Millions of years ago, the Earth looked vastly different from today. The continents were arranged in a way that would be unfamiliar to us, and one landmass dominated the others: Gondwana.
Gondwana used to be a supercontinent, from around 550 million years ago to approximately 180 million years ago, alongside Laurasia. Gondwana incorporated present-day South America, Africa, Arabia, Madagascar, India, Australia, and Antarctica.
But what happened to Gondwana, and what can it tell us about our planet's history?
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Gondwana: The supercontinent that once was
The Earth is a planet alive.
That shouldn't surprise anyone -- after all, our planet is bustling with life on the surface. But it goes deeper than that, literally. The atmosphere, the magnetic field that prevents solar radiation from frying us alive, the terrain on which we live -- these are all the product of lively processes taking place under the surface.
For most people, the world around us seems like a very stable place. Its shape seems, pardon the pun, set in stone. But the continents we know today are only a temporary arrangement, and they looked very different in Earth's earlier history.
Be patient enough, and you'll see the earth itself spring to life -- it moves, breaking apart or coming together all over the planet. This is the story of the last in a breed of geological titans, a supercontinent we named Gondwana.
A different Earth
Some 540 million years ago, during the late Ediacaran period, tectonic motions brought today's Africa, South America, Australia, Antarctica, India, the Arabian Peninsula and Madagascar into a single, massive landmass. This was the early version Gondwana, stretching from the Equator almost to the south pole, covering nearly one-third of the Earth's surface. Its climate was mild, however, as the world was a warmer place back then. Multicellular organisms had developed by this time, but they were primitive. The few fossils we've found from this period show a biota consisting of segmented worms, round creatures resembling modern jellyfish, and frond-like organisms.
The formation of Gondwana was a gradual process that took millions of years. The continental plates that would make up Gondwana slowly collided and merged, pushed together by powerful tectonic forces. As they did, they formed towering mountain ranges, such as the Appalachian Mountains in North America and the Hercynian Mountains in Europe.
"In geology, the name Gondwana was introduced by H. B. Medlicott in 1872, in a manuscript report on the ancient kingdom of Dravidian Gonds in Central India," explains Subhrangsu K. Acharyya from the Geological Survey of India. "The Gondwana supercontinent, or Gondwanaland, has been subdivided into two parts, East and West, which have contrasting histories. The Indian subcontinent is a fragment of East Gondwana."
More continents collided with this early Gondwana over time to form Pangaea, the "whole Earth," roughly 300 million years ago. It was immense by any stretch of the imagination, all of the planet's landmass was fused into one block dominating the southern hemisphere, surrounded by the biggest ocean in history. Then, 20 to 70 million years later, during the Jurassic, magma plumes from the Earth's core started burning through the crust like a blowtorch, creating a rift between what we know today as Africa, South America, and North America.
"The Mesozoic paleoclimates and tectonic conditions in the Gondwana supercontinent allowed the formation of ancient landscape systems in Africa, particularly in Southern Africa, but also in India, South America, Antarctica and Australia," write geologists Jorge Rabassa and Cliff Ollier.
Convection cells associated with these plumes widened the fissure into a fully-fledged Tethys ocean, separating a northern supercontinent called Laurasia -- today's North America, Europe, and Asia -- from a southern one, our fully formed Gondwana. It has lost some of its original bits to Laurasia -- such as Florida and parts of Georgia -- but still contains all the landmasses we see today in the southern hemisphere. We're now in the Jurassic period. Dinosaurs are roaming about, most of the world is covered in lush rainforests, and the last supercontinents are poised to break up.
It's not you, it's tectonics
The break-up didn't happen at once, however. Gondwana fragmented in stages. Sometime between 170 million and 180 million years ago, modern Africa and South America began breaking apart from the rest of Gondwana. They stayed fused for about 30 to 40 million years until the South Atlantic Rift broke them up, opening the ocean (with the same name) between them.
That's why South America's eastern coast and Africa's western coast look like they'd fit together snugly -- at one point, they actually did.
At about the same time as the South Atlantic Rift was opening up, the easternmost part of the continent, Madagascar and India, split from the rest, opening the central Indian Ocean. The two stayed fused together until the Late Cretaceous period, after which India made a beeline for Eurasia -- 50 million years ago, the collision between the two was so violent it raised the Himalayas.
At this point basically all that's left of former Gondwana is Australia and Antarctica -- too little to be counted as a supercontinent. They did stay fused together until around 45 million years ago, though. After that, Antarctica moved south and froze over (due to a combination of the climate cooling down and shifting ocean currents around the new landmasses) and Australia went adrift towards the north, colliding with southern Asia. The collision is still taking place today, as the Australian plate is advancing north at a rate of about 3 centimeters (1.2 inches) a year.
