Specifically it was the development of geology as a science, as the context in which to place dinosaur fossils. Dinos by themselves were taken by many religiou

Specifically it was the development of geology as a science, as the context in which to place dinosaur fossils. Dinos by themselves were taken by many religious people to be the abominable creatures destroyed by the flood, which Noah was not able to save in his ark. Geology is what discredited the 6000-year-old-Earth idea. Even before radioisotope dating, it was clear that there was sedimentary landscapes that would’ve taken tens or hundreds of millions of years to form. And then there was fossils of megafauna right in the middle of these rocks? That, plus Darwin’s alternative explanation for the origin of life, is what broke the creationist narrative.