Much of this this thread has been anthropocentric. That's not bad in itself, since self-preservation is not a bad thing, but let's get some perspective.
If an alien culture managed to show up here (even in the most benign way) they certainly would want to crawl over this blue ball with a fine-toothed comb. We have so many organisms, so many micro-environments, so many extreme environments (at least to our minds) that the Earth would be a treasure to them. We have deep ocean critters living on the emissions of volcanic vents at the bottom of the sea, we have arctic critters that can feast in good times and lay low in bad times and make it through season after season, and we have such a variety of life (of all kinds) living in the temperate, sub-tropical, and tropical zones, that it would take exobiologists millennia to make sense of it.
We could have micro-organisms in our soils, waters and air with characteristics and metabolic processes that could solve puzzles that they have been plaguing them for a long time. I think that the most reasonable response to expect from sentient aliens would be "do no harm, study, and do not disturb the natural order".