Tectonics and Landforms

Looking for the evidence

If the continents were in one piece at some time in the past, we should find similar fossils and rocks on both continents which is precisely what Wegener discovered. By studying the geologic record, the fossil record, and climatic record, he found remarkable similarities between Africa and South America.

Figure 15.5 Fossil Glossopteris leaf, Ellsworth Land, Antarctica
Click image to enlarge
(Photo Credit USGS DDS21)

Fossils of the same species of plants and animals were found in similar geologic formations in different parts of the world, most notably South America, Africa, and India. For example, fossils of the Glossopteris, an ancient fern, are found in South America, Africa, Antarctica, India, and Australia. It was hypothesized that such a distribution could only come about if the continents were all part of the one super-continent.

Examining the stratigraphy (vertical sequences) of the rock record, Wegener could point to further evidence for Pangea and continental drift. Wegener noted that the rock sequences in South America, Africa, India, and Australia are very similar. Wegener showed that the same three bottoms layers occurred on each of the continents. The bottom layer, called tillite, was thought to be of glacial origin. The middle layer composed of coal beds, shale and sandstone contained Glossopteris fossils, as did the bottom tillite layer. The top most and youngest layer is lava flows. Such a strong similarity in the rock record of these localities, now separated by great geographic distance, lent credence to Wegener's notion of continental drift.

The occurrence of glacial features (Figure 15.7) in the geologic record of South America, Africa, India ,and Australia provides further evidence for the notion of continental drift. Glaciers affected all or part of these continents at the same time in Earth history.