The world map presents a remarkable geographic curiosity where the coastlines of certain landmasses appear to mirror one another. This striking visual alignment, particularly noticeable across a major ocean, suggests these immense terrestrial features were once joined. This puzzle-like appearance sparked speculation among cartographers and scientists about the planet’s dynamic geological past involving the rearrangement of Earth’s surface.
The Answer: South America and Africa
The two continents that exhibit the most compelling complementary outline are South America and Africa. The eastern coastline of South America fits snugly against the western coastline of Africa. This visual correspondence is not merely a match of the current shorelines, which are constantly affected by erosion and sea level changes. The most accurate fit occurs when matching the boundaries of the continental shelves, which lie about 910 meters (3,000 feet) below sea level. This submerged boundary represents the true, stable edge of the continental crust, and when aligned, the fit is nearly perfect, with a minimal mismatch of less than 130 kilometers.
The Theory of Continental Drift
The remarkable fit provided initial evidence for the theory of continental drift, formally proposed by German meteorologist Alfred Wegener in 1912. Wegener hypothesized that continents move horizontally across the globe over geological time. While his initial ideas about the driving forces were incorrect, his concept was incorporated into the more comprehensive theory of plate tectonics. This modern theory explains that the Earth’s rigid outer layer, the lithosphere, is broken into large, rigid slabs called tectonic plates.
These plates float on the semi-fluid asthenosphere beneath them and are constantly in slow motion. The movement is powered by thermal convection within the Earth’s mantle, where hot material rises and cooler material sinks cyclically. The Atlantic Ocean represents a massive rift valley, specifically a divergent boundary where the South American and African plates are currently pulling apart. New oceanic crust is continuously formed at the Mid-Atlantic Ridge, causing the continents to spread at a rate of approximately 2.5 centimeters per year.
Matching Evidence Across the Atlantic
The theory that South America and Africa were once fused is supported by compelling evidence found across the Atlantic separation.
Paleontological Evidence
Fossils of the freshwater reptile Mesosaurus are found exclusively in specific regions of southern Africa and eastern South America. This small, aquatic creature could not have swum across the vast, saltwater Atlantic Ocean, suggesting its habitat was once connected. Fossils of the seed fern Glossopteris and the reptile Lystrosaurus are also distributed across these and other southern continents.
Geological Evidence
Geological surveys reveal a seamless continuity of rock formations and ancient mountain belts between the two continents. Mountain ranges in South Africa align perfectly with ranges found in Argentina when the continents are reassembled. Cratons, the stable, ancient cores of the continents, show identical structures and ages on both sides of the ocean basin. This matching geology indicates that these rock layers were formed together as a single, uninterrupted unit.
Glacial Evidence
Supporting evidence comes from the distribution of glacial deposits from the late Paleozoic Ice Age, around 300 million years ago. Scratches and deposits left by massive sheets of ice, known as till, are found in present-day tropical regions of both Africa and South America. These deposits indicate that the continents were positioned much closer to the South Pole at that time. The existence of these three distinct lines of evidence validated Wegener’s initial observation.
Contextualizing the Fit: The Supercontinent Pangea
The tight fit of South America and Africa represents a fracture point within the much larger, singular landmass known as the supercontinent Pangea. Pangea, meaning “all lands” in ancient Greek, was the most recent supercontinent, having assembled roughly 335 million years ago during the Carboniferous period. At its greatest extent, Pangea encompassed nearly all of the world’s continental crust.
The separation began around 200 million years ago, with Pangea first splitting into a northern supercontinent, Laurasia, and a southern supercontinent, Gondwana. South America and Africa were both part of Gondwana, which also included modern-day Antarctica, Australia, and India. The rifting that formed the South Atlantic Ocean, separating South America from Africa, occurred during the Cretaceous period, approximately 140 million years ago.