After reading about Alvarez and the limestone, you should be able to say that the passage was about more than just Alvarez looking at limestone. The point is to talk about how a theory was challenged. Which theory? The theory of incompleteness – the Alvarezes believe that the evidence wasn’t lacking for animals during the Cretaceous period. The animals went extinct because of a meteorite.
Were you to paraphrase the passage (remember, as though you were talking to an intelligent 12-year old) your paraphrase should not be, “uh, it’s about this guy and he like finds this rock, and uh…” (you are not paraphrasing to Beavis and Butthead). Instead this would probably suffice:
This scientist found a layer of rock in which it was indicated that much life on Earth had suddenly vanished. He’d learned that any hole in the fossil record meant scientists simply had yet to find