Without the natural decomposition of dead organic materials, recycling of the nutrients and the biochemical energy in the carbon contained in organic matter would be slowed dramatically. While periodic fires could rapidly release such energy and nutrients, organic matter production vastly exceeds the scale of the land area for decomposition of organic matter involved in fires. Without this natural decomposition process, dead organic matter would accumulate at the rate of about 15 feet of depth each millennium. Human beings have walked the earth for a million years or so, and plant life has existed much longer. Thus, just since humans began to walk the surface of the earth, dead organic matter in the absence of decomposition would have accumulated to a depth of nearly 3 miles.