Soru

In 1912, German meteorologist Alfred Wegener proposed the theory of continental drift, arguing that Earth’s continents were once joined in a single landmass called Pangaea before drifting apart. To support this radical claim, Wegener constructed a multi-layered argument, sequencing distinct categories of geological and biological evidence.

Wegener began his argument with a simple, visual observation: the puzzle-like fit of continental coastlines. He pointed out that the eastern coast of South America and the western coast of Africa appeared as if they could lock together. Recognizing that coastal erosion made this fit imperfect, he refined his observation by comparing the edges of the stable continental shelves rather than the shoreline boundaries, revealing an even more precise match.

To demonstrate that this fit was not coincidental, Wegener next introduced geological evidence. He identified identical rock sequences, mountain ranges, and coal deposits on opposite sides of the Atlantic Ocean. For instance, the Appalachian mountain system of North America lined up perfectly with the Caledonian mountains of Scotland and Scandinavia. Wegener argued that these structures could only have formed continuously if the landmasses were connected.

Wegener then bolstered his theory by citing paleontological data. He pointed to fossil remains of identical species found in locations separated by vast oceans. The Mesosaurus, a freshwater reptile incapable of swimming across saltwater, was found only in eastern South America and western Africa. Wegener argued that these distributions proved the existence of land bridges or, more likely, contiguous continents, as the species could not have crossed the modern Atlantic.

Finally, Wegener incorporated paleoclimatic data, showing that ancient glacial deposits and tropical coal beds lay in regions that currently have incompatible climates. By showing that equatorial regions once experienced glaciation while northern regions were tropical, he argued that the continents had shifted relative to the equator. Although Wegener’s theory was initially rejected because he could not identify the physical mechanism driving the movement, his careful sequencing of diverse evidence laid the groundwork for modern plate tectonics.

Based on the passage, arrange the pieces of evidence Alfred Wegener uses to support his theory of continental drift in the order they are introduced to develop his argument.