I thought it was a National Geographic episode about fossils....
I still remember the show when Letterman admitted to having improper sexual relationships with staff.
It was a shocking admission, but, I remember the audience cheered and laughed at that. It made me think, wow, his audience has no morals, no sense of decency, that even what was supposed to be a serious solemn admission of wrongdoing is greeted by the audience as if it is comedy.
This is happening about fifteen years past his funny expiration date.