1. The atmosphere. Composition and structure

The Earth’s atmosphere is a mixture of gases called air.

Air is composed by:

– 78% Nitrogen (N2)

– 21% Oxygen (O2)

– 0,03% Carbon dioxide (CO2)

– 0,97% other gases (water vapour, argon, etc.)

The atmosphere was very different 4600 million years ago. The primitive atmosphere was made up of water vapour, carbon dioxide, nitrogen, hydrogen, and others…

  • Structure

These layers are: the troposphere, the stratosphere, the mesosphere and the thermosphere.

Troposphere Stratosphere Mesosphere Thermosphere
15ºC to -50ºC

(12 km)

-50ºC to -100ºC

(12-50 km)

0ºC to -100ºC

(50-80 km)


-100ºC to 1000ºC

  • Observing the sky

The colours we see in the sky are due to the presence of gases in the atmosphere. The white light that reaches us from the sun is made up of a succession of different colours from red to violet. When the white light from the Sun passes through raindrops we see a rainbow.  (formación del arcoiris)

  1. Pollution, natural enviroment and health

Pollution is the contamination of air, water, or ground by harmful substances. Waste left over from factories pollutes the water and the land. Land pollution may harm animals, plants and soil. These include smog, acid rain, the greenhouse effect, and «holes» in the ozone layer.

The Greenhouse effect (el famoso ‘efecto invernadero’) is the warming of the Earth’s surface and lower atmosphere caused by water vapour, carbon dioxide, and other trace gases in the atmosphere

Global warming (calentamiento global, aumento de la temperatura terrestre) may be due to an increase in the greenhouse effect of the atmosphere. On our planet there is an increase of temperature due to the global warming.

Acid rain (lluvia ácida) is any precipitation that contains a heavy concentration of sulphuric and nitric acids. It is produced when sulphur dioxide and various nitrogen oxides combine with atmospheric moisture. Acid rain can contaminate drinking water, damage vegetation and aquatic life, and erode buildings and monuments.

Ozone depletion (agujero de la capa de ozono) is another result of pollution. Chemicals released by our activities affect the stratosphere, one of the atmospheric layers surrounding the Earth. The ozone layer in the stratosphere protects the Earth from harmful ultraviolet radiation from the sun.

  1. Atmosphere and weather

Weather describes the state of atmospheric conditions at a certain place, over a short period of time. Weather conditions are variable and include:

– Humidity. This is the concentration of water vapour in the atmosphere.

– Clouds. They form when rising air cools.

– Precipitation. This is water that falls to the ground: rain, snow and hail.

-Temperature. This represents how hot or cold the air is.

– Wind. This is air in motion.

Meteorology is the study of different atmospheric variables to make weather predictions. Meteorologists collect information about weather conditions

Climate describes the characteristics pattern of weather in an area, over a long period of time. The climate of a region is expressed in terms of temperature and precipitations. Warm front (frente caliente/templado) occurs when a mass of warm air moves towards a mass of cold air. Cold front (frente frío) occurs when a mass of cold air moves towards a mass of warm air.

Factors affecting climate are:

                -Latitude: It indicates how far north or south a place is from the Equator. The temperature increases from Poles to Equator.

                -Altitude: This is the height above sea level. The higher a place is, the colder it will be.

Distance from the sea: Water heats up and cool down slower than land. The sea keeps coastal areas warmer in winter and cooler in summer.

Ocean currents: they can be warm when they come from tropics or cold, when they come from poles. They make the climate softer

  1. Atmospheric pressure and humidity


Atmospheric pressure decreases when temperature increases. This means that the higher the temperature, the lower the pressure.

Air moves because the Sun heats it.


Air has weight. The pressure it exerts on Earth’s surface is called atmospheric pressure. It is caused by gravity.

Factors provoking variations of pressure:

  • Altitude:

Atmospheric pressure decreases when altitude increases. This means that the higher the altitude, the lower the pressure.

Hot air rises because its density is lower and the colder air moves in to take its place. This is the origin of wind.

  • Low pressure area (depression or cyclone): In depressions, the pressure decreases towards the center. The air, light and hot, moves from down to up. The ascendant air is moist. It provokes unstable weather, because when this water vapour gets colder, it condenses and provokes precipitations.
  • High pressure area (or anticyclone). In anticyclones the pressure increases towards the center. The air, heavy and cold, moves from up to down. The descendant air is dry. It provokes stable weather, because clouds do not form.

The air moves from the areas of high pressure to the areas of lowpressure, causing air currents or winds.


Air contains water vapour because of evaporation (from the surface of seas, lakes and oceans) and transpiration (from living beings, especially plants)

Humidity is the amount of water vapour that the air contains. It varies depending of the place, the time of day and the temperature

  1. Atmospheric phenomena caused by the wind.

A) Wind:

Hurricanes Tornadoes
Hurricanes. These are violent tropical storms that form over the ocean. They consist of a central area (the eye), around which clouds and winds revolve at great speeds (200 km/h) Tornadoes. They start inside large strom clouds and have an inverted cone shape when they leave the clouds and reach the grounds or the sea. These winds can reach speeds of 480 km/h and demolish everything in their path.

B) Due to condensation:

  • Clouds form when air that is charged with water vapour, rises, cools and condenses around tiny dus particles, salt or ash.
  • Fog (niebla) consists of low clouds that form close to the ground. This occurs when the air on the ground cools down but does not go below 0ºC.
  • Frost (helada) forms when the temperature of the Earth’s surface is below 0ºC and water vapour freezes.
  • Dew (punto de rocío) is condensed water vapour. This occurs during the night when temperatures drop

C) Due to precipitation:

  • Rain occurs when the water droplets in a cloud join together. When they are big enough, gravity makes them fall.
  • Snow occurs when the temperature inside a cloud reaches 0ºC. The water droplets freeze. They fall from the cloud when they are heavy enough.
  • Hail (granizo) occurs when there are strong rising air currents inside the cloud which deep freeze the water droplets (-50ºC)

D) Electrical phenomena:

When a storm contains thunder and lightning, it is considered to be a thunderstorm. The action of warm air rising and cold air sinking (convection) plays a key role in the formation of severe thunderstorms. It is at that point that we see lightning and hear thunder. Thunder is the sound caused by rapidly expanding air.


Bounce: reflect back from a surface. (Rebotar)

Damp: moisture in the air. (Humedad)

Depletion: reduce the number or quantity of something. (Disminución) Domed: form a

rounded shape. (Abombado)

Drop: a small round portion of liquid. (Gota)

Flake: a small very thin piece of something. (Copo)

Forecast: predict or estimate. (Pronosticar)

Gust: a strong rush of wind. (Ráfaga)

Hailstone: pellets of frozen rain falling in showers. (Granizo) Harmful: causing or likely to cause harm. (Dañino)

Indoor: situated or used within a building or under cover. (De interior)

Moisture: water or other liquid diffused in a small quantity as vapour.(Humedad)

Release: allow to move or flow freely. (Liberar)

Remove: take off or away from the position occupied. (Eliminar) Rush up: come over in a hurry. (Moverse)

Scarce: insufficient for the demand. (Escaso)

Sinking: go down below a surface. (Descendiendo)

Sticky: hot and humid. (Bochornoso)

Sunrise: the time in the morning when the sun comes up. (Amanecer)

Sunset: the time in the evening when the sun goes down. (Atardecer)

Sweat: moisture exuded through the pores of the skin. (Sudar)