Alfred Wegener, a German meteorologist and geophysicist, formally introduced his hypothesis of Continental Drift in 1912, challenging the prevailing geological understanding of Earth’s surface. His idea proposed that the continents were not fixed but had slowly moved across the globe over geologic time. Wegener proposed that around 300 million years ago, all the Earth’s landmasses were merged into a single supercontinent he named Pangaea (“all lands”). This immense landmass then began to fracture and drift apart, leading to the configuration of continents seen today. Wegener compiled a comprehensive collection of evidence drawn from various scientific disciplines to support this displacement.
The Apparent Fit of Continents
The most immediate and visually compelling evidence Wegener used was the remarkable congruency of the continents’ coastlines. He noted how the eastern coast of South America and the western coast of Africa appeared to fit together like pieces of a massive jigsaw puzzle. This observation was central to his argument for a former supercontinent.
Wegener refined this fit by looking beyond the present-day shorelines, which are constantly altered by erosion and sea level changes. He proposed that the true edges lay at the boundary of the continental shelf, a submerged extension of the landmass. When mapped at this deeper contour, the fit between South America and Africa became nearly perfect, suggesting they were once a singular block of continental crust.
Matching Geological Structures Across Oceans
Wegener analyzed the geology of landmasses separated by vast oceans, finding striking similarities in rock types and structural features. He reasoned that if the continents were once joined, ancient mountain chains and rock layers should align seamlessly across the fracture lines. This prediction proved accurate when examining the regions bordering the North Atlantic.
The ancient mountain belts of the Appalachian Mountains in the eastern United States and Canada showed a direct correlation with structures found in eastern Greenland, the British Isles, and Scandinavia. These mountain systems, sharing a similar age and composition, form a continuous chain (the Appalachian-Caledonian system) when the continents are reassembled. Furthermore, Wegener found identical sequences of rock strata, including ancient crystalline basement rock and sedimentary layers, in Brazil and South Africa. This continuity implied a former connection that was later broken by continental movement.
Fossil Distribution Patterns
Wegener’s theory was strongly supported by the distribution of ancient fossils across continents now separated by thousands of miles of ocean. These fossils belonged to land-dwelling or freshwater organisms, making it highly improbable they could have crossed saltwater ocean basins. The presence of identical species on widely separated continents suggested the landmasses were once connected, allowing free migration.
A prime example is the freshwater reptile Mesosaurus, whose fossils are found exclusively in Permian-age rocks in both South America and southern Africa. Since this small reptile could not have swum across the Atlantic, its scattered fossil record indicated a continuous habitat that was later divided.
Similarly, fossils of the land-dwelling reptile Lystrosaurus are discovered in Africa, India, and Antarctica. The widespread distribution of this relatively slow-moving reptile points directly to a time when these southern continents were linked. The ancient seed fern Glossopteris is also found across all the southern continents, including Antarctica, Australia, India, South America, and Africa.
Evidence from Ancient Climate Indicators
The final evidence Wegener presented involved paleoclimatology, the study of Earth’s past climates. He examined rock deposits that only form under specific climatic conditions, finding them in places where the current climate could not have produced them. This mismatch could only be reconciled by the movement of the continents across latitude lines.
One major finding was the widespread presence of glacial deposits, such as tillites and glacial striations, in tropical landmasses like India, southern Africa, South America, and Australia. These features are remnants of an extensive ancient ice sheet that covered a large portion of Pangaea’s southern section. Placing these continents together near the South Pole provides a logical explanation for the vast glaciation that occurred approximately 300 million years ago.
Conversely, Wegener pointed to the discovery of extensive coal deposits in Antarctica, which form exclusively from the dense vegetation of tropical swamps and rainforests. This indicated that Antarctica must have once been located near the equator, supporting the conclusion that the continents had drifted over geological time.