1) Place a horizontal-facing sticky piston at least 2 blocks off the ground
2) Place a slime block next to the piston such that the sticky piston will push it horizontally when powered
3) Place a dirt block on TOP of the slime block.
4) Rapidly power and unpower the sticky piston over and over again with a redstone torch by placing and breaking it rapidly.
5) Every now and again dublicate dirt blocks will appear out of nowhere.