ABSTRACT

The earth is surrounded by a 80 km thick gaseous envelope known as the atmosphere. There are several different speculations/theories on the origin of the earth’s atmosphere, but it is generally accepted that the atmosphere was created after the earth cooled down. The gas composition was believed to be that of the gases normally emitted by volcanoes. The atmosphere consists of both permanent gases such as nitrogen (78.1%), oxygen (20.9%), argon, neon, helium, krypton and hydrogen, and variable gases including water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Oxygen molecules combine with free oxygen atoms and form ozone, which absorbs ultraviolet radiations from the sun. Some of the variable gases are also known as greenhouse gases that allow sunlight to enter the atmosphere but prevent outgoing ultraviolet radiations from earth, thus trapping the heat and keeping the earth warmer by about 33°C. Soil is a porous media, and gases from the atmosphere enter soil and vice versa, depending on the gas pressure and gradient. Carbon dioxide (CO2) concentrations are usually higher in soil air than in the atmosphere, there can be an order of magnitude difference in CO2 in soil and the atmosphere, and CO2 concentrations are inversely related to the oxygen concentrations in the soil. Similarly, soil air content is inversely related to soil water content.