In the early 1800s, a young man named John Cleves Symmes Jr. (so named to distinguish him from his prominent eponymously-named uncle) charmed American audiences with his "Hollow Earth" lectures. He claimed that a giant hole in Siberia was the entrance to a whole new world that could be colonized and made just as prosperous as the one our ancestors lived in. His "Concentric Spheres" theory was very popular, and Congress actually appropriated funds for an expedition to find the hole and claim the new lands for the United States.His uncle's wife was the sister of President Harrison, so he had some inside influence. As far as I know, he never actually went to Siberia. Nevertheless, there's a monument to Symmes in Cincinnati or Cleveland.
This theory was widely accepted, and bred a variety of tales. Jules Verne wrote one of the first, "Journey to the Center of the Earth."
This new hole in Siberia will almost certainly spark a quiet revival of the Hollow Earth Theory. Yes, it's nutty, but I see little difference between Symmes' theory and Keynes'.