Thanks very much, Stu. I think your “clear demarcations” are an illusory artifact of our use of language. You say “at one point nothing was alive, and then it was”, but that depends, of course, on how you define “alive”. Making the definition depend specifically on RNA or DNA molecules seems to me to be way too restrictive; it’s possible to imagine life on other planets being based on other chemistry. Defining life in terms of self-replication may be better, though is that a necessary condition, or is complex behavior enough? And if we take self-replication as a necessary condition, did self-replicating molecules arise suddenly from other molecules, or was it a gradual process? I have read that some kinds of molecules in clays can replicate under the right conditions, as structures replicate in crystals. So I don’t see the clear demarcation in time that you see for the origin of “life”.

Similarly for the universe, as Ethan Siegel has pointed out, there is a difference between the “big bang” and the origin of the universe. You wrote, “logic tells us that at one point in time there was not universe … and then there was …”. The fallacy in that lies in the phrase “at one point in time”, for that assumes our conception of time as a doubly-infinite line with points along it. But it’s possible that the universe, including the doubly-infinite time line has always existed, and that the point you are thinking of is the time of the big bang, not the whole thing itself. So in two ways science may be unable to account for the ultimate origin: (1) There may be no ultimate origin to account for, and (2) scientists may not be able to observe events before the big bang to develop any explanation of why it occurred.