, water vapor and other gases. Without the atmosphere, there would be no life on Earth and it would be a dead star as the moon.
We can distinguish three layers:

   - Troposphere (12 km altitude): Almost all atmospheric phenomena such as rain, and wind occur.

   - Stratosphere (12 to 80 km altitude): it has a very cold temperature and there is no wind and rain. The ozone layer varies from 30 to 60 km altitude; it does not allow that the UV radiation enters. If it disappears, there would not be the life on Earth.

   - Ionosphere (80 to 700 km altitude): ions abound because of the solar radiation and they significantly affect the propagation of radio waves.

   2. Choose one of these words and answer: troposphere, stratosphere and ionosphere

It is less than 12 km

It is more than 80 km

It has the Ozone layer

Ions abound

There are atmospheric phenomena

The temperature is very cold

    3. Temperature

   The main atmospheric factors are: temperature, pressure, winds and rain.
People feel heat or cold. This is because the temperature is more or less high in the lower layers of the atmosphere. The temperature is measured with a thermometer. The main variables of temperature are:

   - Latitude: the temperature increases as we approach the Equator and decreases as we approach the poles. In the picture, the yellow zones are warmer than the blue zones.

   - The seasons: Winter is colder and summer is warmer.

   - The sea: Coastal zones are colder in summer and warmer in winter.

   - The relief: the high mountains are colder. From the 4 000 meters high, the region of perpetual snow extends.

   4. Choose one of these variables and answer: latitude, seasons, sea or relief

It is cold when we climb a mountain

It is warmer in summer

The summer is cool near the coast

It is hotter Near Equator

It is cold in winter

It is cold near the Poles



   5. The atmospheric pressure

   It is the weight of air that surrounds the Earth. It is equal to the weight of a column of mercury 765 mm. The areas with high pressure are called anticyclonic and the areas with low pressure cyclonic. The variety is due to these factors:

   - The altitude: The pressure decreases as we climb a mountain. This decrease is so remarkable that causes dizziness, known as altitude sickness.

   - Temperature: the more temperature, the less pressure because hot air expands and it has less density. Cold air has more pressure. The Equator areas, with high temperatures, are areas of low pressure. The polar zones, with low temperature, are zones of high pressure.

   - The Seasons: During winter, pressures are higher than during winter.

   6. Choose one of these words and answer: altitude, temperature or season
 

The pressure is low in summer

There is more pressure in the high mountains

When it is hot, the pressure decreases

Altitude sickness

There is low pressure near Equator

The pressure is higher in winter

   7. Winds

   They are bulk movements of air on the surface of the Earth. These movements are made from high pressure areas to low pressure areas. The anemometer is an instrument for measuring wind speed, and the vane is an instrument for showing the direction of the wind. Winds can be of various types:

   - Prevailing winds: they always blow in the same direction. For Example: the trade winds that always go in the direction of the Equator.

   - Periodic winds: they blow at certain times of year. For Example: the summer monsoon blows from sea to land in Southeast Asia, while the winter monsoon blows from land to sea. The diurnal sea breeze blows from sea to land and the night sea breeze blows from land to sea. (See the picture)

   - Variable winds: they have not a constant direction.

   8. Indicates the type of wind: prevailing, periodic or variable
 

The winter monsoon

They do not have constant direction

The diurnal sea breeze

The trade winds

The summer monsoon

   9. Rains

   When the water of the sea or wetland evaporates, clouds are formed. The water vapor of clouds in contact with the cold air condenses, that is, it goes from vapor to liquid and forms little droplets which fall to earth as rain. When the condensation is at temperatures below zero degrees, the snow is formed.

  10. Flora and vegetation

  Flora is the set of plant species growing in the country, while vegetation is greater or smaller number of plants in a geographical area. The principal types of vegetation are:

   - The forest: there are many trees. When it is very populated and trees are gigantic, it is called virgin forest. This type of forest abounds in the equatorial zone.

   - The Savannah: it is a formation of tall grass in the rainy season.

   - The prairie: with smaller herbs. The savanna and prairie extend by the tropics.

   - The steppe: it is a characteristic of cold and dry climate. It consists of very small and woody herbs, resistant to cold and drought. it abounds in the temperate zones.

   - The desert: without vegetation, except the oasis that has some date palms.

   - The tundra: it is formed by mosses and lichens. It grows in the polar zones./font>

   11. Fauna and animals

   Fauna is the set of animal species living in a region. The animals are distributed in different vegetation zones:

   - Fauna of the forest, formed by monkeys, birds, insects and reptiles that live in the forests and especially in the virgin forest.

   - Fauna of the steppe, savanna and prairie, formed by the horse, antelope and wild animals such as lion, tiger, panther, hyena, etc.

   - Fauna of deserts formed by animals that resist drought as camels and dromedaries.

   - Marine animals formed by the animals that live in the sea.

 
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