Earth's Atmosphere

The earth is different from the moon in many ways.One of them is that the earth has an atmosphere which causes whether and changes on the planet.For example if you leave a foot print on the moon it will never change and will stay there for ever.On earth it probably wouldn't even last a week because rain or wind or movement would cover it and wash it off.The atmosphere on earth provides air.You might think that air is all oxygen but its only 21%.Air is almost all nitrogen 78% and 1% of other trace gases.