The formation of supercontinents is a relatively unknown phenomenon, especially since humans have never observed it. But in understanding the processes of supercontinent formation, we may be able to predict future changes in Earth’s surface and mantle for millions of years to come, while also aiding in our understanding of Earth processes. Two theories predominate as to how supercontinents form: introversion and extroversion. Introversion postulates that a younger and interior body of water will close, forming a supercontinent in its place. Today this would be the closing of the Atlantic Ocean, about where Pangaea was located. Extroversion postulates that an older and exterior body of water will close, forming a supercontinent in its place. Today this would be the closing of the Pacific Ocean, opposite of where Pangaea was located. However, both of these theories have gapping holes in them, especially when compared to geological evidence of mantle movement, both in more recent times and on the million-year timescale. Mitchell et al. (2012) have proposed a new model, orthoversion. Orthoversion is the formation of supercontinent in the downwelling girdle of subduction (today the “ring of fire” in the Pacific) orthogonal (90°) to the predecessor supercontinent. Using seafloor spreading patterns and changes in paleomagnetic poles, the authors were able to recreate potential centers of former supercontinents Pangaea (~200 million years ago (Mya)), Rodinia (~600 Mya), and Nuna (~1000 Mya). Then using their orthoversion model, they were able to recreate the movement of continents from one supercontinent to the next. The significance of their model is that it clears up the gaps present in the other models. The orthoversion model provides the missing link in Pangaean formation, and is the only model that matches ocean records in showing that the Pacific Ocean rift has only existed since the creation of Pangaea. By creating and presenting the orthoversion model, Mitchell et al. have shown that orthoversion explains the connection between supercontinent decline and growth, and many other gaps in the other two. –Mathew Harreld
Mitchell, R.N., Kilian, T.M., Evans, D.A.D. 2012. Supercontinent cycles and the calculation of absolute palaeolongitude in deep time. Nature 482, 208–211.
It is now well-known that millions of years ago a “supercontinent,” named Pangaea, dominated Earth’s landscape. Since its formation about 200 million years ago (Mya), the continents, as we know them now, have been shifting. In the following millions of years the continents will continue to shift, once again forming a supercontinent, already named “Amasia”. Understanding the processes of how Amasia might form requires discovering how the supercontinents of the past have formed. Two general theories are prevalent in today’s scientific literature: introversion, extroversion. The introversion model is based on the idea that young interior oceans stop forming and then begin to close, creating a collision between two landmasses. In today’s terms this would mean the closing of the Atlantic Ocean, and the collision of the Americas, Europe, and Africa. This will mean Amasia will form where Pangaea once was. Extroversion is the process where the relatively older, exterior ocean closes, forming the supercontinent in its place as two landmasses collide. In today’s terms this would be the closing of the Pacific as Asia, Australia, and the Americas collide, forming Amasia opposite of where Pangaea formed. However, both of these theories have deep gaps in their explanations, especially when compared to geological evidence. Mitchell et al. have developed a new theory called orthoversion. Orthoversion is the prediction that a supercontinent will form orthogonal (90°) to its predecessor, in a region of downwelling, and in the subduction girdle formed by its predecessor. Today this would result in the closing of the Arctic Ocean, as North America and Northern Europe meet to form Amasia. Amasia would be formed in the Pacific region, based around the Pacific’s “ring of fire”, and eventually close the Atlantic Ocean and the Caribbean Sea. Each of the models shows that Amasia will be formed with Asia at its center.
To show that any one of these models is more accurate than the others in forecasting the future, the models must first recreate the past. Using their orthoversion model, Mitchel et al. are able to show that previous supercontinents have orthoverted from one to the next, all the way back to 1000 Mya. By creating a model based on geological records of landmass centers and supercontinent centers, the authors were able to recalculate their movement, based on of the orthoversion model. The landmass and supercontinent data are acquired from seafloor-spreading records that allow for the precise calculation of Pangaea’s center. Then by working backwards they are able to recreate the older supercontinents, Rodinia (~600 Mya) and Nuna (~1000 Mya).
Their results match what little understanding we do have of what these older supercontinents looked like. What is more important, however, is that authors’ method for deriving these supercontinents match movements being observed in the Earth’s mantle, and movements of the mantle in the past that have been reconstructed. Over a period of 800 Mya, Mitchell et al. are able to show the movement of Earth’s continents as they form one supercontinent into another, while also arriving at a picture that looks like Earth today. The orthoversion model also helps explain the movement of Australia, India, and Arabia. Each of those landmasses have moved eastward into the subduction girdle of post-Pangaea, and then moved northward. Only the orthoversion model can explain this movement. The orthoversion model also provides the missing link in Pangaean formation, and is the only model that matches ocean records in showing that the Pacific Ocean rift has only existed since the creation of Pangaea. By creating and presenting the orthoversion model, Mitchell et al. have shown that orthoversion explains the connection between supercontinent decline and growth, and many other gaps in the other two theories.