What is life? You would think that a biologist would be able to tell you the answer. After all, that’s their field of study. But there really is no great definition. There are a few different characteristics that life seems to have: the ability to grow, the ability to reproduce, the ability to maintain a constant internal environment (homeostatis). This is more or less scrap for my thoughts on the matter of life. But here is one thing that life seems to always do: it seems to evolve. I would argue that evolution is crucial to any definition of life.
Life is any enclosed system which includes an ACTIVE mechanism which drives the evolution of that system.
I think that would make the biosphere “life” but I’m okay with that. But the definition just does not seem robust enough.
A living system is a member of a class of enclosed systems, which possess an active mechanism by which they can induce evolution in new elements of that class.
This would more or less cover all known forms of life, which unfortunately are all forms of life which arise from a common origin, but it seems like a good starting point. It would also exclude fire and viruses. Fire doesn’t really evolve. Viruses evolve, but the process of inducing evolution in new members of the class is entirely passive.
Possessing an active mechanism to induce evolution in new members of the class would also most likely imply metabolism and reproduction. Homeostasis may not be directly implied by the definition, but it’s difficult to say. The other results may require or result in the ability to maintain homeostasis.