Samplers from NASA on October 5, 2005 are testing why atmosphere on Mars is so different than on Earth. Researchers believe that causes of atmosphere on Mars are mainly volcanoes. Volcano eruptions will release carbon dioxide, and the volcanoes are common and constant on Mars. On Earth the rain will wash the carbon dioxide away. Not only does Mars not have rain it also has way bigger volcanoes causing more carbon dioxide to be released. -
Other reasons aren't as major for instance, planetary formation from the solar nebula, out gassing from material on the planetary surface, vaporization of impacting comets, release of gases from deep inside the main body through volcanoes and vents and last of all bi-products of biological and man-made processes. For the vaporization of impacting comets some interesting things are they found some of the comets in Antarctic with signs of the gases found inside are similar to the gases found in Mars' atmosphere.
Because there is so much carbon dioxide on Mars the clouds sometimes are made with carbon dioxide instead of Oxygen and water vapor. Also the gravitational pull holds down the atmosphere. If it didn't we may not have as much oxygen. "If Mars has no more volcanic eruptions, I might live there." Says Greg Walker.
The Earth and Mars have different atmospheres because there are so many different ways of producing the atmosphere. However because of our different ways of producing atmosphere we obviously aren't unified, causing different weather. As all people know the atmosphere is made up of lots of composed gases.
On the left you'll see the amount of each type of gas on Earth and on Mars. Surprisingly the planet's gases differ by a lot.