Introduction
The Continental Drift Theory was formally postulated by German meteorologist Alfred Wegener in 1912, building on earlier observations by Abraham Ortelius and Antonio Snider-Pellegrini. Wegener proposed that all continents originally formed a single supercontinent called Pangea, surrounded by a mega-ocean named Panthalassa. Around 200–250 million years ago during the Mesozoic era, Pangea rifted into Laurasia and Gondwanaland, eventually fragmenting and drifting into today's continental configurations.
Evidences Supporting Continental Drift
- The Jig-Saw Fit: The coastlines of South America and Africa exhibit a striking complementary match. This matching was statistically and cartographically confirmed by Edward Bullard’s 1964 computer-generated fit at the 500-fathom (depth) contour line.
- Paleoclimatic Evidence (Glacial Tillites): Sedimentary deposits of glacial origin (tillites) dating to the Carboniferous period reveal identical stratigraphic sequences across scattered Gondwana landmasses, including peninsular India, southern Africa, Madagascar, Antarctica, and Australia, indicating shared paleolatitudes.
- Fossil Correlations: Identical terrestrial and freshwater fossils occur across vast oceans: Mesosaurus (a small freshwater reptile found only in South Africa and eastern South America), Lystrosaurus (found in India, Africa, and Antarctica), and the widespread deciduous seed fern Glossopteris.
- Geological and Placer Deposits: Rich gold placer deposits found along the Ghana coast in West Africa lack local source rock formations; the corresponding gold-bearing quartz veins occur across the Atlantic in Brazil.
Proposed Driving Forces and Associated Criticisms
To explain the mechanism of continental motion, Wegener suggested two principal natural forces:
- Pole-Fleeing Force (Polfluchtkraft): Caused by the centrifugal force of the Earth's rotation, supposedly driving landmasses equatorward.
- Tidal Force: Caused by the gravitational attraction of the Moon and the Sun, supposedly dragging continents westward.
Physicists and geologists (notably Harold Jeffreys) fundamentally rejected these driving forces, proving through rigorous calculations that the tidal and centrifugal forces were millions of times too weak to displace massive continental sial over dense oceanic sima. Furthermore, Wegener could not explain how continents could plough through the oceanic floor without undergoing severe deformation.
Conclusion
Although Wegener's driving mechanism was untenable, his empirical evidence for continental displacement was remarkably robust. His foundational work catalyzed subsequent geoscientific breakthroughs, notably Arthur Holmes' mantle convection hypothesis, Harry Hess's Sea-Floor Spreading theory, and the unifying paradigm of Plate Tectonics, which established that oceanic crust is continuously created at mid-ocean ridges and is substantially younger than continental crust.