Dirt is one of the most common blocks on the surfaces of maps. Dirt/Grass is required for plants like Saplings to grow. Dirt doesn't fall when there are no blocks under it so its useful for creating building foundations. Grass grows ontop of Dirt if it has sunlight falling on it and a Grass block next to it. When Dirt is destroyed Dirt is dropped, there is also a small chance that a Bone will be dropped.