Scientology has an, er, unusual basis according to Hubbard's writings.
http://en.wikipedia.org/wiki/Xenu
The story of Xenu is covered in OT III, part of Scientology's secret "Advanced Technology" doctrines taught only to advanced members who have undergone many hours of auditing and reached the state of Clear followed by Operating Thetan levels 1 and 2.[7][12] It is described in more detail in the accompanying confidential "Assists" lecture of October 3, 1968, and is dramatized in Revolt in the Stars (a screenplay written by L. Ron Hubbard in 1977).[7][22]
Hubbard wrote that Xenu was the ruler of a Galactic Confederacy 75 million years ago, which consisted of 26 stars and 76 planets including Earth, which was then known as "Teegeeack".[5][8][23] The planets were overpopulated, containing an average population of 178 billion.[1][4][6] The Galactic Confederacy's civilization was comparable to our own, with aliens "walking around in clothes which looked very remarkably like the clothes they wear this very minute" and using cars, trains and boats looking exactly the same as those "circa 1950, 1960" on Earth.[24]
Xenu was about to be deposed from power, so he devised a plot to eliminate the excess population from his dominions. With the assistance of psychiatrists, he gathered billions[4][5] of his citizens under the pretense of income tax inspections, then paralyzed them and froze them in a mixture of alcohol and glycol to capture their souls. The kidnapped populace was loaded into spacecraft for transport to the site of extermination, the planet of Teegeeack (Earth).[5] The appearance of these spacecraft would later be subconsciously expressed in the design of the Douglas DC-8, the only difference being that "the DC8 had fans, propellers on it and the space plane didn't".[21] When they had reached Teegeeack, the paralyzed citizens were unloaded around the bases of volcanoes across the planet.[5][8] Hydrogen bombs were then lowered into the volcanoes and detonated simultaneously,[8] killing all but a few aliens. Hubbard described the scene in his film script, Revolt in the Stars:
Simultaneously, the planted charges erupted. Atomic blasts ballooned from the craters of Loa, Vesuvius, Shasta, Washington, Fujiyama, Etna, and many, many others. Arching higher and higher, up and outwards, towering clouds mushroomed, shot through with flashes of flame, waste and fission. Great winds raced tumultuously across the face of Earth, spreading tales of destruction ...
—L. Ron Hubbard, Revolt in the Stars[7]
As an atheist I don't believe in any god or gods (don't take this as an attack, theists!) but I do believe there's a very good chance that there are other civilizations out there. But Hubbard's description of them is way off the reservation.