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)