Geologists have used the remains of ancient subduction zones beneath North America to radically rewrite the history of the continent.

The new image of an earlier North America includes a more fragmented west coast and a sprawling archipelago in the Panthalassa Ocean, which was previously depicted as empty.

"Now it fits together," said Karin Sigloch, seismologist at Ludwig-Maximilians-University in Munich. "We've come up with a pretty different solution that I think will hold up."

Two hundred million years ago, North America was part of the supercontinent Pangaea, which was surrounded by the vast Panthalassa Ocean. Once North America started shifting away from Pangaea, geologists believed there existed a subduction zone along the west coast that absorbed Panthalassa's oceanic tectonic plate, the Farallon plate. The North American terrain derived from the subduction zone.

Sigloch and colleague Mitch Mihalynuk, however, were skeptical and, by examining remnants of oceanic crust beneath North America, they found a massive wall of oceanic crust segments stretching from Canada to Central America. The slabs mark the location of Panthalassa's subduction zones.

"What this does is provide us with a time machine," Mihalynuk said. "The slabs are telling us the sites of past ocean trenches and the locality of island arcs, which are the building blocks of continents."

The evidence shows that a large archipelago sat off the coast of North America. It was 6,200 miles long and shaped like an arrowhead. It also revealed a subduction zone that dipped to the west rather than the east.

"The ocean basin was not a vast abyssal plain," Mihalynuk told OurAmazingPlanet. "The situation is much more like the Southwest Pacific than offshore South America."

According to Mihalynuk, the discovery is significant in overruling decades of accepted knowledge about the formation of North America.

"It will take a while for people to turn around. That intellectual ship has a lot of inertia," he said. "This is one of those eureka moments."