How did eastern North America form?

When Maureen Long talks to the public about her work, she likes to ask her audience to close their eyes and think of a landscape with incredible geology. She hears a lot of the same suggestions: Iceland, the Grand Canyon, the Himalayas. “Nobody ever says Connecticut,” says Long, a geologist at Yale University in New Haven in that state.

And yet Connecticut—along with much of the rest of eastern North America—holds important clues about Earth’s history. This region, which geologists call the eastern North American margin...