In 1912, when Wigner proposed the "continental drift" hypothesis, he pointed out that the several continents surrounding the Atlantic Ocean today were actually separated by the rupture of a supercontinent (known as the "Pangaea" or "United Palaeoland") hundreds of millions of years ago. It took more than half a century for this view to be gradually accepted by most earth scientists. Scientists have discovered that between 300 million and 250 million years ago, all continents on earth once came together to form the Pangaea. The Pangea consists of Gondwana in the south (including present-day Australia, India, Antarctica, South America and Africa) and Laua in the north (including present-day North America, Greenland and Eurasia).
As research continues to deepen, scientists have discovered that similar supercontinents exist in other periods in Earth's history, such as the earliest known continent, Ur, about 3 billion years ago, and Kenoran, Colombia, 1.8 billion to 1.5 billion years ago, 1.1 billion to 750 million years ago, etc. In the 1980s, Professor Nance of Ohio University and his collaborators also proposed the hypothesis of "supercontinental cycles". They believe that due to the periodic convergence and divergence of plates, the continents on the earth will undergo a process of aggregation and division every 400 million years. However, current evidence shows that supercontinents have existed for varying lengths of time and do not have a very uniform cycle; paleogeographic reconstruction results also show that some continents have existed for far more than 500 million years. Therefore, the "supercontinental cycle" hypothesis has not yet been fully accepted.
According to the theory of plate tectonics, the lithosphere is divided into plates that float on the asthenosphere at the top of the mantle, like fragmented ice floating on the water. These plates move at a rate of a few centimeters per year. At present, most researchers believe that the aggregation and disintegration of supercontinents are the result of plate movement. So why did the supercontinent split? Scientists believe that the rocks that make up continents are not as dense and thicker as the crust that makes up the ocean, so they have relatively poor thermal conductivity and block heat from escaping from the mantle like an insulating layer. When continents gather together to form a supercontinent, it is like putting a thick cotton pad on top of the "electric blanket" of the mantle, and more heat will naturally gather under the supercontinent. As heat continues to accumulate and the material at the bottom of the lithosphere becomes less dense, causing the overlying supercontinent to rise upward and rupture. There is also a view that at the core-mantle boundary below the supercontinent, a hot material upwelling thousands of kilometers in diameter will form, known as a "super mantle plume." Under the temperature and pressure of the "super mantle plume", the lithosphere of the supercontinent will become fragile, and eventually the mantle plume will break through the rocks, rupturing the supercontinent.
After the supercontinent ruptures, the broken part moves to both sides driven by mantle convection. A large amount of hot magma from the asthenosphere is ejected from the rift, and the rift becomes an expansion center. Magma continues to eject and form new ocean crusts, new oceans expand and continents drift to both sides. As time goes by, the density of the new ocean crust will become larger and larger; when the density reaches a certain level, the resistance of the adjacent continental crust is overcome, and the ocean crust will subduct under the continental crust. The continent continues to drift to both sides. After a certain extent, two possibilities will emerge: long-term subduction will eventually lead to the disappearance of the ocean crust in the middle, the new ocean will close again, the continent will re-gather and merge, creating a new almost in situ. supercontinent; Another possibility is that during the separation of the continent to both sides, the ocean crust on the outer side of the continent (both sides) subducted under the continental crust, eventually leading to the disappearance of the outer ocean crust and ocean, and the continent gathered on the other side of the earth, creating a new supercontinent.