We still don't know exactly what caused the continent to break apart. One theory holds that hot spots formed beneath it, creating rifts that broke the supercontinent apart. In 2008, however, University of London researchers suggested that Gondwana instead split into two tectonic plates, which then were then further fragmented.
How we figured all of this out
The uncanny resemblance between the shape of western Africa and eastern South America was first officially noted by Sir Francis Bacon in 1620 as accurate maps of the two continents became available. In 1912, Alfred Wegener, a German meteorologist, proposed that the two continents formed a single body at one point -- in fact, he was the first to envision the great supercontinent Pangaea. However, geologists at the time strongly criticized his theory, citing his lack of formal training in the field. Geologists then couldn't believe that something as huge as a continent could move; they simply lacked knowledge of a system that would explain how this could happen; they had no known way to reliably recreate the movements.
Alexander Du Toit, a South African geologist, further elaborated on the theory in his 1937 book Our Wandering Continents. Seeing the opposition Wegener's theory encountered, he carefully amassed evidence of the two continents' past link -- the occurrence of glacial deposits (or tillites) and rock strata on both sides of the Atlantic, as well as similar fossil flora and fauna found exclusively on southern continents, especially the fern species Glossopteris. His theory gained traction with scientists from the southern hemisphere but was still widely criticized by geologists in the northern hemisphere. They envisioned land bridges spanning from continent to continent to explain how one species could be found on both sides of an ocean, even to the point where these bridges would circle whole continents.
However, the theory of plate tectonics became widely embraced by the 1960s when the Vine–Matthews–Morley hypothesis was formed following paleomagnetism (or fossil magnetism) measurements of the ocean's floor. These measurements recorded the magnetic properties stored in ocean-bottom rocks as they formed over time, proving that rift areas add new material to oceanic plates, pushing continents apart.
This cemented the theory of plate tectonics and furthermore helped us understand how these immense landmasses moved in the past -- including how Gondwana came to be and ultimately broke up. Essentially, Gondwana was broken up by the same tectonic forces that had previously brought Gondwana together in the first place.
Life in Gondwana
Gondwana was home to a diverse array of plant and animal life, much of which was unlike anything found on Earth today. Scientists have uncovered fossils of ancient reptiles, amphibians, and even early mammal-like creatures that lived on the supercontinent. The discovery of these fossils has provided valuable insight into the evolution of life on Earth.
"The general idea of Gondwana landscapes is closely related to the concept of long-term landscape evolution. This implies that landscapes may be developed along extreme long time periods, provided that warm/wet climates and tectonic stability are given," add Gondwana experts Rabassa and Ollier.
"However, it should be taken into consideration that a long-term landscape may also evolve under arid conditions; it just happens that the real history for most of these landscapes was warm-humid."
Unsurprisingly for this warm-humid environment, one of the most significant finds from Gondwana is the discovery of ancient, tree-like ferns. These ferns, known as glossopterids, were incredibly large and are thought to have been one of the dominant forms of vegetation on the supercontinent. Scientists believe that they may have played an important role in the formation of coal deposits, which are now a major source of energy around the world.
The breakup of Gondwana also had a profound effect on the distribution of species around the world. As the continents separated, the plants and animals that lived on them were also separated. This led to the development of unique ecosystems and the evolution of distinct species on each continent.
Gondwana is the last of the supercontinents the world has seen -- so far. Plates are being formed and consumed today, just as they have been since the Earth's crust cooled down to a solid. The same tectonic processes that made and shattered Gondwana and the supercontinents before it functions just the same, powered by the huge quantity of heat trapped in the depths of the Earth. They will keep on mashing continents together, so it's almost guaranteed that a new supercontinent will form in the future. The very distant future, that is -- millions of years from now.
Today, the remains of Gondwana are scattered around the globe, but its legacy lives on. The mountains, deserts, and other landscapes that were formed during the supercontinent's existence can still be found on the continents that it once made up.
The fossils of the ancient creatures that lived on Gondwana give us a glimpse into the distant past and provide valuable insights into the evolution of life on Earth. And the coal deposits formed from the ancient glossopterids continue to be a major source of energy around the world.
Overall, Gondwana was a critical step in the Earth's history, its study can provide an understanding of plate tectonics, climate, and life evolution and how they shaped our world. Gondwana's story is still unfolding, it's a reminder of how much more there is to learn about our planet and its history.