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 500 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 piece of land. This was the early version Gondwana, stretching from the Equator almost to the south pole. 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.

More continents collided with this early Gondwana over time forming 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 millions of years later, 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.

Pangea’s breaking-up stages.
Image credits U.S. Geological Service.

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 southernmost 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.

South America and Africa with the approximate location of their Mesoproterozoic (older than 1.3 Ga) cratons (old and stable parts of the crust.)
Image credits Woudloper / Wikimedia.

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 bee-line towards Eurasia — the collision between the two 50 million years ago 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.

Today’s tectonic plates. Red arrows indicate primary direction of movement.
Image credits U.S. Geological Survey.

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 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 criticised 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, and had no known way to reliably re-create 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 floras and faunas found exclusively on southern continents, especially the fern species Glossopteris. His theory gained traction with scientists from the southern hemisphere but was still widely criticised 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 create new oceanic plate, pushing continents apart.

This cemented the theory of tectonic plates, and furthermore helped us understand how these huge landmasses moved in the pases – including how Gondwana came to be and ultimately broke up.

How magnetic stripes form on the sea floor.
Image credits Chmee2 / Wikimedia.

Gone-dwana?

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 Gonwdana and the supercontinents before it function 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.

But considering the timeframes geology works with, we’re probably not going to be around any longer to when it happens.

 

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