Tiberium is Strange Matter
In the Intel Database it is declared that Tiberium can transform any matter it comes into contact with into more of itself. The process is actually quite plausibly explained even though there's no mention of any Strangelets. Basically the Tiberium being incredibly radioactive bombards all surrounding matter with heavy particles which break up the cores of said matter. Some of the released protons are then caught by Tiberium's attractive forces and incorporated into it.Tiberium did not really evolve, its true form was always the same.
Even though it's stated that "first forms of tiberium were almost organic in nature" it always manifested itself as green (and later also blue) crystals. The fact that they sprouted from organic fungi-like pods does not necessarily mean the substance itself is organic in nature. It just mutated terran lifeforms to help it spread. By the time of the Third Tiberium War the Tiberium's most common form is a self-replicating proton lattice (which sounds pretty mundane baring the self-replication part) - the very same Green Rocks seen throughout the entire Tiberian Series. The reason it required organic life in the early stages is because its concentration was too low to affect heavier matter. Once the Tiberium's concentration became sufficiently dense, its forces were strong enough to affect even the heaviest elements and the drastic increase in radioactivity became too much even for the mutated lifeforms to handle, explaining why they gradually disappeared. In the end Tiberium itself didn't really change its nature. It just grew in mass.The bad ending for the GDI campaign leads to Tiberian Twilight.
The final GDI mission, set at Ground Zero in Italy, has the commander choose whether to use a Liquid Tiberium Bomb secretly prepared on Director Boyle's orders (finishing the fight immediately) or heed General Granger (ending the war while sticking to GDI's convictions). Given how destructive the Liquid Tiberium detonation under Temple Prime had been, and Granger's warnings mention how deploying such a bomb right where Tiberium first arrived on Earth could have unforeseen consequences, it's not hard to see Boyle's short-term victory lap resulting in the material expanding uncontrollably, and far beyond GDI's ability to counter it. Which, in turn, leads to the decrepit situation seen in at the start of Tiberian Twilight.- This may also add more to why Kane specifically had LEGION spare Boyle in the first place. He knew that the man would not only be reckless and foolish enough to attempt a Liquid Tiberium Bomb strike, but that his vainglorious escapades would eventually leave GDI near-terminally crippled and desperate enough that the Messiah could offer his solution with almost no questions asked.
