What do you mean by "alive"? Are you talking about biology or consciousness, or do you think the terms are intertwined?
Biology is incomplete when it describes "alive" - it has not reach universal consent on the matter,
If we take the modified "sesame" street and flesh it out a bit more -
Some process of movement, of nutrification and respiration (of utilising the gibbs free energy of the surrounding matter) and excretion (of converting it into matter of lower entropy) and multiplication of hydrocarbon based entities.
Then, consider the polymerisation reaction of ethane and methane -
Initiation
CH3CH3 ---UV/Sunlight---> CH3CH2* + H* (1)
CH4 ---UV/Sunlight---> CH3* + H*
Propagation
CH3CH2* + CH3CH3 ---> CH3CH2CH2CH2* + H*
Termination
CH3CH2* + CH3CH2* ---> CH3CH2CH2CH3
Multiplication
CH3CH2CH2CH3 ------------> CH3CH2* + CH3CH2*
Then it must be considered alive, given that here is a entity that can grow, absorb energy from it surroundings or nutrifies itself with reactants, it can multiply and excrete (2H*-->H2).
Of course, there has been some advancement since then and we have other criterion to consider, homeostatis and evolution - but then it leads back to earth question - since this planet is in a constant state of homeostatis and evolution, consequently the biological fraternity decides to pick and choose whether something is alive or not, than really defining it.
So, that takes it back to the physical, philosophical/Psychical sciences to justify it - and then we enter the realm of consciousness.
The problem that I have with people who try to explain consciousness as solely an attribute of humanity -is that it leads to idealism, wherein everything is seen as existing only in the consciousness of a macroscopic organism. The problem with this is it cannot account for the body in which that consciousness is instantiated. The whole must be broken into parts to have a theory of nature at all.
I think it is clear that the only thing in internal existence, is pure absolute consciousness, aware only of itself. All of us, as individuals, are sparks of that universal consciousness, but moreover, every actual entity (rocks, matter anything!!) including infinitesimal moments of present time are sparks of that eternal verity as well. This is how you divide the eternal whole into temporal parts. The details of how you do it will be the content of the next major breakthrough in physics, dwarfing the discoveries of Heisenberg and Einstein combined.