The Hollow Earth hypothesis proposes that the planet Earth is either entirely hollow or otherwise contains a substantial interior space. The hypothesis has been shown to be wrong by observational evidence, as well as by the modern understanding of planet formation; the scientific community has dismissed the notion since at least the late 18th century. The concept of a hollow Earth still recurs in folklore and as the premise for subterranean fiction, a subgenre of adventure fiction. It is also featured in some present-day pseudoscientific and conspiracy theories.
