In The Hitchhiker's Guide to the Galaxy by Douglas Adams, an Earthman is affronted to find that his planet's entry in the Guide consists only of the single word "Harmless". The Guide researcher reassures him that the next edition will improve upon this. The new entry will read, "Mostly harmless." The Guide also tells of the creation of earth by inhabitants of the planet Magrathea, as a giant computer. It also mentions that we are descended from middle men. The Earth is located in sector ZZ9 Plural Z Alpha.
The Earth seems to play a huge part in the Star Trek universe, the Doctor Who universe, and others.
It is also common, in science fiction set far in the future for Earth to fall into one of four categories. First, its location could have lost to the sands of time and with the planet presumed destroyed or rendered uninhabitable or even no one (human or otherwise) caring where it is. This scenario is expressed in the Foundation series by Asimov, among others. Second, Earth's location could be unknown except for the few who live there, usually in some manner of utopia. Third, Earth could be a member of whatever interstellar community exists in the work, whether as a minor or major player. This is by far the most common option, and Earth (no doubt due to anthrocentrism) is usually a major power-broker. Fourth, Earth could have been completely destroyed or rendered uninhabitable, but its location (or at least its former location) is well-known. This last scenario is also popular, and was featured in the movie Titan A.E.
See also
Gaia, Gaia hypothesis, Earth (element), Midgard, Arda