Earth & Space Science: Session 2
A Closer Look: Supercontinents
Where did the idea of supercontinents come from?
Long before the theory of plate tectonics became accepted, there was much speculation that the present day continents were the fragmented pieces of pre-existing larger landmasses called supercontinents. The belief that the modern continents have not always been in their present positions has long been held. As early as the 1500s, many geographers and mapmakers noticed the close match of the coastlines of South America and Africa. The fit is even more striking when the continental shelves (submerged edge of a continental plate) and the continental slopes (the true boundary of a continent) are compared rather than the coastlines. It was not until 1912, however, that the idea of moving continents was seriously considered as a scientific theory. This theory, called continental drift theory, was the precursor to plate tectonics theory and was introduced by Alfred Wegener.
How do scientists describe the history of supercontinents on Earth?
Scientists believe there have been several supercontinental arrangements in the history of the Earth. The first known supercontinent is called Rodinia (from Russian, meaning "homeland"), and it is thought to have formed about 1.1 billion years ago. Although the exact size and configuration of Rodinia cannot be estimated, rocks of ancestral North America are thought to have formed the core of the giant continent. About 750 million years ago, evidence suggests that Rodinia fragmented into pieces that drifted apart. Approximately 600 million years ago, those pieces collided again forming a new supercontinent, Pannotia.
Scientists think Pannotia broke up about 550 million years ago into several smaller fragments: Laurentia (the core of what is now North America), Baltica (northern Europe), other small fragments, and one very large fragment called Gondwanaland, which contained the land from modern day China, India, Africa, South America, and Antarctica. Between 550 and 350 million years ago, Laurasia, a landmass comprised of North America and Eurasia, was formed. Laurasia and Gondwanaland then joined to form the supercontinent of Pangaea (from classical Greek, meaning "all lands"). Evidence suggests that Pangaea began to break up about 225 million years ago, and continues to separate into the modern continents we know today.
The process of supercontinent assembly, breakup, dispersal and re-assembly takes, on average, about 500 million years. This supercontinent cycle is called the Wilson Cycle after J. Tuzo Wilson, the Canadian geologist who first described it.