The dividing line between lifelessness and life, what exactly is it? There is no dividing line.
In other words, how does inanimate matter suddenly (and literally) come to life? Ingestion and digestion, but it doesn't happen suddenly.
Or does the naturalist/atheist posit that what we call life, biology, in plants and animals is different from the activity of molecules or subatomic particles only in degree, not in kind? It does not differ at all.
A: Life
Circular argument.
Q: The dividing line between lifelessness and life, what exactly is it?
A: There is no dividing line.
This would appear to contradict your first answer above.
Q: In other words, how does inanimate matter suddenly (and literally) come to life?
A: Ingestion and digestion, but it doesn't happen suddenly.
We have machines that ingest and digest on one level or another. Have they come to life? And besides, of course it happens suddenly -- you have a thing that is either ingesting/digesting or it isn't. There is an infinitessimal point in time between the last moment when said thing isn't ingesting or digesting and the first moment when it is. There's no in between or limbo period for this any more than there is such a thing as being partially pregnant.
Q: Or does the naturalist/atheist posit that what we call life, biology, in plants and animals is different from the activity of molecules or subatomic particles only in degree, not in kind?
A: It does not differ at all.
As I said in my original post, I anticipated this answer. But to believe this is so has consequences for humanity that are disastrous, e.g., that no living thing has any more inherent value than any piece of inanimate matter. As Dennis Prager put it: "Only if there is a God who created man is man worth anything beyond the chemicals of which he is composed." Throwing a soda can or a baby out of a moving car must therefore be either two equally moral, equally immoral, or (for any disaffected college students or other budding nihilists present) equally amoral acts; but it is not possible under such a belief system to say that one is any more or less moral than the other.
No, this is not a thread on philosophy or religion or morality per se, but my point with the previous post and this one are to show that at the end of the day, all are inextricably linked...