As i remember it, at the end of Firestorm... that was the point of the storyline. The idea was to search the tacitus for ways to solve the tiberium riddle... begin reversing the effects of tiberium spreading over Earth (ref: veinholes, tib floaters etc)
I suppose if anything, thats the main question... how did we go from a TS universe where such life existed to the TW scene where such life isnt around (least i havent seen any)