For decades, geologists have understood the broad picture of how eastern North America came to be. It begins with plate tectonics, the process in which pieces of Earth’s crust shuffle around over time, driven by churning motions in the underlying mantle. Plate tectonics created and then broke apart an ancient supercontinent known as Rodinia. By around 550 million years ago, a fragment of Rodinia had shuffled south of the equator, where it lay quietly for tens of millions of years. That fragment is the heart of what we know today as eastern North America.
Then, around 500 million years ago, tectonic forces started bringing fragments of other landmasses toward
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