Plate Tectonics

Early Speculation

The first recorded suggestions of a dynamic and changing Earth were offered by 16th-century philosophers and geographers, who noted the congruence between the Atlantic coastlines of Africa and South America. In 1596 the geographer Abraham Ortelius argued that the Americas were once conjoined with Europe and Asia, but later “torn away” by earthquakes and other catastrophes. In recent years, historians of science have discovered nascent hints of plate tectonics in the writings of Francis Bacon, Scottish philosopher Thomas Dick, noted French scientist Comte de Buffon, German explorer Alexander von Humboldt, and Benjamin Franklin. However, it wasn't until the early 20th century that scientists began to assemble strong evidence that the surface of the earth has changed over time, as well as a coherent hypothesis to explain how. Much of this data set was articulated by Alfred Lothar Wegener, a German meteorologist who assembled widely divergent lines of evidence into an understandable theory of continental motion.

Wegener and Continental Drift

Like the early geographers before him, Wegener was intrigued by the closely matching Atlantic coasts of South America and Africa. After reading a paper describing similar Paleozoic fossils from these two continents, Wegener launched a massive literature search in the hopes of finding additional data to support the concept of continental drift. The data he uncovered were varied and wide ranging. Not only did the coastlines of South America and Africa match, but so too did the coasts of Newfoundland, England, parts of Greenland, and Scandinavia, especially when the outlines of the continental shelf were taken into account. Additionally, Wegener discovered that South America, Africa, India, Australia, and Antarctica shared a suite of unique Mesozoic fossils, including a tropical plant flora characterized by the fern Glossopteris and a reptile fauna that included the tusked, piglike Lystrosaurus. Modern animals do not range across all continents, because it is often impossible to disperse across oceans and other barriers. This suggested to Wegener that these continents were linked during the Mesozoic era (225–65 million years ago), and have since moved to their present, widely divergent positions. Furthermore, the presence of tropical fern fossils in Antarctica makes no sense if the continent has always occupied a polar position.

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