This is sure to be an unpopular opinion, but I think alien life isn't as likely as we assume.

If you take everything we know about biology, biochemistry, and astronomy and calculate out the likelihood of having a large number of factors present in the same place to allow for life to begin in the first place Earth is very unlikely. I base this on biology and astronomy taught to me by somebody far smarter than I am.

First of all while silicon based life is theoretically possible it isn't likely there is a place in the universe where it is concentrated in enough abundance to be likely, and any speculation about it existing is only that. Carbon is far more abundant universally so we work from there. You need a planet the right size, with a moon for tides, the right orbit elliptically, distance from the sun, slant for seasons, composition, a nice gas giant like Jupiter to intercept any life destroying meteorites, a single star planet, more likely a spiral type galaxy, and a number of other factors that I have forgotten in the time between the initial learning of all these factors.

You have all these conditions and at the same time you need them in place for primordial goo to turn for a few hundred million years without utter planetary destruction to get dna to code for a ribosome, as well as the protein itself to come together randomly inside of a phospho-lipid bilayer which itself is a cellular level chicken and the egg occurrence.

That isn't to say there aren't an entire host of other possibilities for life existing involving science we don't understand fully, and I am probably butchering what somebody could explain who has a more active study in the related sciences could expand on.