Model Answer
0 min readIntroduction
The concept of continents not being fixed in their present positions has roots in early cartographic observations. However, it was Alfred Wegener, a German meteorologist, who formally proposed the theory of Continental Drift in his 1912 publication, “The Origin of Continents and Oceans.” This revolutionary idea suggested that continents were once joined together in a single supercontinent, Pangaea, and have gradually drifted apart over millions of years. The formulation of this theory wasn’t sudden; it was a culmination of various observations and evidence gathered over decades, challenging the prevailing geosynclinal theory of mountain building.
Geological Evidence: The Jigsaw Puzzle
One of the most striking pieces of evidence supporting continental drift was the remarkable fit of the continents, particularly the coastlines of South America and Africa. This ‘jigsaw puzzle’ fit was first noted by Abraham Ortelius in 1596, and later by Francis Bacon in 1620. However, the fit is even more precise when considering the edges of the continental shelves, which lie beneath the ocean. This suggests that these continents were once physically connected.
Paleontological Evidence: Shared Fossil Records
The distribution of identical fossil species across widely separated continents provided strong evidence for a past connection. For example:
- Mesosaurus: Fossils of this freshwater reptile have been found only in South America and Africa. It’s highly improbable that Mesosaurus could have crossed the vast Atlantic Ocean.
- Glossopteris: Fossils of this seed fern are found in South America, Africa, India, Australia, and Antarctica. Its seeds were too heavy to be dispersed by wind across such distances.
- Cynognathus & Lystrosaurus: These land-dwelling reptiles were found in South America, Africa, and Antarctica, further supporting the idea of a connected landmass.
These fossil distributions strongly suggest that these continents were once part of a single landmass, allowing these species to roam freely.
Paleoclimatic Evidence: Ancient Glacial Deposits & Coal Fields
Evidence of past climates also supported the theory.
- Glacial Striations: Evidence of ancient glaciation (glacial striations, till deposits) found in South America, Africa, India, and Australia suggested that these continents were once located closer to the South Pole. The direction of glacial movement also aligned if the continents were joined.
- Coal Deposits: Extensive coal deposits, formed from ancient tropical swamps, are found in North America, Europe, and Asia. This indicates that these regions were once located closer to the equator.
The presence of these climatic indicators in seemingly disparate locations could only be explained by a shift in continental positions.
Geophysical Evidence & Other Supporting Observations
While not immediately available to Wegener, later geophysical evidence solidified the theory:
- Paleomagnetism: Studies of the magnetic properties of rocks revealed that continents had moved relative to the Earth’s magnetic poles over time. Apparent polar wander paths differed for different continents, indicating that the continents themselves had moved.
- Seafloor Spreading: The discovery of mid-ocean ridges and the process of seafloor spreading, as proposed by Harry Hess in the 1960s, provided a mechanism for continental drift.
- Earthquake and Volcano Distribution: The concentration of earthquakes and volcanoes along specific belts, coinciding with the boundaries of tectonic plates, further supported the idea of a dynamic Earth.
Wegener’s initial proposal lacked a convincing mechanism to explain *how* continents could move through the oceanic crust. This was a major point of criticism. He proposed that continents ‘plowed’ through the ocean floor, which was physically implausible. It wasn’t until the development of the theory of Plate Tectonics in the 1960s that a viable mechanism – convection currents in the mantle – was established.
| Evidence Type | Description |
|---|---|
| Geological Fit | Precise matching of continental coastlines and continental shelf edges. |
| Paleontological | Identical fossil species found on widely separated continents. |
| Paleoclimatic | Evidence of past glaciation and tropical climates in unexpected locations. |
| Geophysical | Paleomagnetic data and seafloor spreading patterns. |
Conclusion
The formulation of the Continental Drift Theory was a landmark achievement in geological science. While initially met with skepticism due to the lack of a plausible mechanism, the accumulation of geological, paleontological, and paleoclimatic evidence, coupled with later geophysical discoveries, ultimately led to its acceptance. The theory paved the way for the development of Plate Tectonics, which provides a comprehensive understanding of Earth’s dynamic processes and continues to shape our planet today. The legacy of Wegener’s work lies in its revolutionary shift in perspective, demonstrating that Earth is not static but constantly evolving.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.