[tag=RB] □ □ □
[tag=RB] □ □ □ □
[tag=RB] □? □ □
At this site , Earth 's outer shell is pulling apart , allowing molten rock to rise close to the surface and feed hydrothermal springs . Then it sinks back to the surface and starts the loop again . The tube would also send soil samples back to the surface and carry power to the robotic mole .