|Location:||Sol system, Sector ZZ9 Plural Z Alpha|
|Main lifeforms:||Mice, dolphins, humans|
Earth, also known as Sol III, was a giant supercomputer designed to find the Ultimate Question of Life, the Universe and Everything. Designed by Deep Thought and built by the Magratheans, it was commonly mistaken for a planet, especially by the ape descendants who lived on it. It was situated far out in the uncharted backwaters of the unfashionable end of the Western Spiral Arm of the Galaxy.
Unfortunately, the Earth was destroyed by the Vogons five minutes before the program was to be completed. The Vogons were sent by the psychiatrist Gag Halfrunt, who thought his profession would cease if the Question were known. Later on, the Earth reappeared but all forms of the Earth were later demolished.
Earth was mainly populated by "ape-descended life forms" or Humans, which number around 6.5 billion at the time of the earth's destruction. The earth is also inhabited by a series of flora and fauna, including the mice and dolphins, the most and second most intelligent species on the supercomputer respectively, with humans being the third.
Humans do not realize they are only the third most intelligent and are among the most ignorant and technologically backward people in the universe.
- “A computer of such infinite and subtle complexity that organic life itself shall form part of its operational matrix.”
- —Deep Thought on the Earth.[src]
When the supercomputer Deep Thought announced the Ultimate Answer as Forty-Two after seven and a half million years of thought, it challenged Phouchg and Loonquawl to say what the Ultimate Question actually was. When they could not, Deep Thought designed a supercomputer that could give the Question, giving it its future name of the Earth.
The Magratheans were then hired to build the Earth, using a method of sucking matter through white holes to construct the vast planet-like computer. Slartibartfast designed the fjords of Norway, for which he won an award.
The psychiatrist Gag Halfrunt thought that his career would cease if the Question were known. Therefore he got the Vogons to destroy the supercomputer, with the apparent excuse of building a hyperspace bypass. The Vogons destroyed the Earth five minutes before the Question was due to be announced, thereby destroyed ten million years of work.
Earth appeared in:
- The Douglas Adams book The Hitchhiker's Guide to the Galaxy.
- The first and sixth episodes of the television series.
- The novel So Long, and Thanks for All the Fish.
- The novel Mostly Harmless.
- The Eoin Colfer novel And Another Thing...
- The Primary, Quandary, Quintessential and Hexagonal Phases.
- The 2005 film
- The computer game.