Continents are ancient puzzle pieces. It's easy to mentally reassemble the prehistoric supercontinent Pangea when we note how snugly South America fits along Africa's shore. But scientists have long debated exactly how this process unfolds, over hundreds of millions of years. The answer will allow them to predict what future supercontinents may look like.
Ross Mitchell, a geologist at Yale University, and his colleagues have recently proposed an new model of how supercontinents form. By measuring the ancient magnetism of geological samples, researchers speculate that the next supercontinent, which geologists call 'Amasia', will not form on the equator, but around the North Pole.
Traditionally, there have been two competing theories on how supercontinents form. The first, known as extroversion, states that Pangea fissured into continents (like North America), separated, and will someday form a new supercontinent – Amasia – on the other side of the world. The other model, called introversion, predicts that the continents will slow their drift and then collapse back together around the same area that Pangea originally formed.
Mitchell and his colleagues collected an array of geological samples and measured their magnetic orientation, essentially how the rocks aligned themselves with the magnetic poles of the Earth. Minerals lose their ability to magnetically align at specific temperatures, called the Curie temperature. For most minerals this temperature is scorchingly high. The Curie temperature of iron is around 1,400 degrees Fahrenheit. But many rocks are born in these extreme temperatures, and as they drop below their Curie Temperature their magnetic alignments become locked in place.
The Yale team sampled rocks of different ages, and saw how these frozen alignments changed over billions of years. Since all the rocks would have been oriented toward the Earth's poles, they could attribute any change in alignment to the motion of the continents. They then used this information to construct a new model of how supercontinents formed.
The new theory – called orthoversion – states that the continents will drift towards the North Pole instead of toward the equator or back to their starting points. The position of Amasia will be angled at 90 degrees from where Pangea once was. The geologists also found that the model helps explain how supercontinents that preceded Pangea had formed.
Peter Cawood, a geologist at St. Andrews University, commended the new theory in a recent February article of Nature, saying that, before orthoversion, geologists "...weren't quite sure whether there was method in the madness as you went from one [supercontinent] to the other."