The source of all energy on Earth is the Sun. The agent for all food production on Earth is the life in the soil. To be more accurate, it is the microbial life in the soil. The difference between dirt and soil is that soil has life, hence energy. Living in the soil are countless bacteria, fungi, protozoa and Nematodes. A single gram of soil contains up to a billion bacteria and a million fungi. Most of these microbes live in what is known as topsoil, Topsoil is the upper laye