Alfred Wegener, a German meteorologist and geophysicist, introduced the revolutionary concept of Continental Drift in the early 20th century. His theory challenged the prevailing view that continents were static landmasses, proposing instead that they had moved across the Earth’s surface over geological time. This idea suggested that continents were once united in a single supercontinent, which he named Pangaea, meaning “all lands.” Wegener gathered a variety of empirical observations to support his hypothesis, laying the groundwork for what would eventually become the modern theory of plate tectonics.
The Jigsaw Puzzle Fit of Continents
One of the most apparent pieces of evidence supporting Continental Drift was the resemblance in the shapes of continental coastlines. Wegener observed how the western coast of Africa and the eastern coast of South America appeared to fit together like a giant jigsaw puzzle. When considering the continental shelves, which are the submerged edges of the continents, the fit becomes even more precise, suggesting these landmasses were once connected. This alignment provided a strong visual argument for their past connection.
Unearthing Ancient Life: Fossil Evidence
Wegener strengthened his argument by examining the distribution of identical fossil species found on continents now separated by oceans. He highlighted the freshwater reptile Mesosaurus, whose fossils are found exclusively in southern Africa and eastern South America. This aquatic reptile, unlikely to have traversed a large saltwater ocean, indicated that these two continents were once connected. The ancient seed fern Glossopteris also provided evidence, with its fossils discovered across South America, Africa, India, Australia, and Antarctica. The wide distribution of this non-marine plant supported the idea that these regions were once part of a unified landmass, Gondwana.
Connecting Continents Through Rocks and Mountains
Wegener also presented geological evidence, noting similarities in rock types and mountain ranges across oceans. Identical rocks of the same age are found on both sides of the Atlantic Ocean, suggesting they formed together before the land moved apart. The Appalachian Mountains in eastern North America and the Caledonian Mountains in Greenland, the British Isles, and Scandinavia provide a prime example. These mountain belts exhibit similar rock types, structures, and ages, implying they were once part of a single, continuous chain formed when these continents were joined.
Clues from Ancient Climates
Wegener’s theory also drew support from ancient climates, or paleoclimates. He found signs of past glacial activity, such as glacial deposits, in regions now tropical or subtropical, including South America, Africa, India, and Australia. This presence of ancient ice sheets in warm climates was puzzling unless these continents had been closer to the poles. Conversely, ancient tropical swamps, indicated by coal deposits, were found in regions now in polar or temperate zones, like Europe and Siberia. These climatic indicators could only be reconciled if the continents had moved from different climatic zones over geological timescales.