Sid tells Manny and Diego that the floor is hot. They find out that they're walking on a bed of igneous rock when the volcano erupts. They have a few close calls but all manage to escape to safety.

Bill Nye explains about sedimentary, igneous and metamorphic rocks and the rock cycle.

The narrator explains how sedimentary rocks form: from sediment deposited in water through the process of weathering and erosion. He also explains the layers of sedimentary rock, which include sandstone, limestone, and conglomerates.

Trevor, Anna and Sean are stuck inside an active volcano. Their only hope to escape is to start an eruption that will propel them out of the volcano. On his last flare, Trevor finally lights a spark between two igneous rocks in the wall to begin the eruption.

The Doctor shows Donna an unforgettable sight of how the rocks in space formed our solar system 4.6 billion years ago.