Beneath the surface, moisture started pouring into the corpse. First, after a few days of rain, the soil saturated, the wooden box began to warp. And mud and worms and the occasional critter discovered this tasty trove. And they ate of its meaty parts. And the they defecated on the corpse. And soon, what was still left of the corpse was plump and crawling with bacteria. The eyes fell apart and holes opened up throughout the torso exposing the empty cavity where the organs had once lived. Nothing went to waste, some was eaten and what was not simply decayed more and more until it was no longer flesh, or goo, but soil. And this was the story of all pieces of this once-was person, from being to corpse, to goo, to ooze, to soil. The bones took much longer. And trees pushed roots through the cavity to disassemble the skeleton until no recognizable order could be found.
Eventually, nothing was left except fertile soil and compost. And that was that.