the Genesis device was developed to reformat a planet into a earth clone pure and simple. It would if deployed on a planet with life, Kill all of that life. Rip it to base atoms and then use it to create this earth clone with plant life and limited microbial life.
That's what Spock meant when he and doctor McCoy were in a debate.
McCoy:"My god... To think that we... Suppose this thing were used on a planet where life already existed?"
Spock:" It would destroy such life in favor of it's new matrix."
McCoy"Its new matrix? My god man have you any idea what your saying?"
Spock: "I was not attempting to debate its ethical implications, as a matter of cosmic history, its always been easier to destroy then to create."
McCoy: " Not any more! Now we can do both at the same time! According to Myth the Earth was created in six days, now Watch Out here comes Genesis! We'll do it for you in Six Minutes."
Spock:" really doctor you must learn to govern your passions. Logic suggests..."
McCoy:" My god the Man's talking about Logic, we're talk'en about Universal Armageddon! You green blooded Inhuman..."
(No I did not look that up or re watch the movie I pulled that from my own memory)
its likely that the mechanism at work in Genisis may have involved nanites as that is the only way I can think of to do what it did in such a manner.
imagine for a moment that we have the classic fan battle star wars vs trek with the reliant under Khan attacking the deathstar. Reliant makes a run and fires Genisis at the deathstar. So what happens? Well in our thought experiment the deathstar now undergoes a massive set of changes. The entire structure is ripped apart including droids and storm troops. The grey mass effect is taking place as nanotechnology goes to work using the existing matter to reproduce its self. The mass of the death star is increased as a artificial gravity well draws in more material increasing the mass to earth equivalent
the nanittes at the core of the structure now change into a mass of iron, nickle, a mantel of molten rock and radioactive elements, and the outer structure becomes a rockie crust. Now begins the next step. The forming mantle now expels a mix of gasses, hydrogen, oxygen, methane, carbon dioxide, argon, nitrogen, Ammonia, these gasses form a crude atmosphere. In this environment a simple form of preprogrammed long chain polymer is creates as single celled organism are created with a existing genetically engendered DNA sequence forming a advanced now organic slime like allege.
Hydrogen and oxygen are forced to fuse forming chains of one hydrogen to two oxygen, oceans of sweet water form. Other material is filtered and carbon is used to fuel the rapid development of genetically engineered plant life. Flora only. Fauna is not allowed at this point as any president would undergo massive changes and become either mutated or in the case of dead tissue resurrected. The flora follows preset molds, trees, flowers, grasses, ferns and the like. The nanittes now change forming micro organisms that help sustain the environment until fauna is added.
so what went wrong? Why is it that Genesis is not seen post star trek 3? Its unstable. The trek answer is something called "protomater" which is considered dangerous and unpredictable. The planet produced is going to continue having massive geological shifts and changes as it burns its self and breaks down the planets core is adding mass to itself increasing its heat and radioactivity until it reaches the point where its own mass sets it off like a huge atomic bomb.
The genesis device was a analogy for the use of radiation and atomic energy particularly nuclear weapons that seen in the early period of the twentieth century. Along side the bomb was seen a plethora of supposed new technologies that would have made life a virtual paradise until radiation's harmful effects were realized.
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