Mississippi appeared to run backwards. The quakes woke New Yorkers, rang church bells in Charleston, South Carolina, buzzed bemused Torontonians a country away, and brought down chimneys from St. Louis to Cincinnati. Because the deep rock in the middle of the continent is older and colder than out west, strong shaking was felt over an area 10 times that of the 1906 San Francisco earthquake. An alarmed President James Madison even wrote Thomas Jefferson from DC about the tremors. The shocks occurred on what today is the least understood seismic zone in the United States. And depending who you ask, another major earthquake here represents either a towering threat for which the Central U.S. is woefully unprepared, or a wildly overhyped phantom costing taxpayers hundreds of millions ofdollars in needless infrastructure improvements.

* * * Not far from Memphis and St. Louis, 600 million years ago, the continent tried to rip in half. It failed. But even calling this “the continent” is misleading: North America was probably south of the equator, almost upside down, and had just fractured out of a larger supercontinent called Rodinia. East Antarctica was to the northwest, eastern New England and the Canadian Maritimes were perhaps on a different part of the planet, stitched onto Africa, and a piece that was about to break off of “North America” would eventually end up in the middle of Argentina. This was not our world. This world was still convalescing from the near-death experience of Snowball Earth—having hurtled in and out of planet-wide glaciations, and