3.2.1 - The Atmosphere (Full Notes)

3.2.1 – The Atmosphere

 

 

Atmosphere – A thin layer of gases surrounding the Earth that is held in place by gravity

 

 

 

Composition of the Atmosphere: 

 

The Atmosphere is made of 3 main gases with others in trace amounts 

 

Nitrogen (N)

78%

Oxygen (O, O2)

21%

Carbon Dioxide (CO2)

0.04%

Trace Gases combined

1%

Ozone (O3)

0.000007%

 

80% of all gases in the Atmosphere are between the Earth and the Troposphere

 

Natural processes in the Atmosphere are in Dynamic Equilibrium which maintains the average composition so that it only changes over very long timescales

 

Many of these processes are connected, so if one is affected, the others are too. This means that human action can trigger a chain of events where one process causes other process to take place. 

 

 

 

 

 

 

How the Atmosphere supports life:

 

Gases for Natural Processes – 

 

H, N, C and O in the Atmosphere are all needed by biological molecules are used by living processes

 

These gases are extracted from the atmosphere as N2, O2, and H2O. 

 

 

Absorption of electromagnetic radiation – 

 

Much of the biologically damaging radiation from the sun is prevented reaching Earth by the Upper Atmosphere. 

 

Most UV light is stopped reaching the surface by different forms of oxygen in the stratosphere

 

Oxygen is in the atmosphere in 3 different forms. 

O (Monatomic Oxygen)

O2 (Diatomic Oxygen)

O3 (Triatomic Oxygen)

 

Together these 3 forms of oxygen form the ozone layer in the stratosphere which absorbs UV light by producing a dynamic equilibrium of chemical reactions which form and destroy ozone. 

 

O3 molecules are formed when UV hits a diatomic molecule of Oxygen. This splits it into 2 monatomic oxygen molecules. The monatomic oxygen can then bond with other diatomic oxygen molecules to form triatomic oxygen, which is otherwise known as Ozone.

 

There are different types of UV light and different percentages of each are absorbed/ blocked. 

 

UV-a – least energised, least damage, 5% blocked

UV-b – medium energised, medium damage, 95% blocked

UV-c – highly energised, most damage, 100% blocked

 

 

Delaying the escape of IR Energy – 

 

IR keeps our Earth warm, without it the Earths average temperature would be -12

 

Much of the incoming visible light is absorbed and then converted to IR energy. 

 

This raises temperatures in 2 ways

-      The warm atmosphere emits IR which is then absorbed by Earth’s Surface

-      The warm atmosphere reduces heat loss via conduction from land and oceans

 

 

Heat Distribution - 

 

Most of the energy that is absorbed by the Earth’s surface is absorbed at the equator. The warm surface heats the atmosphere above it and then this heat is distributed to higher latitudes by warm winds. 

 

E.g., The South-Westerly winds that bring heat to the UK from the Caribbean Sea

 

 

 

 

 

 

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