The secret of gliding creatures

The slime that issues out from the earth's ancient, gliding creatures contains a chemical suppressant which maintains, in a state of suspended generation, the hoard of their eggs stored beneath the surface. The eggs remain dormant as long as the parents actively maintain the layer of hormonal slime at the surface. But where this activity is suspended, upon the occurrence of a grand extinguishing event, and the slime layer is dried to chemical inertia, the offspring of the old ones then begin to hatch out. In unimaginable numbers they worm their way upwards.