I believe that primordial, simple life is a common thing in the universe and that a serious fraction of Earth-like planets may host microbial or even vegetal or animal lifeforms.
Hierarchy of “stuff” …
My feeling is that life is an inevitable way for « stuff » to evolve and gain complexity: The universe started with energy, then was a primordial soup of elementary particles, then first Hydrogen and Helium atoms formed. Then came chemistry and the formation of bigger and bigger molecules arriving to proteins and DNA, thus LIFE, most complex level of « stuff » organisation that we know.
Passing to the next level …
In terms of scale though, only a very small fraction of « stuff » passes to the next level of complexity: Only 4% of it had « evolved » to conventional barionic matter (the rest being Dark Energy or Dark matter). Matter itself is mostly small atoms: Hydrogen & Helium form 98% of matter in the Milky Way. Bigger elements are rarer as this « evolution » needs more specific conditions as the complexity grows. Carbon, fundamental element of all organic molecules represents only 0,5% of the total mass of the galaxy, for example.
Consciousness …
Chances are that this pattern still apply for more complex organisation levels, and the fraction of stuff that evolve is getting ridiculously small as the complexity grows. The most complex level that we humans can think of so far is intelligent life capable of consciousness. It is the ultimate level that finally gives a meaning to all this mighty dynamic : A universe without a consciousness that observes and comprehends it is at least meaningless.
Rarest thing ever …
All of this make me think that intelligent life, or « consciousness », meaning an entity capable of comprehending itself and its environment, the most complex « stuff » can get (?), is the rarest phenomenon in the universe, rarer than supernovae or quasars, thus have occurred only in some occasions in the universe during its 13,7 billion years of existence (maybe once so far !). A very common argument for this is that after all, Earth had developed intelligent life only once in 4,5 billion years of existence, even if the conditions suited well.
Unlikely meeting …
So what are the chances of meeting such a life form? Assuming that we coexist in the same « observable » universe, meaning we can reach each other within our respective civilization lifetime, conditions that led to this intelligent life (gravitational pull of the home planet, level of exposure to radiation, atmosphere composition, available energy sources …) would be potentially so different than ours that the outcome might be radically different than us: life forms the we can’t even imagine nor communicate with or even detect.
A supreme consciousness at reach …
And what if the intelligent life or « consciousness » we are looking for is closer than we might think? the same way individual « unintelligent » neurons come together and form a brain capable of consciousness, humanity as a whole, with the interaction of the individuals, especially in an information technology era, form a kind of supreme consciousness (collective intelligence) which is capable of more than we individual humans are such as predicting the future, reading the History record within our collective memory and comprehend transcendent concepts that still elude us such as time, infinity and nothingness.
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