Soil gases are the gases found in the air space between soil components. The primary natural soil gases include N , CO2 and O . The oxygen is critical because it allows for respiration of both plant roots and soil organisms. Other natural soil gases are atmospheric methane and Rn Composition of air in soil and atmosphere: * N : Soil Air: 79.2% Atmosphere: 79.0% * O : Soil Air: 20.6% Atmosphere: 20.9% * CO2 : Soil Air: 0.25% Atmosphere: 0.04% Gas molecules in soil are in continuous thermal motion according to the kinetic theory of gases, there is also collision between molecules - a random walk.