[Eric A. Taylor (OP)]

I read that if you took yourself apart one atom at a time you'd end up with a pile of fine powder none of which had ever been alive but all of which had once been you. At the atomic and molecular level nothing can be said to be alive. What exactly does it mean to be alive? What chemical changes happen when a living thing dies? How long, after clinical death, does it take all the cells in your body (your own cells, not the bacteria that live on and in you, which are not part of you) to cease living?

  There are several cases in which people have been dead, even held under water for 30 minutes or more, then revived. Today doctors routinely kill their patient to perform surgery then revive them. What's happening here?

[RD]

Since there is no unequivocal definition of life, the current understanding is descriptive,
 where life is a 'characteristic' of organisms that exhibit all or most of the following phenomena ... Homeostasis...Organization...Metabolism...Growth...Adaptation...Response to stimuli...Reproduction

http://en.wikipedia.org/wiki/Life#Biology