The Genesis Device was a sophisticated technological innovation designed to alleviate sociological problems such as overpopulation and limited food supplies. Its development was completed by a team of scientists led by Carol Marcus and her son, David Marcus, in 2285 on the Spacelab Regula I in the Mutara sector.
The device initiated a process of rapid terraforming, by which previously uninhabitable planets could be turned into class M worlds ready for colonization. This was accomplished by launching the Genesis Device, a torpedo-shaped projectile, into a lifeless planet. Upon impact, the device caused a massive explosion, reducing the entire area to subatomic particles. A preprogrammed matrix then reassembled these subatomic particles into the desired configuration, creating an atmosphere and environment habitable for Humans within a matter of hours, regardless of the test area's original composition.
Development and testing of the Genesis Device took place during a year-long period on a space station orbiting Regula, a class D planetoid. Tests were carried out by Dr. Carol Marcus and her team in three stages, the first of which involved experiments conducted in a laboratory on the space station. In the second stage, the device was deployed within a lifeless underground cavern deep inside the Regula planetoid. The intention of the third stage of testing was to introduce the device to a lifeless space body, such as a moon or barren planet.
Unfortunately, if the device was detonated where life already existed, it could prove to be a very powerful doomsday weapon, destroying all life in favor of its new matrix. Although speculated by David Marcus, this possibility seemed to catch its creators off guard, and they were unprepared for the consequences when Khan Noonien Singh stole the device and detonated it aboard the USS Reliant in the middle of the Mutara Nebula. The resulting cataclysmic explosion reorganized the matter that constituted the nebula (and possibly the ship itself) and formed a new planet, Genesis. The ship USS Enterprise was almost destroyed by the shock wave that resulted from the explosion before Spock sacrificed himself to repair its power system and the ship went to high warp just before the Reliant exploded.
Within an extremely short time, fully developed plant life emerged, but this seemingly tranquil planet had a highly unstable core caused by David Marcus' inclusion of protomatter in its Genesis matrix; this resulted in its aging rapidly. The planet suffered from wind storms, fires, and earthquakes that became more and more violent, until it literally tore itself apart in an explosion almost as tremendous as the one that had created it, destroying the life that had so recently been spawned. Hence, the Genesis Device turned out to be a grand experiment which, due to the use of protomatter in its matrix, ultimately failed. (Star Trek III: The Search for Spock)
The only mention of the Genesis Device and Project after Star Trek IV: The Voyage Home is in VOY: "The Omega Directive", in which Kathryn Janeway mentions "Marcus and her Genesis Device" as a comparison to other technologies deemed dangerously powerful.
There is some confusion as to whether the Genesis Planet is the nebula condensed into a planet, the shock wave hitting the Regula planetoid, or even the hull of the USS Reliant (or some combination thereof). It is also unclear which star the Genesis Planet orbited (the Mutara Nebula may have contained protostars, but none were observed although one pulsar is briefly visible in one scene behind Reliant). In addition, the status of the underground Genesis experiment (inside the Regula planetoid) is unclear. The novelizations of Star Trek II and III indicated that the Genesis wave absorbed Reliant, along with all of the gas and dust of the Mutara Nebula, which was used as raw material to create the Genesis planet. They also state the Genesis Device was programmed to make use of as much matter as was available, even creating entire star systems if there was sufficient mass. It is therefore surmised that the Mutara Nebula contained enough matter to create one primary-sequence star and one habitable planet.
According to Robert Hewitt Wolfe, Gideon Seyetik's terraforming technology in DS9: "Second Sight" was based upon the Genesis Device; "It was established Federation terraforming technology. Of course, the Genesis device didn't work, but obviously Seyetik's work is built upon the research of previous scientists. And it was a nice way to reference the movie." (Star Trek: Deep Space Nine Companion)
In the Myriad Universes story The Chimes at Midnight, in an alternate timeline wherein both Kirk and Spock are dead, the Whale Probe (as seen in Star Trek IV: The Voyage Home) decimates Earth, leading Carol Marcus to attempt to use the Genesis Device to fix its biosphere.
In The Genesis Wave series, Carol Marcus, alive but kept in a secret location due to her valuable knowledge, is abducted by a race of mysterious moss-based creatures that generate elaborate illusions to convince her to build a new version of Genesis. This version generates the Genesis Wave, a powerful wave of energy that traverses a significant portion of the Alpha Quadrant, terraforming all planets in its path to transform them into worlds suitable for the moss creatures to inhabit, as well as creating new waves of the creatures. During this series, it is revealed that most information about the Genesis Device has been highly classified, to the point that Captain Jean-Luc Picard has only heard rumors and vague details about the project before this crisis. However, the files regarding Genesis speculate that the problem with the Genesis Planet was that it was created from the excess mass of the nebula, and that the Genesis effect would have been perfectly stable if it had been used on an actual planet, as it was intended.