The Fascinating Phenomenon of “Supercontinent Cycles”

 

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We all are familiar with the legend of Atlantis. A mythical continent which was home to a highly advanced and prosperous civilisation. I call it mythical because there is no proof that it ever existed. The legend was arguably authored by Plato around 360 BC. He named it the “Island of Atlas”. He created the fictional Atlantis Civilisation as a sort of literary version of Athens.

Plato’s Atlantis parable was supposed to underscore his philosophical and moral postulations. According to Charles Orser, the curator of history at the New York State Museum, there have been unproven speculations of the continent’s location whose people were “half human and half gods.” Plato had imagined the Atlantis civilisation as the one that fell from the high pedestal of virtue and spiritualism to the depths of moral bankruptcy. This angered the gods and destroyed the continent with a series of volcanic eruptions and earthquakes, consequently sinking Atlantis into the oceanic depths.

True or not, the legend does underline the changes that our planet has been undergoing since countless millennia. Let us be clear that the planet, as we know it today, wasn’t always so. There have been transformations that are both scary and fascinating. Scary because entire regions and continents have disappeared into the oceans. Were those continents populated? Were there civilisations of which we know nothing, or very little, today, and can only indulge in conjectures? Fascinating because new continents have emerged from the oceanic depths, and are populated by an almost infinite range of flora and fauna, not to mention a wide variety of human ethnicities.

The submergence of existing continents and emergence of new ones have been part of continuous processes, described as “Supercontinent Cycles” which have been sometimes subtle and sometime not so subtle. This phenomenon is the result of tectonic movements. Now what are these tectonic movements? 

The earth’s outermost layer is called the crust, which is divided into several large plates called tectonic plates. The plates  are massive, irregularly shaped solid rocks, around 100 kilometres thick, consisting of two principal types of material: the oceanic crust and the continental crust. The earth’s rigid outer layer, or lithosphere, is broken into tectonic plates. Although there are several major and minor tectonic plates, seven major ones comprise African Plate, Antarctic Plate, Eurasian Plate, Indo-Australian Plate, Australian Plate, North American Plate and Pacific Plate. When these plates move, earthquakes happen. The movements of tectonic plates are caused by convection currents, ridge push and slab pull.

The convection currents are warm currents that carry and drive the  lithosphere’s tectonic plates in the conveyor belt fashion. The ridge push occurs when gravity pulls newly formed plates from atop oceanic ridges. The slab pull occurs when older plates start sinking. As the plates age, they become colder, denser and heavier. While sinking, they pull the warmer plates with them.

Like the mythical Atlantis, several real continents are presently submerged in oceans. We shall discuss some of these here.

Described as a supercontinent, the Gondwanaland was the largest and most ancient of the landmasses. It existed about 600 million years ago and covered one-fifth of the earth’s surface. It began fragmenting about 180 million years ago. During the final stages of its breakup about 23 million years ago, the Antarctica separated from South America and Australia. 

Pangea was another supercontinent that was formed from the parts of Gondwanaland, Siberia and Euramerica about 335 million years ago. It began to break apart about 200 million years ago.

Zealandia is the latest submerged continent to be discovered. The story of its discovery is quite interesting. A Dutch sailor named Abel Tasman was the first to hint at Zealandia’s existence in 1642. But he was not taken seriously. Or, perhaps, there were not enough scientific resources and skills to verify his claims. However, during the 1990s, scientists began to seriously study the possibility of Zealandia’s existence. In 1995, Bruce Luyendyk, an American geophysicist, discovered this continent while he was studying Gondwana. Originally a part of Gondwana, Zealandia is almost entirely submerged, with only 6% of its landmass above the Pacific Ocean’s surface. According to a BBC report, Zealandia is 4.9 million square kilometres in size.

There are several other continents that remain submerged. Among these, the most notable are:

1. Beringia, which connected Asia and North America during the  last Ice Age. It was bounded on the west by Russia’s Lena River, on the east by Canada’s Mackenzie River, on the north by the Chukchi Sea and on the south by the Kamchatka Peninsula. 
2. Doggerland connected Great Britain to the mainland Europe during the last Ice Age. It was home to the Mesolithic people, who were hunters-gatherers. The area was a series of gently sloping hills, heavily wooded valleys, marshlands, lagoons and swamps. Around 8200 years ago, floods and tsunamis destroyed Doggerland.
3. Kerguelen Plateau is a submerged volcanic plateau in the southern Indian Ocean. Located about 3000 kilometres southwest of Australia, it rises 2000 metres above the sea level, but most of it is about 3000 metres below the sea level. Its area is about 1.3 million square kilometres.
4. Mauritia was a microcontinent that was once a part of Madagascar and India. Today, its fragments include the Lakshadweep-Maldives-Chagos Ridge, the Nazareth Bank, the Hawkins Bank and Mauritius, etc. This microcontinent extends from Seychelles to Mauritius. 
5. The Sahul continent once connected Australia, Tasmania, and New Guinea during the last Ice Age. Its area comprised about 10.6 million square kilometres. Humans came to Sahul about 60,000 years ago, from where they spread throughout Oceania. When global temperatures increased after the last Ice Age, sea levels rose and flooded the land bridge. This resulted the separating of the Australian landmass from Tasmania and New Guinea. It was home to unique fauna that evolved independently from the rest of the world. These included a range of burrowers, scavengers, predators and marsupials. Marsupials are the species that are born incomplete and are carried in their mother’s pouch in their nascent stage; kangaroos for example.
6. The Sundaland continent connected Southeast Asia to the Malay Peninsula and Indonesian islands like Borneo, Java and Sumatra, during the last Ice Age. It was about 10.6 million square kilometres in size. It included the Java Sea, the Gulf of Thailand and the South China Sea.

The history of emergence and submergence of landmasses is fascinating, indeed. A recent international study led by scientists from India, Australia and South Africa reveals that the Earth’s first continents, also called “cratons”, may have emerged from the ocean around 3.2 billion years ago. Another study shows that about 2.7 billion years ago, huge landmasses emerged from the oceans that were exposed to weathering and erosion by the sun, wind and rain. 

And, finally, a prediction. The American geologist Christopher Scotese hypothesised in November 1982 that, in about 250 million years, a new supercontinent, Pangaea Proxima is expected to form at the equator as the Atlantic Ocean shrinks and a merged Afro-Eurasian continent crashes into the Americas. This would be consistent with the ‘Supercontinent Cycle”, claimed Christopher Scotese. 

I am sure you find the phenomenon of submerged and emerging contents, aka ‘Supercontinent Cycles”  as fascinating as I do.