The fact that few scientists are willing to devote their time and resources to a search for giant ground sloths is simply a reflection of the high-risk nature of the search that is, if they spend their grant money on a search for the giant ground sloth and fail to find it, then they will have wasted resources that could have gone to answering other important scientific questions. To me, this sounds like the marketplace of ideas in action. If he fails, then only a limited amount of scarce scientific capital will have been lost. I agree that Earth is not a living being in the same way that a biological species is, but this planet has attributes that would classify it as a life-form. The Earth is one of three planets that are exceptionally close in composition, size, and orbital stability.
Earth sustains life because it is the fittest planet, biologically speaking.
I say that these three planets demonstrate that natural selection can be applied to planets. Kind of reminds you of Goldilocks and the Three Bears. During a survival class, I demonstrated some of the different insects and grubs that can be eaten for sustenance. As I was having difficulty finding suitable beetle larva, I swallowed a live sow bug to prove the point. Much to my dismay, I found that they can live in the esophagus for a very long time and will repeatedly attempt to climb back up.