Soil

Soil is a complex mixture of pulverized rock and decaying organic matter, which covers most of the terrestrial surface of the Earth. Soil not only supports a huge number of organisms below its surface—bacteria, fungi, worms, insects and small mammals, which all play a role in soil formation—but it is essential to all life on Earth. Soil provides a medium in which plants can grow, supporting their roots and providing them with nutrients for growth. Soil filters the sky's precipitation through its many layers, recharging the aquifers and groundwater reserves from which we drink. Slowing the movement of rainfall by absorption, soil prevents damaging floods. By holding air in its pores, soil provides oxygen to plant roots and to the billions of other organisms inhabiting soil. Soil receives and thrives on organic matter as it dies, assuring that it returns to a form useful to subsequent living organisms. Soil has built up over eons on top of bedrock, the solid rock layer that makes up the crust of the earth, as exposed rocks have weathered and eroded and organic matter, including plant and animal life, have decomposed and become part of the soil. The word soil comes from the Latin word for floor, solum.