You may be surprised to learn that portions of the North American continent didn’t actually originate on the North American continent. In fact, North America as we know it was formed as different landmasses, which were initially located far away across ancient oceans, collided with North America.
Professor Mike Dorais, a BYU geology professor who regularly researches the Appalachian Mountains in parts of New England, tells us that rocks are a history book of sorts:
“Sometimes we have to look on a very small scale in order to see the big picture,” he said. “The composition of a rock can tell us a lot about how Earth formed.”
Through his analysis of rocks in New England, Professor Dorais has found that some North American rocks match the composition and characteristics of rocks found in South America and even Africa.
According to Professor Dorais, subduction is to blame. Occurring at a rate that is too slow to be seen by human eyes is a battle that happens between our planet’s tectonic plates. This battle, called subduction, happens when one plate slides under another. The plate on the bottom is recycled into the Earth’s mantle by this subduction process.
Over millions of years, “the oceanic plates have moved and been consumed in subduction zones. This causes the ocean basins to get smaller and smaller over time,” Professor Dorais said. “Oceanic islands, microcontinents, and even other continents that are attached to these oceanic plates move as well. They are carried by the oceanic plate “conveyor belt” until they arrive at a subduction zone and collide with each other. When continents collide, it’s a car wreck!”
The eastern side of the North American continent has been victim to this sort of tectonic attack several times. “Just since about 470 million years ago, practically yesterday in terms of Earth’s history, there have been about four, if not five, collision events in the Northern Appalachians,” said Professor Dorais.
This kind of collision, called an orogeny, is one of the ways that mountains are created. When the Atlantic Ocean began to open around 200 million years ago, portions of crust that collided with North America were left behind.
“Some parts of New England weren’t originally part of North America at all, but rather are fragments left behind from the ancient supercontinent of Gondwana,” said Professor Dorais. This supercontinent included almost all of the current continents on Earth. Dr. Dorais added that during the formation of Gondwana things got, “…plastered on, and when everything split apart again, they remained attached to North America.”
America hasn’t always been a victor in these tectonic wars, however. Sometimes we lose a piece: “Scotland comes from North America,” remarked Professor Dorais.