The Origin of Plate Tectonics

It is remarkable to think that the theory of tectonics, the premise of physical geography, only came to fruition during the 1960’s. It was even deemed ‘pseudo science’ as early as last century. Francis Pyor wrote humorously in his book, ‘The Making of the British Landcape’ that, ‘I studied geology at A-Level, and when I compare my old text books with what is written today, I might as well be looking at another subject.’ The foundation of tectonics was a milestone in geography – that is for certain; an ‘intellectual revolution’ to Pyor. A great deal of today’s geographical knowledge owes its integrity to much of what we have learnt from plate tectonics. It is therefore important to understand how the study came about for any budding geographer.

Our understanding of early geology was fragmented in the early 20th Century. The Australian scientist, writer, and explorer, Sir Douglas Mawson, spent a large part of his career pulling past data together. Mawson took considerable interest in the Neoproterozoic period at the peak of his career. He was attempting to argue a case for the existence of a ‘Snowball Earth’ in millennia past. Joseph Kirschvink made an excellent case for this study but this is another story altogether. Mawson’s investigation orientated around the Neoproterozoic period, or pre Cambrian period (545 million years ago), regarded as the period in which multi-cellular life came to exist. Such animals include Trilobites and Archeocyathids (reef-building animals).

Mawson took to utilising the sediment prints on Earth from this period of Earth’s development, of which Mawson documented more than 20 around the world, stretching from the Artic to the Equator.  Mawson argued that the world had experienced ‘its greatest Ice-age’ at one point because traces of thin, smooth layers of sediment, indicative of the affects of melting ice, were found in every location he noted showing the extent of a possible ice-age. Mawson was using this data to primarily plead his case of a ‘Snowball Earth’, but it also alluded to the idea that the continents could have changed positions over time. The continents would have fallen into colder latitudes and subject to different conditions, imprinting characteristics of the climate onto the rock permanently, explaining why continents showed similarities in their sedimentary rock types. Mawson’s work was significant, and radical in its proposals. However the Mawson was not alone in his perception of the continents and their history.

As early as 1596, the Dutchman Abraham Ortelius, and shortly after the Briton, Francis Bacon, both spotted how easily South America could fit alongside Africa. Such subtle observations can be noticed clearly on a globe today. Charles Darwin too was intrigued with this idea, although he took greater action to explain the reason for this. He suggested that land had been grouped towards the centres near the Equator in former periods and had then split off. This was of further use to the later German Scientist, Alfred Wegener, who accelerated the thought process of plate tectonics in the early 20th century.

Wegener, between 1912 and 1915, authored the book ‘The Origin of Continents and Oceans’, in which he documented many of his global studies. One of the fundamental investigations he made on cross-continent analysis demonstrated that rocks found on one continent matched the rocks found on others. For instance, the geology of the Scottish Highlands was identical to the Appalachian Mountains in North America. Conjunctively, fossils of tropical species were found within layers of rock in the Artic. Both pieces of evidence lead Wegener to argue the concept of migrating continents, although the vital supporting evidence of a mantle, composed of slowly progressing magma, was missing from his work. Aside from this, he also proposed that around 300 million years ago, during the Paleozoic era, the continents as we know it were together, as a super-continent, called Pangaea, which was the first of its kind.

Tectonics had a basis to fall back on due to Wegener inferences which were widely accepted. His experiences and studies throughout the world showed patterns and correlation to one another. Despite this it was not until the 1960’s, when further study of the Earth’s lithosphere and mantle showed the Earth to contain a central core of Iron rich magma. The heat generated from the core sustains convection currents within the magma which is kept at a semi-liquid state, creating buoyancy for the continents above it.

In recent years, the study of plate tectonics has been invaluable to geographical predictions and mapping the Earth. In terms of security, it has aided in graphing areas most susceptible to earthquakes, based on the danger of plate margins, which has instigated greater preparation and warning for nations lying in such areas. The establishment of the Indian Ocean Tsunami Warning System in 2004 is an example of our greater intuition to work with the Earth and assess its power. The mapping out of plates on the Earth’s surface has answered questions concerning the existence of super-volcanoes below the Earth’s crust, such as LakeToba, in Indonesia, which lies on a convergent plate margin.

In essence, with our knowledge of tectonics, our ability to determine the movement and hence regulate the affects of plate activity has never been more acute. The chronology of plate movement has granted geographers the evidence to identify, with precision, the latitude of the continents and hence describe the climate and even ecosystems present on the Earth’s continents since the Neoproterozoic period. Perhaps more important to note is the hope we can find in being able to protect civilisation as we know it in the future, based on our hindsight of the past. In our study of the world, geography has not made a greater discovery.

Contributed by Bertie Bricusse

Leave a Reply

Your email address will not be published. Required fields are marked *