As a sustainable and renewable energy resource, biomass is constantly being formed by the interaction of CO2, air, water, soil, and sunlight with plants and animals. After an organism dies, microorganisms break down biomass into elementary constituent parts like H2O, CO2, and its potential energy. Because the carbon dioxide, a biomass releases through the action of microorganisms or combustion was absorbed by it in the recent past, biomass combustion does not increase the total CO2 inventory of the Earth. It is thus called greenhouse gas neutral or GHG neutral. Common sources of biomass are: