Dr. Universe

Dear Dr. Universe: Where does dirt come from? - Brian, student from Pullman, Wash.

In just a word, the story of soil goes something like this: “CLORPT!” It’s fun to say, and it helps explain how tough rock turns into the soft soil farmers need to grow food and feed the world.

Jim Harsh is a scientist at Washington State University and an expert on soil. He said a soil scientist, Hans Jenny, came up with five actors in the soil story: CLimate, Organisms, Relief, Parent material, and Time.

The texture, smell, and color of soil can often depend on the type of climate where the soil formed. Up in...