As it happens, my senior thesis in college was largely about Young Earth Creationists and now that Marco Rubio’s got the idea back in the news I’m feeling fussy about it.
The key thing here is that contrary to what people often say, there’s absolutely no empirical evidence that the planet earth is 4.5 billion years old rather than 4 thousand years ago. Take the standard scientific account of what the earth was like in 2000 BCE. Now imagine that God create the universe exactly like that 4,000 years ago. He put fossiles in the ground whose state of carbon decay was just so. There’s no “evidence” about this hypothesis one way or the other. Scientific materialism just incorporates as a baseline assumption that these kind of radical discontinuities in the nature of reality don’t happen. But maybe they do?
Do they? Of course not. I think that’s ridiculous. Just like it would be ridiculous to say that roasting toddlers for dinner is morally acceptable. But we can’t empirically prove that toddler-roasting is wrong, any more than we can disprove the “God is playing an elaborate joke on us with the fossils to test our faith” account of geology.