The striking geographical alignment of continental coastlines, especially the eastern edge of South America and the western edge of Africa, suggests a past connection between the landmasses. The modern scientific framework that explains this phenomenon is the theory of Plate Tectonics, which describes how the Earth’s rigid outer layer is broken into large, moving slabs. This theory provides a comprehensive explanation for the continents’ current arrangement and the dynamic processes that continue to shape the planet’s surface. The compelling evidence supporting this movement comes from various fields of science, including geology, paleontology, and climatology.
The Puzzle Piece Observation: Continental Drift
The concept that the continents had once been joined was first formally developed by Alfred Wegener in the early 20th century. Wegener, a German meteorologist, proposed the hypothesis of Continental Drift, suggesting that all the world’s landmasses were once consolidated into a single supercontinent. His initial and most intuitive evidence was the remarkably complementary shape of the coastlines, particularly across the Atlantic Ocean. When the continental shelf boundaries, rather than the eroded coastlines, are compared, the fit between South America and Africa becomes even more precise. He proposed that the continents, composed of lighter rock, had somehow plowed through the denser oceanic crust. This proposed mechanism, however, was fundamentally flawed and lacked a plausible physical force strong enough to move entire landmasses. Because he could not provide a convincing explanation for how the continents moved, his hypothesis was largely dismissed by the scientific community for decades.
Geological and Biological Proof of Connection
The physical and biological evidence collected by Wegener and later scientists provided static proof that the continents were once physically connected. Paleontological evidence, such as the discovery of identical fossils of specific species on widely separated continents, is particularly compelling.
For instance, the remains of Mesosaurus, a freshwater reptile that lived during the Permian period, are found only in southern Africa and eastern South America. This small creature could not have swum across the vast, saltwater South Atlantic Ocean, strongly suggesting the landmasses were joined when it lived there.
Further biological proof comes from the fossilized remains of the fern Glossopteris, which are distributed across South America, Africa, India, Australia, and Antarctica. Similarly, the distribution of other non-swimming reptiles, like Lystrosaurus, across multiple continents that are now far apart, reinforces the conclusion of a past connection.
Geological features also show remarkable continuity when the continents are reassembled. The Appalachian Mountains in the eastern United States and Canada align perfectly with similar rock structures and mountain ranges found in Greenland, the British Isles, and Scandinavia.
Ancient climatic evidence also supports the reconstruction of a single landmass located in a different position on the globe. Deposits of glacial till and evidence of glacial striations—parallel scratches on rocks caused by moving ice sheets—are found in modern-day tropical regions like parts of India and Africa. This suggests these landmasses were once situated near the South Pole, where massive ice sheets could form, and the patterns of the glacial deposits align when the continents are fitted back together. The presence of coal deposits, which form in tropical, swampy environments, in currently cold regions like Antarctica provides another line of paleoclimatic evidence for continental movement.
The Driving Force: Plate Tectonics
The question of how continents move was finally answered with the development of the theory of Plate Tectonics, which provides the missing mechanism for continental drift. The Earth’s outermost layer, the lithosphere, is a rigid shell composed of about a dozen major tectonic plates, which include both continental and oceanic crust. These plates float on the asthenosphere, a layer of the upper mantle composed of semi-molten, ductile rock that allows the plates to move slowly.
The main engine for this movement is mantle convection, a process driven by heat escaping from the Earth’s core. Hotter, less dense material in the mantle slowly rises toward the surface, cools, and then sinks back down in a continuous circulation pattern, much like water boiling in a pot. This slow motion of the mantle exerts a dragging force on the overlying tectonic plates, causing them to shift at speeds of a few centimeters per year.
Plate movement results in three main types of boundaries where plates interact.
- Divergent boundaries: Plates pull away from each other, a process seen at the Mid-Atlantic Ridge where new oceanic crust is created, continuously separating South America and Africa.
- Convergent boundaries: Plates collide, often resulting in one plate sinking beneath the other.
- Transform boundaries: Plates slide horizontally past one another.
These dynamic interactions are the continuous forces that have reshaped the continents over geological time and provide the physical explanation for the jigsaw puzzle-like fit observed today.