[bluGill]

We don't really know what life requires. We know that earth has life. We have insufficient evidence for anyplace else (there is some evidence of life in our solar system but it could have been life that escaped our orbit by chance, or just contaminated sensors). All we have for sure is life exists on earth, so we know life exists on earth.

Wikipedia has a list of other chemistries that could maybe support life, but we don't know if they do in the universe or not. We know that the basics of life on earth (water, carbon) are very common in the universe, and so there is no reason to think that life as we know it should be rare - but we also have no evidence of life elsewhere (mostly because we don't even have the ability to see evidence if it exists - the universe is large and we can't detect the important things even a few light years away)

[mcmoor]

And also that all our sister planets isn't like earth, and they all don't have life (as far as we observed). So it's another point for "not like earth"->"not have planet". Before those expeditions, we thought that fucking sun also has life on it https://adsabs.harvard.edu/full/2011JAHH...14..169C