What was Pangaea? The supercontinent, and how we know

Pangaea was a supercontinent: nearly all of Earth's land joined in one mass, surrounded by a single world ocean called Panthalassa. It came together about 335 million years ago and began to split about 200 million years ago, and its pieces drifted apart into today's continents, opening the Atlantic as they went. The name, Greek for "all lands", comes from Alfred Wegener, who argued for it in 1912, decades before anyone could explain how continents move.

In short

• Pangaea lasted roughly 135 million years, long enough for the first dinosaurs to evolve on it and spread across it on foot.
• Wegener's evidence was strong: coasts that fit, matching fossils and rocks, and glacial scars in the tropics. What he lacked was a mechanism.
• The mechanism, seafloor spreading, came from mapping the ocean floor in the 1950s and 1960s, and Pangaea was only the latest of several supercontinents.

What did Pangaea look like?

Pangaea was shaped roughly like a C, stretching from near the North Pole to near the South Pole. Its northern half, later called Laurasia, held what became North America, Europe and most of Asia. Its southern half, Gondwana, held South America, Africa, Antarctica, Australia and India. Inside the curve of the C lay a warm sea, the Tethys. Everything else was Panthalassa, an ocean larger than the Pacific is today.

The interior was far from any coast, so much of it was hot and dry, with deserts on a scale no continent has now. A long chain of mountains ran through its middle where the continents had collided, and the worn-down stumps of those mountains survive on both sides of the Atlantic, as the Appalachians in North America and the mountains of Scotland and Norway.

When did Pangaea form and break up? A timeline

All dates are approximate, in millions of years ago; Wikipedia's summary of the research gives 335 million for the assembly and the U.S. Geological Survey gives 225 to 200 million for the start of the breakup.

When	What happened
About 335 million years ago	Gondwana collides with the northern continents, and Pangaea is largely assembled
About 300 million years ago	Ice sheets cover the southern part of Pangaea, near the South Pole
About 252 million years ago	The largest mass extinction in Earth's history, at the end of the Permian, happens while Pangaea is whole
About 230 million years ago	The first dinosaurs appear, on a single landmass they can walk across
About 200 million years ago	Rifts open between North America and Africa; huge outpourings of lava follow; the breakup begins
About 180 million years ago	The central Atlantic is opening; Laurasia and Gondwana separate
About 130 million years ago	South America and Africa pull apart, opening the South Atlantic
About 50 million years ago	India, having crossed the ocean, collides with Asia and begins to raise the Himalayas
Today	The breakup continues in the East African Rift and the Red Sea

The breakup shaped the living world. Once the land split, animals and plants on each piece evolved separately, which is part of why Australia, isolated for tens of millions of years, has its own marsupials and why South America and Africa share ancient groups but not recent ones. The note on how evolution works explains how isolation makes species diverge. And the dinosaurs' 165-million-year story, from their start on Pangaea to what killed them, played out as their world came apart.

What was Wegener's evidence?

Alfred Wegener, a German meteorologist and polar explorer, first presented continental drift in a lecture in Frankfurt on 6 January 1912 and set it out in his 1915 book The Origin of Continents and Oceans. He gathered four kinds of evidence, and each one was hard to explain if the continents had always been where they are.

Evidence	What is found	What Pangaea explains
The fit of the coasts	The bulge of Brazil fits into the curve of West Africa, and the fit is even better at the edge of the continental shelves	They were once one coastline, torn apart
Fossils	Mesosaurus, a small freshwater reptile, only in Brazil and southern Africa; the seed fern Glossopteris across South America, Africa, India, Antarctica and Australia; the reptile Lystrosaurus in Africa, India and, found in 1969, Antarctica	A freshwater animal couldn't swim an ocean; the continents were joined when it lived
Rocks and mountains	Rock layers, mountain belts and coal beds that stop at one coast and continue on the other	They formed as one, then split
Ancient ice	Scratches and deposits from glaciers about 300 million years old in now-tropical India, Africa and South America, with scratch directions that only make sense with the continents put back together	Those lands were then clustered near the South Pole

The usual rival explanation for the fossils was that land bridges had once linked the continents and then sank. Wegener pointed out that continents are made of lighter rock than the ocean floor and float higher on the mantle, so a slab of continent couldn't simply sink out of sight. That argument holds today.

