The atmosphere that surrounds our planet Earth contains the right proportions of gases that are absolutely essential for life, one of those gases is oxygen, making up 21 percent of the air we breathe, without it humans and animals die within minutes. But too some of those gases, by themselves are deadly but because air contains safe proportions of these gases, we can breathe them without harm.

Layers of the atmosphere via Wikipedia

Oxygen making up 21 percent of the air we breathe the right proportion, much oxygen becomes toxic if breathed too long, if there were too much oxygen in the atmosphere combustible materials would become highly flammable, fires would easily burst forth and would be difficult to control.

Other of these gases is Nitrogen, making up 78 percent of the air we breathe. Oxygen is diluted with Nitrogen, but Nitrogen is much more that just a dilutant, during thunderstorms and lightning causes some Nitrogen to combine with oxygen, the compounds produced are carried to the Earth by rain, and plants make use of them as fertilizer.

Other of those gases that our atmosphere contains is Carbon Dioxide, makes up less than one percent. Without it, plant life would die, plants need to take in, giving off Oxygen in return. A decreasing percentage of Carbon Dioxide could not support plant life, an increase percentage of carbon Dioxide in the atmosphere would to be harmful to humans and animals, that small amount of less than one percent of Carbon Dioxide in the atmosphere is that plants and animals need to exist.

In addition the atmosphere shields the Earth from bombardment by meteors. Most meteors never reach the ground because they burn up in their descent through the atmosphere. Our atmosphere serves as a protective shell, a thin layer of Ozone gas filters out harmful radiation from the sun, about 15 miles above the ground. Without this Ozone layer, such radiation could destroy life on Earth. In conclusion the atmosphere is of great importance to protect our existence in our planet Earth.