Topsoil. It's arguably the most precious stuff on earth, sustaining all land-dwelling animals, including humans. It takes nature 500 years to make an inch of it. Until recently, most folks interested in topsoil were farmers and their advisors concerned with how to work it, increase its fertility, maximize its productivity and protect it. But gradually, over the past 20 years, "topsoil" has been transformed into a hot commodity, a multimillion dollar industry responding to demand from homeowners and businesses seeking to establish or improve their landscapes, lawns and gardens. Homes are also going up on steep, barren or rocky sites once considered unbuildable, where the only option for a lawn or garden is to import topsoil.