Our planet has a layer of atmosphere wrapped around about 15 kilometers thick. This layer of atmosphere consists of nitrogen gas, oxygen, dust, water vapour. and various microorganisms in these gases The most important gas for the existence of Living things on Earth are oxygen gas and the layers of the atmosphere have enough oxygen gas. per life is only 5-6 kilometers thick, which normally has a relatively stable composition of various gases. Our planet has a layer of atmosphere wrapped around about 15 kilometers thick. This layer of atmosphere consists of nitrogen gas, oxygen, dust, water vapour. and various microorganisms in these gases The most important gas for the existence of Living things on Earth are oxygen gas and the layers of the atmosphere have enough oxygen gas. per life is only 5-6 kilometers thick, which normally has a relatively stable composition of various gases. Air pollution is defined as air in which contaminants are present in amounts above normal for long enough to cause harm to humans, animals, plants or property. may occur naturally, such as dust from wind storms Volcanic eruptions, earthquakes, forest fires, natural gas and naturally occurring polluted air are very little harmful to humans.