Dirt is something you wash off or vacuum up; you want it to go away. Dirt is inert, it's lifeless. Soil, on the other hand, you hope stays in place; it is teeming with life. Soils are complex, fascinating ecosystems. Soil scientists have identified over 100,000 different soil types around the world. One trait all soils share is that they are the primary source of the food that sustains life on Earth: plants. An Iowa Beef Council bumper sticker reads, "The West Wasn't Won On A Salad." One might argue whether the West was actually "won" or not, but for sure the steaks that early settlers were eating came from cows that ate salad: plants that grew in the soil. Most life on Earth would not be possible without soil. It is as important to life as air and water.
From Mark Muller's "The World Beneath Your Feet: A Closer Look at Soil and Roots," Funded by the Iowa Living Roadway Trust Fund