Why clone extint Animals and plants if Earth is dead as Jake claimed?

[PunkMaister]

I know most here go with what Jake said plus what little has surfaced online of the guide and the few pics of a nameless city of Avatar Earth to reach the conclusion as I once did that Earth is a lifeless rock. But as it turns out both the script and the guide speak of animals that had become extinct and had been brought back through cloning or where in the process off. So it is clear that they were cloning animals and plants that become extinct, the question is why bother if Earth according to Jake (if we are to take his words literally) is nothing but a lifeless rock?