Spotting a Supercontinent: How Pangea Was Discovered

This image shows the distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the early Triassic period (approximately 252 to 247 million years ago). At this time, most of Earth’s landmasses were connected, forming the supercontinent Pangea. The present-day coastlines and tectonic boundaries of the configured continents are shown in the inset at the lower right.

Adapted from: C.R. Scotese, The University of Texas at Arlington

But how do we know that Pangea actually existed? After all, human beings evolved only a few hundred thousand years ago, so no one was around to witness this geomorphological monstrosity. How did scientists “discover” Pangea and other supercontinents of the past? Nowadays, they can study the geologic record and use radioactive dating, seismic surveys, and other technologies to construct maps of how the world looked at various points in Earth’s history. Pangea’s existence was first proposed in 1912, however, well before the invention of these tools and the development of the modern theory of plate tectonics.

German meteorologist Alfred Wegener first presented the concept of Pangea (meaning “all lands”) along with the first comprehensive theory of continental drift, the idea that Earth’s continents slowly move relative to one another, at a conference in 1912 and later in his book The Origin of Continents and Oceans (1915). Like a handful of other scientists who came before him, such as 19th-century German naturalist Alexander von Humboldt, Wegener became impressed with the similarity in the coastlines of eastern South America and western Africa and wondered whether those lands had once been joined together. Sometime around the year 1910 he began to consider whether all of Earth’s present-day continents had once formed a single large mass, or supercontinent, long ago, and had subsequently broken apart. Wegener’s presentation ran counter to the dominant paradigm of the time, which suggested that large portions of continents foundered and sank beneath the oceans over time.

Wegener pointed out that the outline, the geomorphology (rocks and landforms), and the climate belts of eastern South America were similar to those of the southwestern coast of Africa. He also argued that fossils of certain plants and animals appeared on both of these continents—and that while they were alive these organisms couldn’t have traversed the width of the South Atlantic that currently separates the two continents. So, logic suggested that South America and Africa had once been part of the same landmass. Wegener concluded that South America and Africa (as well as others) had been connected to one another, possibly through land bridges, some 250 million years ago. He also believed that Pangea had lasted through most of Earth’s history. Wegener relied on the work of Austrian geologist Eduard Suess, who (although he was a big proponent of the existence of sinking continents) first developed the concept of Gondwanaland—a supercontinent lasting from 600 million to 180 million years ago and made up of present-day Africa, South America, Australia, India, and Antarctica. Suess spotted rock formations in India that compared well in terms of age and composition with similar formations across various Southern Hemisphere continents. Wegener used Seuss’s work to support his own continental drift hypothesis and considered Gondwanaland to be the southern half of Pangea.

Despite having this geological and paleontological evidence, Wegener’s theory of continental drift was not accepted by the scientific community, because his explanation of the driving forces behind continental movement (which he said stemmed from the pulling force that created Earth’s equatorial bulge or the gravitational pull of the moon) were refuted. Wegener died in 1930, well before many of his ideas regarding Pangea and continental drift were vindicated. Other scientists, however, such as South African geologist Alexander Du Toit, continued to collect evidence in support of continental drift.  Du Toit proposed the idea of Laurasia—an ancient supercontinent in the Northern Hemisphere that included North America, Europe, and Asia (except peninsular India)—in his book Our Wandering Continents (1937).

Developments in rock and mineral dating, sonar, and geophysics ultimately vindicated Wegener. The rock formations of eastern North America, Western Europe, and northwestern Africa were later found to have a common origin, and they overlapped in time with the presence of Gondwanaland. Together, these discoveries supported the existence of Pangea. In addition, evidence supporting continental drift mounted during the 20th century, and scientists described a mechanism that seemed to explain continental movement by the 1960s, which was folded into the modern theory of plate tectonics. This mechanism was the process of mantle convection—where heated mantle from Earth’s interior rises to the surface to drive apart tectonic plates in opposite directions. Although so-called spreading centers (linear boundaries between diverging plates on the ocean floor characterized by rising magma) have been shown to exist, an explanation of how mantle convection actually works remains elusive to this day.

Modern geology has shown that Pangea did actually exist. In contrast to Wegener’s thinking, however, geologists note that other Pangea-like supercontinents likely preceded Pangea, including Rodinia (circa 1 billion years ago) and Pannotia (circa 600 million years ago). Today, Earth’s tectonic plates continue to move, and their motions are slowly bringing the continents together once again. Within the next 250 million years, Africa and the Americas will merge with Eurasia to form a supercontinent that approaches Pangean proportions. Such an episodic assembly of the world’s landmasses has been called the supercontinent cycle or, in honor of Wegener, the Wegenerian cycle.

By John P. Rafferty 

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s