Provided you're actively and systematically looking for evidence, then absence of evidence is evidence of absence.
We've just now learned how to analyze atmospheres of exoplants.
5 years ago, we couldn't see exoplanets smaller than jupiter.
A decade ago, we couldn't see exoplanets at all.
I find the entire idea that life could only exist on earth farcical. A lot of people in this thread don’t seem to understand that we can’t directly image many exoplanets to begin with and that we haven’t even been trying to find life on other planets and moons in our own solar system, it has in fact been suppressed every time credible circumstantial evidence of life is found (Viking lander experiments and methane on mars both come to mind)