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The continents of Earth used to be united in one enormous landmass, not once, not twice, but over and over. This episode, we discuss the continuing assembly and breakup of Supercontinents.
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World Continent
The word Pangaea (or Pangea) means “all land.” The term dates back to the early 1900s when Alfred Wegener proposed the idea that all the modern continents were once joined as one: Pangaea, the supercontinent.
Image: Fama Clamosa, CC BY-SA 4.0
Later, geologists would come to realize that Wegener was right about the existence of Pangaea, although it would be decades before enough evidence was amassed to form the modern theory of plate tectonics, which explains how continents can move and oceans can open and close.
Pangaea existed between about 330 and 180 million years ago, and it left a variety of clues behind: many modern coast lines fit together quite like a puzzle; many geologic formations of the same age and composition can be found across multiple modern landmasses, having formed in the same place before being separated; the magnetic signatures of rocks can allow us to track their position on Earth through time, showing us that landmasses have come together and separated in the past; and more. Nowadays, the concept of Pangaea is scientific (and even popular) common knowledge.
But over the last few decades, scientists have noticed that many of the signs of a supercontinent show up not only during the time of Pangaea, but during several earlier times in Earth history. Pangaea, it turns out, is not the only supercontinent, just the most recent.
The Supercontinent Cycle
Top image by Alexandre DeZotti, CC BY-SA 3.0
Bottom image by John Goodge, Public Domain
It’s hard to say exactly how many supercontinents there have been. This is partly because scientists don’t all agree on what “counts” as a supercontinent – the ancient landmass of Gondwana (~600-150 million years ago), for example, was enormous, but not quite big enough for some to label it “super.” Besides that, the evidence of supercontinents can be difficult to interpret, especially for very ancient landmasses – the possible supercontinents of Vaalbara (~3.1-2.8 billion years ago), Superia (~2.7-2.4 billion years ago), and even the more recent Pannotia (~630-570 million years ago) are of somewhat uncertain size and shape, and so not all scientists agree they were truly supercontinents.
As supercontinents come together and split apart, the world changes with them. Mountains rise as continents collide and oceans open as landmasses separate; climate shifts as ocean currents change course and weather patterns adjust to the landscape;
Life, too, is impacted by supercontinents. As landmasses merge and separate, populations can become separated, sometimes leading to massive diversifications, or foreign populations can be introduced to each other, sometimes leading to intense competition. The shifting patterns of mountains, oceans, deserts, and coastlines can reshuffle living systems, and at least one mass extinction has been linked to the volcanic activity of rifting continents.
Top: Fossils of Glossopteris. Image by Daderot, Public Domain.
Bottom: Continents where Glossopteris fossils are found, including South America, Africa, Madagascar, India, Antarctica, and Australia. Image by Petter Bockman, Public Domain.
The supercontinent cycle has not ended. Even today, the breakup of Pangaea continues as the East Africa rift pulls landmasses apart. Meanwhile, the assembly of the next supercontinent has already begun, with India and various other landmasses already having collided with Eurasia, and Australia is on its way to join them. Scientists estimate the world’s next supercontinent will fully assemble in the next 200-250 million years, but exactly what shape it will take isn’t certain.
Learn More
Pangaea: Facts about an ancient supercontinent
Supercontinents 101: Pannotia, Gondwana, and Pangea
The Supercontinent Cycle
Three scientific studies that provide an overview of study of the supercontinent cycle:
Mitchell et al 2021; Nance et al 2014; Evans 2013 (open access)
How the next supercontinent will form
The Climate of Earth’s Next Supercontinent (technical, open access)
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If you enjoyed this topic and want more like it, check out these related episodes:
- Episode 122 – Plate Tectonics
- Episode 12 – The Geologic Time Scale
- Episode 113 – Paleoclimate
- Episode 124 – Snowball Earth
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