A changing Atmosphere

The present atmosphere mostly consists of Nitrogen(78%), the second gas is Oxygen(21%) and the remainder was 0.9% Argon, 0.04% Carbon Dioxide. There are also traces of other gases.

The Early atmosphere was almost all carbon dioxide when the Earth was formed. It has decreased to approximately 0.04% (the present percentage). Some of the carbon dioside dissolved into oceans. Some marine animals used this dissolved carbon dioxide to make calcium carbonate for their shells. When they die, these marine animals fell to the sea bed and then their shelss eventually formed limestone. The carbon that as locked up in the limestone, originally came from the atmosphere.

Changes in the Atmosphere:

The composition of the Earth's atmospher now is not constant. It can be changed by human activity There are also natural causes of changin gin the atmosphere: Questions to ask myself:
 * Burning fossil fuels release carbon dioxide into the atmosphere. Sulfur dioxide can also be release, if there is inpurities in burning coal
 * Farming affect the composition of the atmosphere, as cattle and rice fields release methan.
 * Deforestation can also add carbon dioxide to the (air)atmosphere, if the trees are burnt. Ther are fewer trees which means that fewer trees are able to absorb carbon dioxide from the atmosphere.
 * Volanoes emit sulfur dioxide and carbon dioxide when they erupt.

Name two reasons why carbon dioxide decreased in the atmosphere?

Name two reasons why carbon dioxide as increases in the present atmosphere: