Great question! By basics of prehistory, I assume you mean a theory that the earth is several billions of years old. By cosmology, I assume that you are referring to the concept of light years. Both of those two concepts are theories that have a lot of evidence supporting them but cannot be proved scientifically, i.e. using the scientific method, because they relate to the past. Since all those folks had was the Bible as their source, and paleontology was Greek to them, maybe you might start by asking them why there are accounts of dinosaurs (or dragons, which they were called before 1842) living in the Bible as well as, if some of them were learned, why there are accounts of such creatures elsewhere in history. You might also ask them why they believe while there is obviously evolution within a species or kind (cocker spaniel plus poodle equals cockapoo) that all the various kinds were created by a Creator and absent any complete fossil record of transitional forms they think that sometime in the future such fossils will be found which would support an alternative theory of creation. Their answers would help you formulate a response to them.