Surely chunks of solid earth on which we stand cannot drift easily about the surface of a water body. But floating islands do indeed exist on six of the seven continents and sometimes in the oceans between them. These islands are kept buoyant by the light spongy tissues of certain aquatic plants, by gases released into their soil by decomposing vegetation, or by both these forces.

Floating islands have attracted the attention of ancient authors, and the Roman writer Pliny the Younger has left us an evocative description of the floating islands in Lacus Vadimonis