If you thought figuring out your neighborhood's recycling pickup was tough, imagine puzzling out how the planet does it. Researchers thought that part of the Earth's upper mantle was made of recycled crust that sunk below the surface in a process called subduction. Now a group has analyzed the chemical composition of a ridge of basalt and glass in the mid-Pacific, formed when lava erupted from the mantle. Although the rock shows signs of being modified by the pressure of subduction, the sunken crust itself is nowhere to be found--it may keep on sinking, the team reported in last week's Nature.