The idea that the Earth’s continents might not be fixed in place, but had once been joined in a single supercontinent named Pangaea, represented a profound shift in scientific thought. Before this concept, geologists largely assumed the continents and ocean basins had always existed in their current positions. The notion of continents “drifting” across the globe was first spurred by a series of geographical and empirical observations. These clues, drawn from maps, fossils, and rock formations, challenged the fixed-Earth model and forced researchers to question the planet’s ancient geography.
The Visual Clue of Matching Coastlines
The first suggestion that continents had moved came from the visual observation of complementary shapes on opposite sides of the Atlantic Ocean. Cartographers and explorers, as early as the 16th century, noted the striking jigsaw-puzzle fit, particularly between the eastern coast of South America and the western coast of Africa. While this fit was visually suggestive, it remained a curiosity rather than a scientific hypothesis for centuries. The actual coastlines are constantly eroded, but if one traces the continental shelf—the submerged edge of the continent—the fit between South America and Africa becomes even more precise.
Fossil Distribution and Geological Alignment
The visual fit gained scientific weight when researchers began finding identical biological and geological evidence across vast ocean barriers. These findings demonstrated that widely separated landmasses must have once been directly connected. The organisms and rock structures found could not have crossed the intervening oceans, providing strong empirical support for movement.
Paleontological Evidence
One convincing line of evidence came from the distribution of specific, ancient fossils incapable of crossing saltwater oceans. For instance, the remains of Mesosaurus, a freshwater reptile, are found only in specific regions of South Africa and South America. Since this shallow-water creature could not survive in the deep ocean, its presence on two continents strongly suggested a former land connection. Fossils of land-dwelling reptiles like Lystrosaurus and Cynognathus are similarly distributed across Africa, India, Antarctica, and South America, along with the Glossopteris flora. The only logical explanation for these non-contiguous fossil distributions was that the landmasses had once been united in a single continent.
Geological Evidence
Beyond the fossils, specific rock formations and mountain chains show remarkable continuity across continents now separated by oceans. Identical rock types, structures, and ages appear on both sides of the Atlantic, suggesting they formed side-by-side. For example, the Appalachian Mountains align perfectly with mountain ranges in Greenland, Great Britain, and Norway. When the continents are reassembled, these matching mountain belts form a single, coherent geological structure. Furthermore, ancient glacial deposits, known as tillites, are found in tropical locations like South America, Africa, India, and Australia, suggesting these landmasses were once clustered near the South Pole.
The Hypothesis of Continental Drift
The German geophysicist and meteorologist Alfred Wegener was the first to synthesize these diverse observations into a formal scientific hypothesis in the early 20th century. He compiled the evidence of coastal fit, fossil distributions, and matching geological structures into a coherent model he called “Continental Drift.” Wegener proposed that all continents had once been locked together in a single supercontinent named Pangaea, which broke apart about 200 million years ago. Despite the compelling nature of his evidence, his hypothesis faced significant skepticism because he could not propose a plausible physical mechanism to explain how continents moved. This lack of a driving force meant the idea remained a hypothesis until later discoveries provided the missing mechanisms, leading to the modern theory of plate tectonics.