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4.1: Alfred Wegener and the Theory of Plate Tectonics - Geosciences

4.1: Alfred Wegener and the Theory of Plate Tectonics - Geosciences


If you look at a map of Earth, you may notice that some of the continents seem to fit together. An early reference to this phenomenon came from Francis Bacon in the 17th century, who noticed the similarities in the Atlantic coasts of Africa, and North and South America. This apparent fit is due to the fact the continents were once connected, and have since moved apart in what has been called continental drift. However, we now know that it is not just the continents that move, so a more correct term is plate tectonics. We can credit Alfred Wegener (Figure (PageIndex{1})) as the originator of this idea.

Alfred Wegener (1880-1930) earned a PhD in astronomy at the University of Berlin in 1904, but he had always been interested in geophysics and meteorology and spent most of his academic career working in meteorology. In 1911 he happened on a scientific publication that included a description of the existence of matching Permian-aged terrestrial fossils in various parts of South America, Africa, India, Antarctica, and Australia (Figure (PageIndex{2})). Wegener concluded that this distribution of fossils could only exist if these continents were joined together. Furthermore, some of these transcontinental areas have similar fossils until around 150 million years ago, then they begin to diverge, suggesting that the areas eventually separated and speciation took different paths on the separate continents. Wegener coined the term Pangaea (“all land”) for the supercontinent from which all of the present-day continents diverged.

Wegener pursued his theory with determination — combing the libraries, consulting with colleagues, and making observations — looking for evidence to support it. In addition to the fit of the continents and the fossil evidence, Wegener relied heavily on matching geological patterns across oceans, such as sedimentary strata in South America matching those in Africa (Figure (PageIndex{3})), North American coalfields matching those in Europe, and the mountains of Atlantic Canada matching those of northern Britain both in morphology and rock type.

Wegener also referred to the evidence for the Carboniferous and Permian (~300 Ma) Karoo Glaciation in South America, Africa, India, Antarctica, and Australia (Figure (PageIndex{4})). These areas contain evidence of past glacial deposits, including glacial scars oriented away from the poles, despite the fact that some of these locations are now tropical environments. This indicates that these continents were once closer to the south pole where the glaciers could have formed. Wegener argued that this could only have happened if these continents were once all connected as a single supercontinent. He also cited evidence (based on his own astronomical observations) that showed that the continents were moving with respect to each other, and determined a separation rate between Greenland and Scandinavia of 11 m per year, although he admitted that the measurements were not accurate. In fact they weren’t even close — the separation rate is actually about 2.5 cm per year!

Wegener first published his ideas in 1912 in a short book called Die Entstehung der Kontinente (The Origin of Continents), and then in 1915 in Die Entstehung der Kontinente und Ozeane (The Origin of Continents and Oceans). He revised this book several times up to 1929, and it was translated into French, English, Spanish, and Russian. However, despite his range of evidence, the continental fits were not perfect and the geological match-ups were not always consistent (while the continental fit left some gaps when using the current coastline, it was demonstrated in the 1960s that using a 500 m depth contour gives a much tighter fit). But the most serious problem of all was that Wegener could not conceive of a good mechanism for moving the continents around. Wegener proposed that the continents were like icebergs floating on heavier crust, but the only forces that he could invoke to propel continents around were poleflucht, the effect of Earth’s rotation pushing objects toward the equator, and the lunar and solar tidal forces, which tend to push objects toward the west. It was quickly shown that these forces were far too weak to move continents, and without any reasonable mechanism to make it work, Wegener’s theory was quickly dismissed by most geologists of the day. Alfred Wegener died in Greenland in 1930 while carrying out studies related to glaciation and climate. At the time of his death, his ideas were tentatively accepted by only a small minority of geologists, and soundly rejected by most. However, within a few decades that was all to change.


*”Physical Geology” by Steven Earle used under a CC-BY 4.0 international license. Download this book for free at http://open.bccampus.ca


4.1: Alfred Wegener and the Theory of Plate Tectonics - Geosciences

Alfred Wegener (1880-1930) (Figure 10.1) earned a PhD in astronomy at the University of Berlin in 1904, but he had always been interested in geophysics and meteorology and spent most of his academic career working in meteorology. In 1911 he happened on a scientific publication that included a description of the existence of matching Permian-aged terrestrial fossils in various parts of South America, Africa, India, Antarctica, and Australia (Figure 10.2).

