The visual suggestion that two continents fit together like puzzle pieces was a foundational observation for modern earth science. Mapmakers and geographers observed this striking geographic coincidence for centuries. However, it was not until the early 20th century that a formal theory used this observation as evidence of a dynamic planet. This apparent match became the first piece of a much larger scientific mystery about the deep history of Earth’s landmasses, leading to the revolutionary understanding of how continents move and oceans form over geologic time.
The Iconic Fit: South America and Africa
The two continents that share this famous, interlocking boundary are South America and Africa. Their eastern and western coastlines appear to mirror each other across the South Atlantic Ocean. This resemblance is more than a simple coastal alignment, which can be distorted by erosion and sediment deposition. The true fit occurs when comparing the shape of the continental shelves, which represent the actual, submerged edges of the continental crust.
When mapped at a depth of about 1,000 meters below sea level, the corresponding shapes of the two continents align with remarkable precision. For instance, the bulge of Brazil tucks neatly into the curve of the Gulf of Guinea on the African side. The near-perfect fit of these submerged margins suggests the two landmasses were once physically joined together. This geographical congruence was the most immediate visual clue that Earth’s surface was not static.
The Theory of Continental Drift
The remarkable geographic match provided the spark for Alfred Wegener, a German meteorologist, to propose the theory of Continental Drift in 1912. Wegener hypothesized that all continents were once assembled into a single, colossal landmass he named Pangaea, meaning “all lands” in Greek. He argued that this supercontinent existed roughly 200 to 300 million years ago before beginning to fracture and drift apart.
Pangaea first split into two major sections: Laurasia to the north and Gondwana to the south. South America and Africa were integral parts of the southern supercontinent, Gondwana. Wegener suggested that continents plowed through the oceanic crust, but he lacked a credible physical mechanism to explain the required force. Despite initial skepticism due to this missing mechanism, his theory provided the historical framework for the puzzle-piece observation.
Geological and Fossil Evidence
The visual alignment was strongly supported by non-coastal evidence found on both South America and Africa, pointing to a shared geologic history. Scientists discovered identical mountain ranges and rock strata on opposing sides of the Atlantic, suggesting a continuous formation that was later severed. Ancient rock layers and mineral deposits in Brazil, for example, match those found in West Africa. This geological continuity also included evidence of ancient glaciation, where glacial deposits of the same age were found in tropical parts of both continents.
Fossil discoveries provided even more compelling proof that an ocean had not always separated the two continents. Fossils of the freshwater reptile Mesosaurus are found exclusively in southern Africa and eastern South America. Since this small, crocodile-like animal could not swim across a vast, salty ocean, its presence on both continents proves the landmasses were connected. Furthermore, the fossilized remains of the seed fern Glossopteris are found across several continents:
- South America
- Africa
- India
- Antarctica
- Australia
This plant’s large, fragile seeds could not have been dispersed across current ocean distances, confirming the existence of the single southern landmass, Gondwana.
The Engine: How Plate Tectonics Caused the Split
The actual force responsible for separating South America and Africa is explained by the modern theory of Plate Tectonics, which refined Wegener’s original concept. This process is driven by heat-generated convection currents within the Earth’s mantle. Hot, less dense material rises while cooler, denser material sinks, creating a slow circulation that moves the rigid tectonic plates floating above.
The split began when a zone of rifting—a divergent boundary—formed within Pangaea approximately 200 million years ago. As the mantle currents pulled the crust apart, magma welled up from below, creating a new ocean floor through seafloor spreading. This rifting zone eventually formed the Mid-Atlantic Ridge, a massive underwater mountain range running down the center of the Atlantic Ocean. The continuous formation of new crust at this ridge pushes the South American and African plates further apart at a rate of a few centimeters per year, continually widening the Atlantic Ocean.