What happens when you put bits and pieces of rocks and minerals, grass clippings, fruit and vegetable trimmings and peels, fallen leaves, twigs, water, oxygen, and a handful of worms in a compost bin? After several weeks, you should end up with a uniform, dark brown, crumbly product with an earthy aroma—soil.

Soil is a loose mixture of weathered and eroded rock particles, organic matter, mineral fragments, water, and air. It covers much of the land surface on Earth. This complex mixture is essential to life on the planet; all living organisms are connected to soil in one way or another. It supports a wide range of organisms—from microorganisms to massive stands of redwoods. In addition, humans depend on soil to provide stability for building structures, grow fruits and vegetables, sustain livestock, and act as a natural water purification system.