Supercontinent

In geology, a supercontinent is when most or all of Earth's land masses come together to form one huge continent.

Supercontinents have come together and broken apart many times in Earth's history because of plate tectonics. Right now, there isn't a true supercontinent, but the closest is the Afro-Eurasian landmass. The last time all the continents were close together was from 336 to 175 million years ago, when the supercontinent Pangaea existed.

Scientists think that in about 250 million years from now, a new supercontinent called Pangaea Proxima might form.

Theories

The Phanerozoic supercontinent Pangaea began to break apart about 215 million years ago, and this is still happening. Pangaea is the most recent supercontinent. Its pieces fit together like puzzle pieces, especially around the Atlantic Ocean.

There are two main ideas about how supercontinents formed before Pangaea. One idea says that at least two supercontinents existed, named Vaalbara and Kenorland. These broke apart around 2,480 and 2,312 million years ago. Later, parts of them came together to form Nuna. Nuna grew and eventually joined with other lands to form Rodinia. Rodinia broke apart between about 825 and 750 million years ago. Some of its pieces had already joined to form Gondwana. Pangaea later formed when Gondwana joined with Laurasia and Siberia.

The other idea says that all land was joined in one supercontinent from about 2.72 billion years ago until it broke up much later. This theory uses special magnetic evidence from rocks. It also suggests that the way Earth's plates moved was different in very early times. This idea has been questioned by many researchers.

Cycles

A supercontinent cycle is when a very big piece of land breaks apart and a new one forms. This happens all around the world. This is different from the Wilson cycle, which is about how an oceanic basin opens up and closes. Both of these cycles helped create large old landmasses like Pangaea and Rodinia.

Some slow changes on Earth's surface, such as carbonatites, granulites, eclogites, and greenstone belt bending, might tell us when old supercontinents formed and broke apart. But sometimes these changes do not clearly show the pattern of supercontinent cycles. The table below lists ancient supercontinents and when they existed, using a wider definition from 2011.

Volcanism

The movement of hot rock deep inside Earth helps push and pull the continents together and apart. When parts of the old ocean floor sink down, they can cause big movements that make new hot spots rise up. These rising spots can push the continents to come together and form supercontinents.

Hot rock rising up can also break supercontinents apart. Big outpourings of lava happen when continents break apart, but we still don’t know exactly how these lava flows change the ancient climate.

Plate tectonics

Global palaeogeography and how Earth's crust moves are well understood back to when Pangaea existed. But looking even further back is harder. Scientists study old ocean floors, coastlines, mountains, magnets in rocks, and fossils to learn about the past.

Sometimes, like when Pangaea existed, the edges of continents didn't move much. When continents break apart, new ocean floor forms. This helps us learn when supercontinents formed and broke apart. For example, when Pangaea existed, there were fewer moving edges. When Pangaea broke up, more edges started moving. Studying mountains also helps scientists understand how continents joined together. When Gondwana and Laurasia joined, they created the Variscan mountain range, which includes parts of the Appalachian Mountains. These mountains changed weather patterns around the world.

Climate

Continents have a big effect on Earth’s climate. When they come together as supercontinents, this effect becomes even stronger. Continents change wind patterns and how ocean currents flow. They also reflect more sunlight than oceans, which is called albedo. Mountains can redirect winds, and higher land can make areas cooler and drier. We can see this today in places like Eurasia. Rocks show evidence of similar conditions in the past when continents were joined together.

When continents break apart or come together, it can affect Earth’s cold periods called glacial epochs. For example, the breaking up of very old continents like Kenorland and Rodinia happened during times when Earth had long periods of cold weather. Some scientists think cold periods also happened when continents moved very slowly. During times when continents were joining together, cold periods seemed less common, but we don’t have enough evidence to say for sure. One theory suggests that when a supercontinent like Pangaea formed, its position might have allowed cold weather to happen along with high levels of a gas that helps trap heat. Even though it was very cold at the South Pole during this time, there weren’t large ice sheets for a long period.

Proxies

Granites and tiny crystals called zircons appear in rocks in patterns that show when supercontinents formed long ago. Scientists use dates from these zircons to learn about the past.

But there are some problems with using granites, like not having enough samples. When granites don’t work well, scientists look at zircons from sandstones instead. These come from big rivers and their areas. Magnetic clues from the ocean and old magnetic data help scientists learn where continents and supercontinents were about 150 million years ago. U–Pb zircon dates plutonic sandstones drainage basins