Drift
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The theory of continental drift posits that the continents have slowly moved across the Earth's surface over a vast period of time, leading to their apparent "drift" across the ocean bed.
The notion of continental drift was first proposed in 1596 by Dutch cartographer and geographer Abraham Ortelius (1). In addition to creating the first modern atlas, Ortelius was the first person in history to notice how neatly the coastlines of the Americas and Europe-Africa joined together. He then boldly suggested the Americas had been "torn away from Europe and Africa...by earthquakes and floods." Although Ortelius had the right idea, he did not provide a plausible mechanism other than alluding to earthquakes and floods, nor did he provide evidence to support his claim, and so his observation remained nothing but an interesting conjecture for quite some time. |
Abraham Ortelius, first person to propose the notion of continental drift. |
Several centuries later, in 1906, Austrian alpinist and geologist Otto Ampferer put forward his theory of undercurrent (2). Prior to Ampferer's theory, the prevailing perception was that magma, which is the molten material beneath the Earth's crust, was unmoving or static. By contrast, the theory of undercurrent stated that magma constantly moved or flowed, which in turn created a sort of current underneath the Earth's crust, leading to the formation of high mountains and ocean basins. Ampferer's theory of undercurrent put forward a plausible mechanism for continental drift, but again, evidence was still lacking.
Less than a decade later, in 1912, German meteorologist Alfred Wegener took Ampferer's theory a step further when he formulated a more specific theory of continental drift (3). By now, a number of other scientists had also caught on to the idea, but Wegener was the first person to pointedly refer to the continents as "drifting." Extending the implications of the idea further, he proposed that the continents had once formed a single, giant landmass called Pangaea before they broke apart and drifted into their current locations. However, Wegener's theory of continental drift continued to be rejected for decades, particularly since he was not a geologist, remained vague on mechanism, and - like his predecessors - showed little in the way of evidence to support his theory. |
Alfred Wegener, first person to outline a specific theory of continental drift. |
From the 1920s to 1950s, English geologist Arthur Holmes (and others) championed the continental drift theory (4). Holmes' unique contribution was that he was the first person to propose a more complete, fleshed-out mechanism for continental drift called mantle convection, which postulated the existence of massive continental plates beneath the sea that were driven in differented directions by the flowing currents of magma beneath them. By the 1950s, studies of magnetization patterns across the Earth's seabed were providing evidence that strongly supported mantle convection as the fundamental mechanism underlying continental drift.
Currently, the theory of continental drift has morphed into a modern, well-defined science called plate tectonics (5). Plate tectonics states that the Earth's crust is broken into several major plates and a number of smaller ones. The plates move anywhere from 0 to 10 cm per year relative to each other. Depending on how they move with respect to each other, the edges of the plates lead to earthquakes, volcanoes, mountain-building, and oceanic trench formation.
The implications of plate tectonics are fascinating, for they imply that the Earth's continents have drifted across the ocean bed for billions of years.
Supercontinents
Occasionally, the continents of the world have come together to form a supercontinent, which is typically defined as a conjoined landmass encompassing at least 75% of the Earth's available continental crust at any time (6). By this definition, there have been three major supercontinents during Earth's history.
The first and oldest supercontinent was Columbia (also known as Nuna or Hudsonland), which existed 2.5-1.5 billion years ago (6,7). Columbia was nearly 13,000 kilometers at its broadest part. This supercontinent would have been devoid of life, which would have existed only in the sea as either single-celled organisms, or the very earliest of Earth's multicellular lifeforms.
Next in line was Rodinia, which existed 1.1-0.7 billion years ago (6,8). Rodinia formed from the accretion of all the continental fragments created by the breakup of Columbia. It was probably cloaked by many large glaciers. Rodinia was also barren of life, although multicellular lifeforms thrived in the sea.
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The supercontinent of Pangaea, with modern political borders outlined (10). |
Today, there is no supercontinent in existence - the closest thing we have to one is the conjoined landmass encompassing Asia, Africa, and Europe, which accounts for only 57% of the Earth's continental crust.
Superoceans
As impressive as the supercontinents were, the oceans around them were even more colossal - in many ways, the yin to the yang. For of course, whenever their was a supercontinent there was also a superocean surrounding it, typically defined as any ocean larger than the current Pacific Ocean (11).
The superocean surrounding Pangea was called Panthalassa (meaning "all sea" in ancient Greek), which occupied almost 70% of the Earth's entire surface. Due to mantle convection and the continuous subduction of the ocean floor underneath the continental plates, the actual ocean floor underlying Panthalassa has now completely disappeared. The current Pacific Ocean is the direct descendant of Panthalassa, a smaller remnant of this once mighty sea. Panthalassa would have held an abundant variety of lifeforms including corals, molluscs, sharks, and the earliest species of bony fish.
The prehistoric superocean Panthalassa, yin to the yang (12).
Cleary, nothing is truly static...not our theories about the world, and not even the continents and oceans. Given this realization, any attempt to maintain a rigid view of the world - or even a long-term state of stability in one's own life - is obviously doomed from the outset. Even if that world-view seems perfect, or that person appear to have successfully mastered life...perhaps, especially if that world-view seems perfect, or that person appears to have successfully mastered life. The reality is that even the mighty continents and oceans undergo cycles of being shoved together and torn apart - this is entirely normal and natural, and the same applies to people. It is a process that should not be feared, but embraced.
Permanence is the illusion, impermanence the rule...and truth lies in drift.
Solace.
References:
(1) https://en.wikipedia.org/wiki/Abraham_Ortelius.
(2) Dullo and Pfaffl. 2019. The theory of undercurrent from the Austrian alpine geologist Otto Ampferer (1875–1947): first conceptual ideas on the way to plate tectonics. Can J Earth Sci 56(11), 1095-1100.
(3) https://en.wikipedia.org/wiki/Alfred_Wegener.
(4)https://en.wikipedia.org/wiki/Arthur_Holmes.
(5) https://en.wikipedia.org/wiki/Plate_tectonics.
(6) Mitchell et al. 2021. The supercontinent cycle. Nat Rev Earth Environ 2, 358-374.
(7) https://en.wikipedia.org/wiki/Columbia_(supercontinent).
(8) https://en.wikipedia.org/wiki/Rodinia.
(9) https://en.wikipedia.org/wiki/Pangaea.
(10) https://randommization.com/2013/06/06/map-of-the-pangea-with-modern-political-borders/.
(11) https://en.wikipedia.org/wiki/Superocean.
(12) https://geografia.laguia2000.com/general/pantalasa.
