"We stand, in most places on earth, only six inches from desolation, for that is the thickness of the topsoil layer upon which the entire life of the planet depends." R. Neil Sampson in Farmland or Wasteland: A Time to Choose

One of my interests, dating back 25 years to when I was a member of my local FFA land judging team, is soil conservation. I have long been interested in things like terra preta and composting because of their ability to build topsoil. But I never thought much about how difficult it can be to build up topsoil until I read Kim Stanley Robinson's Mars Trilogy - Red Mars, Green Mars and Blue Mars (great books, by the way). The books trace a future hypothetical terraforming of Mars, and one of the major difficulties the characters face is producing topsoil on the planet. It was then that my interest in the mechanisms for topsoil erosion and topsoil production greatly increased.