Life is not a class of physical processes as defined by science. Sure, it’s useful to define life in such terms for the purposes of biology, or even necrology, but the term and concept of “life” came about way before science was invented. Given a variety of possible ways to physically define life, how would we know which one or ones are valid? We’d select based on what’s obviously, intuitively alive or not, which is essentially what we’ve done. So, life as something intangible and not strictly defined takes precedence over life as something physically defined. Yet for some people the scientific definition of life is somehow taken to supersede the natural one.
Yes, the physical makeup of something is a function of, or correlates with, whether it’s alive or not. If a rock could transmogrify into a cellular organism, it might become alive; if a person turned into a rock, he would apparently have passed on. This merely shows that physical-life patterns/processes correlate with the presence of life qua life. Or more specifically, that the recognition of the presence of life correlates with specific material patterns/processes. It makes sense that we would recognize life only in its expression through certain kinds of material mechanisms, given that the senses we are using to recognize it are our sensate organs—senses of the material. Furthermore, it so happens that those material mechanisms we are willing to call “life” are those that significantly parallel ours—things with DNA, cells, an energy cycle, etc. Plants are alive, we say, but not as alive as organisms that have brains. So, apparently, the further away from being what we are something is, the less alive it is considered to be.
But who knows, maybe a rock is actually a very passive, peaceful type of being? At the very least, though, it could be assumed that, in order for life to have a physical experience, it must express itself through a suitably complex, dynamical and self-sustaining physical mechanism. In other words, bodies and plants could merely be vessels for actual life—hence the aforementioned correlations. In my view, life is a fundamentally magical, non-mechanistic, ineffable, cosmic, and ubiquitous phenomenon—if we could even classify it as a phenomenon.
What the fundamental characteristics are of the physical processes needed to constitute/catalyze life (or, in my view, merely make it apparent) is an interesting subject. A book called The Tree of Knowledge: The Biological Roots of Human Understanding, by Humberto R. Maturana and Francisco J. Varela, has some sophisticated and interesting things to say about that.