Breakup of Pangaea: How the Atlantic Ocean Was Born

The breakup of Pangaea was the slow splitting of Earth’s last supercontinent, which began about 200 million years ago at the end of the Triassic Period. Over the next 150 million years and more, Pangaea divided into a northern landmass called Laurasia and a southern one called Gondwana, and the Atlantic Ocean opened between them. The process shaped the modern map of the world, the distribution of plants and animals, and the history of life itself.

Background: the supercontinent Pangaea

Pangaea assembled during the late Paleozoic Era as earlier continents collided. By around 300 million years ago, almost all of Earth’s land formed a single mass stretching from pole to pole, surrounded by a world ocean known as Panthalassa. A wedge-shaped sea called the Tethys Ocean cut into its eastern side.

The name means “all lands” in Greek. It was used by the German scientist Alfred Wegener, who argued in 1912 and in his 1915 book Die Entstehung der Kontinente und Ozeane (The Origin of Continents and Oceans) that the continents had once been joined. His theory of continental drift was widely rejected at the time, largely because he could not explain what force moved the continents.

Why the supercontinent broke apart

Modern geology explains the breakup through plate tectonics. Earth’s outer shell is divided into rigid plates that move slowly over the hotter, softer mantle below. A large supercontinent acts like an insulating blanket, and heat can build up in the mantle beneath it.

Stretching forces and rising hot mantle material weakened the crust of Pangaea. Long valleys called rifts formed where the crust thinned and dropped down between faults. In the Late Triassic, from roughly 230 million years ago, a chain of rift basins opened along the zone between eastern North America and north-west Africa. Examples include the Newark Basin of New Jersey and Pennsylvania and the Fundy Basin of Nova Scotia, which filled with river and lake sediments.

How the Atlantic opened

Around 201 million years ago, a vast pulse of volcanism, the Central Atlantic Magmatic Province, flooded the rift zone with basalt across what is now North America, South America, Africa and Iberia. This event coincided with the Triassic–Jurassic extinction, which helped dinosaurs rise to dominance.

The crust eventually broke completely, and new ocean floor began forming between North America and Africa. Estimates for the start of true sea-floor spreading in the Central Atlantic vary, but are commonly placed in the Early to Middle Jurassic, roughly 190 to 175 million years ago. The oldest Atlantic ocean crust lies off the eastern coast of the United States and north-west Africa. Thick salt deposits along both margins record an early stage when seawater repeatedly flooded and evaporated in the narrow young basin.

At about the same time, the Gulf of Mexico opened as North and South America moved apart. The Tethys Ocean connected with the young Atlantic, and Laurasia and Gondwana became separated by a belt of sea.

The breakup of Gondwana and Laurasia

Gondwana itself began to fragment in the Jurassic. Around 183 million years ago, large eruptions known as the Karoo and Ferrar provinces affected southern Africa and Antarctica, and East Gondwana, made up of Antarctica, India, Madagascar and Australia, started to separate from Africa.

The South Atlantic opened from the south in the Early Cretaceous, from roughly 140 to 130 million years ago, as South America and Africa pulled apart. Flood basalts of the Paraná and Etendeka provinces, now found in Brazil and Namibia, erupted during this phase. India separated from Madagascar around 90 million years ago and moved rapidly north, colliding with Asia around 50 million years ago to begin raising the Himalayas.

In the north, Laurasia broke up more slowly. Greenland and Europe separated around 55 million years ago, accompanied by volcanism that left basalts in Scotland, Northern Ireland and the Faroe Islands. Australia separated from Antarctica in stages between about 85 and 35 million years ago, and the opening of the Drake Passage between South America and Antarctica later helped isolate Antarctica and allow its ice sheet to grow.

Evidence for the breakup

The fit of the coastlines of South America and Africa was noticed after the first accurate maps were made, and in 1965 Edward Bullard and colleagues used a computer to show that the continents fit closely along the edges of their continental shelves. Fossils provide further evidence. The seed fern Glossopteris and the reptiles Mesosaurus and Lystrosaurus are found on southern continents now separated by oceans.

The South African geologist Alexander du Toit strengthened Wegener’s case in his 1937 book Our Wandering Continents, matching rock formations across the South Atlantic and naming the northern landmass Laurasia. The name Gondwana had earlier been introduced by the Austrian geologist Eduard Suess, after a region of central India.

Decisive proof came from the sea floor. In the 1950s and 1960s, surveys revealed the Mid-Atlantic Ridge, a mountain chain running down the middle of the ocean, and stripes of magnetised rock on either side that record reversals of Earth’s magnetic field. The pattern showed that new crust forms at the ridge and spreads outwards, a key part of the plate tectonics revolution. Deep-sea drilling later confirmed that the ocean floor becomes older with distance from the ridge.

Effects on climate and life

The breakup did not happen in isolation from the living world. Each major phase of rifting was accompanied by large volcanic eruptions, and several coincided with environmental crises. The Central Atlantic eruptions match the end-Triassic extinction, and the Karoo–Ferrar eruptions coincide with a period of ocean oxygen loss in the Early Jurassic, known as the Toarcian oceanic anoxic event, about 183 million years ago.

As the continents separated, new coastlines and shallow seas formed. Sea levels were high through much of the Jurassic and Cretaceous, and warm, shallow seas spread over parts of North America, Europe and Africa. Many of the limestones and chalks of western Europe, including the white cliffs of southern England, were laid down in such seas during the Cretaceous.

Separation also isolated animal and plant populations. Dinosaurs in the Late Cretaceous show increasingly distinct groups on different continents. Later, mammals evolved along separate paths: marsupials diversified in Australia and South America, while Africa produced its own lineages such as elephants and their relatives. Changes in ocean gateways, such as the opening of the Drake Passage and the separation of Australia from Antarctica, redirected ocean currents and influenced global climate, contributing to the cooling that led to Antarctic glaciation around 34 million years ago.

Timeline

• c. 300 million years ago: Pangaea is largely assembled as a single supercontinent.
• c. 230 million years ago: Rift basins begin forming between North America and north-west Africa.
• c. 201 million years ago: The Central Atlantic Magmatic Province erupts, coinciding with the end-Triassic extinction.
• c. 190–175 million years ago: Sea-floor spreading opens the Central Atlantic, separating Laurasia from Gondwana.
• c. 183 million years ago: Karoo and Ferrar volcanism accompanies the start of Gondwana’s breakup.
• c. 140–130 million years ago: The South Atlantic begins to open between South America and Africa.
• c. 55 million years ago: Greenland and Europe separate as the North Atlantic opens.
• 1912: Alfred Wegener presents his theory of continental drift.
• 1937: Alexander du Toit publishes Our Wandering Continents.

Why it matters

The breakup of Pangaea created the Atlantic Ocean and set the continents on the paths that produced today’s geography. By isolating landmasses, it allowed plants and animals to evolve separately, helping to explain why Australia, South America and Africa have such distinctive wildlife. Its rift basins and continental margins also hold many of the world’s oil, gas and salt deposits, and the Atlantic continues to widen by a few centimetres every year.