They've never thought about it. Creationists don't do science. They just attack it.
That's why it's so annoying. And not only that, but they quote-mine for anything, any article or report that seems to contradict evolution on some minor thing, and voilá, that means that all and everything of evolution must be false to them! Just because blahblahosaurus wasn't related to mehwhateverosaurus doesn't mean the whole thing crumbles down.
I know most of them don't believe sedimentary layering is a reliable measurement of time passing. Yep - they don't believe in grade 7 level geology. When it comes to different evolutionary eras appearing at different layers, they say it's because the heaviest animals stunk the fastest during the flood. Lol.
Or the other 50 methods of dating. Many of them radioactive, but some of them chemical, magnetic, and other methods of dating. Preferably, each dating of a site is done by at least 3 methods, sometimes more. They all confirm each other, not perfectly because of small errors (which is natural considering rounding errors and also problem of measuring exact), but they match up quite well. Earth is not 6,000 years old, that's guaranteed. It's much, much older. And like you're saying, geology, it's well established science. To deny evolution is to deny geology, astronomy, math, ecology, biology, chemistry, physics, sociology, anthropology, archeology, ... and so on. In other words, denying evolution is to deny reality.
That's something else I could set out to find - evidence of heavy animals sinking faster in a modern day flood, replicating the pattern we see in the fossil record.
Strange thing that the lighter dinosaurs sank as fast as the heavy dinosaurs, while the horses, elephants, and whales, or other heavier animals than the light dinos managed to swim above the turbulent waters and mud sucking them down. I think there must've been an intelligent drowner... (cheek-in-tongue of course)