AKA: The movement of continents is caused by the gradual expansion of the Earth.
Theory born: 1834
Parent(s): Charles Darwin, Ott Christoph Hilgenberg, Samuel Warren Carey
It had long been noted that there was something strange about the shape of Earth's continents. In 1620, the natural philosopher Francis Bacon noted that the shapes of the coasts of South America and Africa seemed complimentary - "more than a curiosity" - but he was unable to suggest any reason why it might be so. Others suggested that they were forced apart by the creation of the Atlantic Ocean when the "lost city of Atlantis" was destroyed or that the appearance of the surface of the Earth was because of a series of catastrophic events inflicted by God in the distant past.
In 1834, during the famous voyage of the HMS Beagle, Charles Darwin arrived in Patagonia and noted the stepped plains and raised beaches.
Darwin concluded that some huge force from within the Earth had acted equally throughout the region (and, indeed, the whole continent, which lead him to hypothesise "the gradual expansion of some central mass" [of the earth] "acting by intervals on the outer crust". Although he did not pursue this theory much further, others would.
One of the theory's more famous early 20th century proponents was the German geophysicist Ott Christoph Hilgenberg. In the 1930s, he began publishing work that explained his idea that the Earth had been significantly smaller in the past. This could be clearly seen in his scale models of the continents: if the Earth had always been this size, the continents could all fit together well-enough but with large gaps in places. However, if the Earth was shrunk by approximately 60%, the continents fit together more or less perfectly. Only vague mechanisms were suggested as to how this expansion was occurring.
However, cracks had already begun to appear in this theory (so to speak). In 1912, meteorologist and geophysicist Alfred Wegener had published his theory of 'continental drift'.
Alfred Wegener: b. 1880, d. 1930
He had analysed rock structures and fossils of plants and animals and found them to be the same in the coastal regions of Africa and South America that bordered the South Atlantic. He concluded that the two regions had been geologically connected and that some mechanism (he suggested perhaps the Earth's rotation) had caused the continents to move apart. He then went on to suggest that all continents had reached their current positions by ploughing through the crust like an icebreaker and that, in the distant past, they had all been joined together in a supercontinent that he named Pangea, surrounded by a massive body of water - the Panthalassa. He even went to far as to outline ocean-spreading as a concept: that "the Mid-Atlantic Ridge ... zone in which the floor of the Atlantic, as it keeps spreading, is continuously tearing open and making space for fresh, relatively fluid and hot [molten rock rising] from depth." This is actually what happens in reality, but he did not pursue the idea any further.
The super-continent Pangea
His theories were not well-received by contemporary scientists. Many took issue with the 'icebreaker' mechanism, pointing out that the ocean floor was far too tough for this to occur. Others misunderstood his ideas about the continents fitting together (possibly due to a poor German-to-English translation of his paper) and thought that he meant that the exact coastlines of continents fit together (thus ignoring all coastal erosion in changing their shapes), rather than what he actually wrote: that the coasts 200m underwater - at the level of continental shelves - fit together. Finally, there was a good dose of scientific snobbery: Wegener was a meteorologist primarily and therefore could not possibly contribute anything to the geological sciences. Without wider support, the theory remained on the fringes.
In the 1950s, an Australian geologist named Samuel Warren Carey began to champion Wegener's work. He had performed countless simulations on the shape of continents and agreed with Wegener that at some point they had all fit together as Pangea. However, he had also noticed that shrinking the Earth by 60% led to a perfect fit and postulated that Wegener's continental drift was caused by the expansion of the Earth. However, again, a mechanism behind the expansion of the Earth could not be identified and Carey suggested that a new law of physics would be discovered to validate his work.
Theory death: 1960s
Cause of theory's death: Incompatible with observed data and the theory of plate tectonics.
While Carey was publishing this work, a serious study of magnetic stripes in the seafloor was underway. These magnetic stripes had been formed when rock had been molten and the magnetic minerals in the molten rock had aligned with the Earth's magnetic field. When the Earth's magnetic field periodically reversed, it led to the new rock's magnetic minerals being orientated in the opposite direction (leading to 'stripes').
These rocks helped to prove Wegener's continental drift theory correct. But what of Carey's theory that this was driven by the expansion of the Earth? Further study showed that while new seafloor was being created at some plate boundaries, it was being destroyed at others by being forced under other plates (through a process called subduction). If the amount of crust on Earth was remaining constant, there was no need for an 'expanding Earth' theory to account for 'extra' crust created through seafloor spreading.
More recent modelling using data from the magnetic stripes then suggested that the Earth's radius 400 million years ago was 102 ± 2.8 percent of today's radius - not significantly larger. Studies of the Moon's orbit around the Earth and of the Moon's impact on tides and the formation of sedimentary rocks has suggested that the Earth's radius has not significantly changed over 680 million years.
With no evidence supporting it, it was now the turn of expanding Earth to lurk on the fringes of scientific discourse.
Attributions
Pangea image: Kieff, Wiki Commons
Raised beach photograph: Tony Atkin, Wiki Commons
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