P.Z. Meyers says creationism isn't as old as we assume:
The mainstreaming of literalist creationism occurred in the 1960s, when John Whitcomb and Henry Morris wrote The Genesis Flood. It's basically the same nonsense he Seventh Day Adventists were peddling, but Whitcomb and Morris were not SDAs, making it possible for conservative Christians, who regarded Seventh Day Adventism as a freaky cult, to coalesce in the formation of the Creation Research Society. These people had no ambition to convert the research community, but instead wanted to wean bible-believers away from what they considered the compromises of day-age and gap theory.