Bacterial life is already pretty simple, indeed, many organelles in eukaryote cells are bacteria-like structures and are probably descended from them. If life elsewhere in the universe arises like ours, bacterial life is most likely. Bacteria where the only form of life on Earth for nearly 3 billion years, while multicellular life has existed less than 600 million. Life arose very quickly on Earth, suggesting it is likely, or at least easily achievable under the right circumstances. Multicellular life, conversely, seems much less likely (though that may be more due to the time it takes for bacteria to prepare the atmosphere for more complex life).
But I could not honestly claim that alien life, simple as it may be, will be bacteria. I only have a sample size of 1 to work with.
But I do doubt the candidacy of Silicon as a basis for the molecular structures of any form of life. It is proposed as an alternative because, sitting directly beneath Carbon in the periodic table, it can form four covalent bonds just like Carbon, required to form the sort of complex structures Carbon can. However, as you may have noticed, Carbon produces a great many kinds of substances: Hydrocarbons, Carbohydrates (sugars), proteins, nucleic acids, lipids (fats and oils), tiny monomers and hugely long polymers. By itself, Carbon makes rocks. Conversely, silicon, in all its forms, makes rocks. And that's pretty much it. Glass also. Some of them, crafted in impossibly complex, tiny and delicate ways, are incredibly useful to us, but they are still rocks.
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