We explain what continental drift is, who devised the theory and what evidence was taken into account. Also, what is the theory of plate tectonics.
What is continental drift?
Continental drift is a theory that postulates that continents move. This is a geological theory proposed in 1912 by the German geophysicist and meteorologist Alfred Wegener (1880-1930).
The theory of continental drift states that at some point in geological time The continents were united into a supercontinent called Pangea. (from Greek bread“everything”, and gea“earth”), and that approximately 200 million years ago they would have begun to separate.
Wegener supported his theory on evidence linked to the shape of the continents and with fossil and geological remains found. Demonstrating the existence of Pangea was for him the possibility of verifying the movement of the continents, since they are currently in different positions compared to that time.
At the time, the theory was received with a lot of skepticism by the scientific community, since at that time the idea that the position of the continents was fixed was widely accepted. Furthermore, Wegener could not explain what force was capable of moving these large continental masses, so his proposal was rejected by the majority of scientists.
The following years of his life and until his death, Wegener continued to research continental drift and possible explanations for the movement of the continents.
Frequently asked questions
What does the theory of continental drift propose?
The theory of continental drift proposes that the continents move and that 200 million years ago they were united into a supercontinent called Pangea.
Who developed the theory of continental drift?
The theory of continental drift was proposed by the German scientist Alfred Wegener in the book The origin of the continents and oceanspublished in 1912.
What are the four pieces of evidence for continental drift?
The evidence of continental drift is the convergence between the limits of the continents; the coincidence in the origin and rock components of mountains and mountain ranges located on different continents; the distribution of the fossils found; and the existence of glacial valleys in currently warm areas.
Evidence of continental drift
There are four main pieces of evidence for the theory of continental drift:
- Shapes of the continents. The coincidence between the limits of the different continents, especially Africa and America, which seemed to fit together, was for Wegener fundamental evidence that they were initially united in the supercontinent called Pangea.
- rock components. The coincidence in the geological origin and rock components of mountains and mountain ranges located on different continents demonstrated that these mountain ranges had at some point been united, and that due to the separation of Pangea they would have fractured and moved apart.
- Fossils. The presence of fossils of plants and animals on distant continents, such as the mesosaurus and glossopteris found in Africa and America, demonstrated the existence of Pangea. Wegener considered that these animals and plants had lived in the same region and that, if today the fossils were dispersed on different continents, it was due to the separation of Pangea.
- glacial valleys. Glacial valleys occur in cold regions, where low temperatures allow the formation of glaciers. For Wegener, the existence of glacial valleys in warm areas was explained by the movement of the continents: initially they were in cold areas and, due to continental drift, they moved towards warmer regions. In that movement the glaciers melted, but the glacial valleys remained as geological evidence.
Stages of continental drift
Pangea was not the first supercontinent. Before there were others, which separated into pieces and formed other supercontinents successively until they reached the current continents. This process can be broadly summarized in the following stages:
- About 1.1 billion years ago the supercontinent of Rodinia was formed the first large block of land from which all the continents come. The possibility that there were some previous supercontinents (such as Ur or Columbia) is not ruled out, but there is not enough evidence to confirm it.
- About 750 million years ago Rodinia began to fragment and from its remains a new supercontinent would emerge.
- about 600 million years ago Pannotia was completed a second supercontinent.
- About 540 million years ago Pannotia fragmented into two smaller supercontinents: Gondwana to the south, made up of what are now Africa, South America, India, Oceania, Madagascar and Antarctica; and another block to the north, made up of Asia, Europe and North America. Between them, a new ocean was formed: Proto-Tethys.
- about 500 million years ago three new continents were formed: Laurentia, Siberia and Baltica which in turn led to the creation of two new oceans: Iapetus and Khanty.
- About 485 million years ago, in the Ordovician period, a microcontinent separated from Gondwana: Avalonia corresponding to the current United States, Nova Scotia and England, and began its journey north to join Laurentia. Baltica, Laurentia and Avalonia collided to form Euramerica.
- About 440 million years ago Gondwana began a slow movement from the south that led it to collide with Eurasia.
- About 251 million years ago there was the unification of the continents in Pangea a gigantic supercontinent with the Tethys Sea inside and surrounded by the Panthalassa Ocean.
- 200 million years ago began separation of Pangea the continents began to move to their current position and the rest of the oceans were formed.
Continental drift and plate tectonics
In the late 1960s, and more than fifty years after the presentation of Wegener's theory of continental drift, the theory of plate tectonics was postulated. This was based on the geological studies that preceded it, including Wegener's own theory and Harry Hess's theory of ocean floor spreading, from 1960.
The theory of plate tectonics maintains that the Earth's crust is divided into large continental and oceanic blocks called tectonic plates. These blocks are located in the part of the upper mantle closest to the crust, called the asthenosphere. The asthenosphere is composed of molten materials that are in continuous movement, and it is these movements that cause the movement of the tectonic plates that are above it.
Unlike Wegener's theory of continental drift, which was not accepted at the time, Currently the theory of plate tectonics is the most accepted to explain the movement of the continents and the formation of emerged and submerged reliefs, such as mountains and continental and submarine volcanoes.
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References
- Gil, A. (2020). The map of tectonic plates. The World Order. https://elordenmundial.com/
- National Geographic. (2023). What are tectonic plates and what causes their movements?. https://www.nationalgeographic.es/
- Tarbuck, E. and Lutgens, F. (2005). Earth Sciences. An introduction to physical geology. Prentice Hall.