Natural factors that have changed the Earth’s atmosphere

Theories suggest that the Earth formed 4500 million years ago.  Its first atmosphere mainly consisted of hydrogen and helium gases.  These gasses are light and would have been lost to space.  As the Earth cooled, the surface formed a crust, this crust was made up of plates containing many volcanoes.  The gasses expelled by volcanic activity formed the next (early) atmosphere of the Earth.  This atmosphere consistent of:

The Earth’s atmosphere would also have contained water vapour.  Over the next few billion years the following processes occurred:

• The surface of the Earth cooled and volcanic activity became less, the water vapour in the atmosphere condensed forming seas and oceans.  This allowed living organisms to form as the water absorbed harmful UV rays from the sun.
• Carbon dioxide dissolved in the seas, it dissolved in falling rain forming carbonic acid, and this reacted with minerals in the Earth’s crust forming carbonates.  Some of these carbonates would eventually be washed into the seas.
• The first living organisms were bacteria.  Nitrifying bacteria used the ammonia from the atmosphere in order to grow, producing nitrates on the surface and in soil as a result.  Denitrifying bacteria used the ammonia from the atmosphere in order to grow, releasing nitrogen gas into the atmosphere as a result.
• Green plants were able to grow in these nitrated soils.  Using up carbon dioxide and water in the process of photosynthesis, producing oxygen gas.
• This oxygen gas reacted with elements producing oxides.  It reacted with ammonia in the atmosphere producing nitrogen and water, it reacted with methane in the atmosphere producing carbon dioxide and water.
• As oxygen levels increased, it reacted in the upper atmosphere forming ozone, a chemical which absorbs harmful UV rays.  This allowed animals to develop on the Earth’s surface.

The current atmosphere has been relatively steady for the last 200 million years

• Nitrogen, N₂ – 78%
• Oxygen, O₂ – 21%
• Other gases, including carbon dioxide, argon, water vapour and other Noble gases make up 1%.

Whilst the atmosphere has remained constant over recent times, natural occurrences such as volcanic eruptions can alter the balance slightly.  In the last decade there have been notable volcanic eruptions in Iceland and Japan that have effected the environment and populations in the area.

Iceland - http://europe.newsweek.com/iceland-experiencing-its-biggest-continuous-volcanic-eruption-centuries-277733?rm=eu

Iceland - http://news.bbc.co.uk/1/hi/world/europe/8634944.stm

Japan - http://europe.newsweek.com/photos-rescue-mission-japanese-volcano-mount-ontake-stops-274108

Volcanic eruptions can affect the Earth's atmosphere in a number of ways:

• It increases the acidity of rain as carbon dioxide and sulfur dioxide released from the volcano dissolve in rain water,
• It can cool the Earth's atmosphere as the ash and dust particles in the atmosphere reflect some sunlight meaning the heat doesn't reach the Earth's surface.