It's right beneath our feet, rarely thought about, but it can be quite useful, destructive, or even used in sport. Add water and it takes on a sticky form. -- Lloyd Young ( 42 photos )

Revelers participate in the traditional Bloco da Lama (Mud block) carnival in Parati, Rio de Janeiro State, Brazil, on Feb. 9. The event, which was begun by two men in a playful manner in 1986, has now become a traditional carnival in which participants disguised as primitives with rags, lianas or skulls and bones, dive in the mud. (Victor Moriyama/AFP/Getty Images)