Lesson 1: Summary

The concept of continents fitting together like pieces of a jigsaw puzzle, particularly Africa and South America, became prominent with the publication of Alfred Wegener’s 1915 book, The Origin of Continents and Oceans. Wegener’s hypothesis of continental drift proposed that a supercontinent called Pangaea existed around 200 million years ago, which later broke apart into two large landmasses: Gondwanaland (comprising South America, Africa, the Arabian Peninsula, the Indian subcontinent, Australia, and Antarctica) and Laurasia (including North America and Eurasia). These landmasses further fragmented into the continents we know today through a process called continental drift.

Wegener’s theory was supported by several geological evidences:

1. Coastline Similarity: The coastlines of Africa and South America fit together like puzzle pieces.
2. Rock Type and Structural Similarities: Similar rock types and ages, as well as continuous mountain belts, are found on both continents.
3. Fossil Evidence: Identical fossils of organisms, like the Mesosaurus, were found on opposite sides of the Atlantic Ocean.
4. Paleoclimatic Evidence: Similar climatic data reconstructed from rock structures on different continents suggest they were once connected.

Despite the compelling evidence, Wegener’s theory faced significant resistance. His lack of a geologist’s credentials, the Northern Hemisphere bias among influential geoscientists, his underestimated timeframe for continental drift, and the absence of a mechanism to explain continental movement all contributed to its initial rejection.

The theory of plate tectonics, developed in the late 1960s, built upon Wegener’s ideas and provided the needed mechanism for continental drift. According to this theory, Earth’s lithosphere is divided into several plates that float on the semi-fluid asthenosphere. These plates, which can include both continental and oceanic crust, move at rates of a few centimeters per year and interact at plate boundaries. Plate tectonics revolutionized geology by explaining the movement and deformation of Earth’s outer layers, thereby predicting geological events like earthquakes and volcanic eruptions and providing a comprehensive framework for understanding Earth’s geological features and processes.

Plate tectonics has shown that Earth’s surface is in constant motion, influencing climate change and the environment in which life evolves. The theory is now universally accepted and forms the basis for much of modern geology.