Alfred Wegener, a German meteorologist, introduced his hypothesis of continental drift in 1912, challenging the prevailing scientific belief that the continents were static. Geologists widely held a theory of fixism, maintaining that the continents and ocean basins had always been positioned as they are today. Wegener proposed that Earth’s landmasses had once been connected in a single, massive supercontinent. He spent the next two decades gathering varied lines of evidence from geology, climate, and paleontology to support this claim, which overturned the established view of the planet’s history.
Framing the Continental Drift Hypothesis
Wegener’s hypothesis centered on the existence of a single supercontinent he named Pangaea, derived from the Greek words meaning “all lands.” This immense landmass began to fracture and separate approximately 200 million years ago, with the resulting fragments slowly drifting across the globe to form the modern continents. The core concept was that these vast continental blocks, composed of lighter crustal material, were moving horizontally over geological timescales. This movement explained the striking parallel between the coastlines of continents, particularly the eastern edge of South America and the western edge of Africa, which appeared to fit together like pieces of a colossal jigsaw puzzle. The fossil record provided compelling data to support the past connection of these separate continents.
Specific Fossils That Supported Pangea
The distribution of specific extinct organisms provided direct biological proof that modern continents were once merged into a southern supercontinent known as Gondwanaland, a major part of Pangaea. The fossil record showed consistent distribution patterns for four distinct species across currently separated landmasses, demonstrating that these species had once roamed freely across contiguous land.
Key Fossil Evidence
- The freshwater reptile Mesosaurus is found only in Early Permian rock formations in Southern Africa and Eastern South America. Since this small, crocodile-like reptile was adapted exclusively to freshwater, it could not have swum across the vast, saltwater Atlantic Ocean.
- The terrestrial reptile Lystrosaurus, a dominant land animal during the Early Triassic period, has fossils distributed across Antarctica, India, and South Africa.
- The land-dwelling, mammal-like reptile Cynognathus is found exclusively in Triassic-aged sediments of South America and Africa.
- The seed fern Glossopteris extended the evidence across all the southern continents—South America, Africa, India, Australia, and Antarctica. This woody plant produced seeds too large and heavy to be carried across oceans by wind or current.
The Unique Strength of Biological Evidence
While Wegener also presented evidence from matching rock strata and similar glacial deposits, the biological constraints imposed by the fossil record were particularly persuasive. The fossil evidence presented a challenge to the prevailing scientific community that was difficult to dismiss by invoking chance or alternative geological processes. Critics had to account for how multiple species of land-bound or freshwater organisms could have simultaneously colonized widely separated continents. The land-bridge theory, a popular counter-argument, suggested that temporary strips of land had once connected the continents, allowing migration before sinking beneath the sea. However, this theory failed to explain how deep-ocean basins could accommodate such massive, submerged structures or why the fossil distributions were so perfectly confined to the proposed boundaries of Pangaea.
From Hypothesis to Plate Tectonics
Despite the compelling fossil and geological data, Wegener’s hypothesis faced rejection from the geological community for decades because he lacked a plausible mechanism to explain continental movement. He incorrectly suggested that the continents plowed through the ocean floor, driven by forces like the Earth’s rotation, which physicists quickly demonstrated were far too weak. For the scientific community, evidence without a mechanism was considered insufficient to overthrow the established theory of static continents. Decades later, new oceanographic research provided the missing mechanical explanation through the discovery of seafloor spreading and subduction. Evidence from paleomagnetism, which showed symmetrical magnetic striping on the ocean floor, proved that new crust was continuously being formed at mid-ocean ridges. This understanding led to the comprehensive theory of Plate Tectonics, which ultimately vindicated Wegener’s initial ideas by defining the lithospheric plates and the driving force—mantle convection.