Why did geologists reject continental drift?

Wegener had good evidence that the continents had moved but no believable explanation of how. He proposed that continents plowed through the ocean floor, pushed by forces from Earth's spin and the pull of the Sun and Moon. Physicists, led in Britain by Harold Jeffreys, calculated that those forces were far too weak, and that solid continents couldn't plow through solid ocean crust. Many geologists, especially in North America, also resented an outsider redrawing their field. According to NASA's profile of Wegener, the president of the American Philosophical Society called the idea "utter, damned rot."

Wegener kept revising the book until 1929. He died on the Greenland ice sheet in November 1930, on an expedition, with his theory largely dismissed. There was a better mechanism already on the table: in the 1930s, the British geologist Arthur Holmes suggested that slow convection in the mantle could carry continents along. It drew little attention at the time.

What finally proved it?

The proof came from the ocean floor, which Wegener never saw. Three discoveries, each pointing the same way, settled it:

1. Rock magnetism, the 1950s. When lava cools, its iron minerals record the direction to the magnetic pole. Rocks from Europe and North America pointed to different past positions of the pole, which made no sense unless the continents had moved. Close the Atlantic, and the two records line up.
2. Seafloor spreading, 1960–62. Harry Hess and Robert Dietz proposed that new ocean floor forms at mid-ocean ridges and moves outward. That replaced plowing continents with a moving floor that carried them.
3. Magnetic stripes, 1963. Earth's magnetic field flips every so often. Fred Vine and Drummond Matthews, and separately Lawrence Morley, showed the ocean floor has stripes of rock magnetized in alternating directions, mirrored on either side of the ridges, like a tape recording made as the floor spread.

Drilling then showed the ocean floor gets older with distance from the ridges, and almost nowhere older than about 200 million years. By the end of the 1960s these pieces had become plate tectonics. Wegener's coasts and fossils were right; his mechanism was wrong. The continents don't plow through the ocean floor; they ride on plates that include it.

Were there supercontinents before Pangaea, and will there be another?

Pangaea is the most recent supercontinent, not the only one. Geologists think the continents gather and scatter in a cycle of several hundred million years. Before Pangaea there was Rodinia, which came together roughly 1.1 billion years ago and began breaking apart about 750 million years ago, and before that Columbia, also called Nuna, assembled about 2 billion years ago. The older the supercontinent, the less certain its shape, because the evidence has been folded, eroded or destroyed since.

The next one is a matter of models, not forecasts. Projecting today's plate motions forward, different teams have drawn different futures: Pangaea Proxima or Pangaea Ultima, closing the Atlantic in about 250 million years; Amasia, joining the Americas and Asia across the Arctic; and others, which depend on which oceans close. A 2023 study in Nature Geoscience modeled Pangaea Ultima's climate and found its interior could become too hot for most mammals. These are scenarios built on assumptions about forces still not fully understood, not predictions of a date.

Check yourself

• Without looking back: which piece of Wegener's evidence is hardest to explain with land bridges, and why?
• What did Wegener get right, and what did he get wrong?
• How do the magnetic stripes on the ocean floor record the ocean's spreading?

Sources

• Historical perspective, in This Dynamic Earth — U.S. Geological Survey
• Developing the theory, in This Dynamic Earth — U.S. Geological Survey
• Alfred Wegener — NASA Earth Observatory
• Climate extremes likely to drive land mammal extinction during next supercontinent assembly — Farnsworth and others, Nature Geoscience, 2023
• Pangaea — Wikipedia