Humans are doing alot of damage to our soil through strip mining, mountaintop removal, pollution, bad agricultural practices and other activities that promote erosion. Humans are killing the soil and letting it be carried away by the wind or washed into the sea. it takes 100 years to make top soil, and the world is losing 25 billion tons of topsoil a year due to erosion, with the US letting its soil be eroded at a rate 10 - 17 times faster then it could be made. As dirt the movie points out, much of human history has been a struggle over who has productive soil. If humans allow this most precious resource to be destroyed or lost, we can't mine more or travel to another planet to get some.