I was raised on the Torah, my wife on the Qu'Ran, my eldest son is an Atheist, my youngest is a scientologist, my daughter is studying Hinduism, I imagine there is room there for a holy war in my living room, but we practice live and let live.
Why it is hard sci-fi
A man tells a small group of his academic colleagues that he is a fourteen-thousand-year-old Cro-Magnon survivor. The entire film is the conversation that follows. The colleagues stress-test his story across biology, archaeology, history, religion, and physics. The film is rigorous about the kind of evidence that would and would not be available to confirm the claim, and treats the conversation as a peer review rather than a confession.
Science inside it
Negligible senescence, the historical record as a stress test for a single witness, isotope dating, and the limits of memory across deep time. The films interesting argument is that any sufficiently old human would have left no legible signature in the record, because the record is too thin and too biased.