The extraordinary notion that an entire planet might be alive or even conscious has been explored in fiction, philosophy, and science. One of the first stories based on this theme was Conan Doyle's "When the Earth Screamed" (1929) in which a deep shaft is drilled through the crust to expose the planet's supposed living flesh. According to the controversial Gaia hypothesis, the biosphere of Earth can be considered to act as a single integrated life-form. Among those to develop fictionally the idea of intelligent and conscious worlds are Olaf Stapledon in Star Maker, Stanislaw Lem in Solaris, and David Brin in Earth (1990). In Piers Anthony's novel Chthon (1967), a geologically complex prison planet is described as a 'mineral intellect;' it communicates with other planets across the galaxy, hates humans, and plays a central role in the plot.