Wegener concluded that this distribution of fossils could only exist if these continents were joined together during the Permian, and he coined the term Pangea (“all land”) for the supercontinent that he thought included all of the present-day continents.

Figure 10.1 Alfred Wegener a few years before his death in 1930 [http://upload.wikimedia.org/wikipedia/ commons/6/65/Alfred_Wegener_ca.1924-30.jpg]

Figure 10.2 The distribution of several Permian terrestrial fossils that are present in various parts of continents that are now separated by oceans. During the Permian, the supercontinent Pangea included the supercontinent Gondwana, shown here, along with North America and Eurasia.

Wegener pursued his theory with determination — combing the libraries, consulting with colleagues, and making observations — looking for evidence to support it. He relied heavily on matching geological patterns across oceans, such as sedimentary strata in South America matching those in Africa (Figure 10.3), North American coalfields matching those in Europe, and the mountains of Atlantic Canada matching those of northern Britain — both in morphology and rock type. Wegener also referred to the evidence for the Carboniferous and Permian (

300 Ma) Karoo Glaciation in South America, Africa, India, Antarctica, and Australia (Figure 10.4). He argued that this could only have happened if these continents were once all connected as a single supercontinent. He also cited evidence (based on his own astronomical observations) that showed that the continents were moving with respect to each other, and determined a separation rate between Greenland and Scandinavia of 11 m per year, although he admitted that the measurements were not accurate. In fact they weren’t even close — the separation rate is actually about 2.5 cm per year!

Figure 10.3 A cross-section showing the geological similarities between parts of Brazil on the left and Angola (Africa) on the right. The pink layer is a salt deposit, which is now known to be common in areas of continental rifting. [Source: U.S. Energy Information Administration (March 2015) http://www.eia.gov/countries/analysisbriefs/Angola/angola.pdf]

Figure 10.4 The distribution of the Carboniferous and Permian Karoo Glaciation (in blue) [SE, after http://upload.wikimedia.org/wikipedia/commons/9/96/Karoo_Glaciation.png]

Wegener first published his ideas in 1912 in a short book called Die Entstehung der Kontinente (The Origin of Continents), and then in 1915 in Die Entstehung der Kontinente und Ozeane (The Origin of Continents and Oceans). He revised this book several times up to 1929. It was translated into French, English, Spanish, and Russian in 1924.

In fact the continental fits were not perfect and the geological matchups were not always consistent, but the most serious problem of all was that Wegener could not conceive of a good mechanism for moving the continents around. It was understood by this time that the continents were primarily composed of sialic material (SIAL: silicon and aluminum dominated), and that the ocean floors were primarily simatic (SIMA: silicon and magnesium dominated). Wegener proposed that the continents were like icebergs floating on the heavier SIMA crust, but the only forces that he could invoke to propel continents around were poleflucht, the effect of Earth’s rotation pushing objects toward the equator, and the lunar and solar tidal forces, which tend to push objects toward the west. It was quickly shown that these forces were far too weak to move continents, and without any reasonable mechanism to make it work, Wegener’s theory was quickly dismissed by most geologists of the day.


4.1 Alfred Wegener’s Arguments for Plate Tectonics

Alfred Wegener (1880-1930 Figure 4.2) earned a PhD in astronomy at the University of Berlin in 1904, but had a keen interest in geophysics and meteorology, and focused on meteorology for much of his academic career.

Figure 4.2: Alfred Wegener during a 1912-1913 expedition to Greenland. Source: Alfred Wegener Institute (2008) Public Domain view source

In 1911 Wegener happened upon a scientific publication that described matching Permian-aged terrestrial fossils in various parts of South America, Africa, India, Antarctica, and Australia. He concluded that because these organisms could not have crossed the oceans to get from one continent to the next, the continents must have been joined in the past, permitting the animals to move from one to the other (Figure 4.3). Wegener envisioned a supercontinent made up of all the present day continents, and named it Pangea (meaning “all land”). He described the motion of the continents reconfiguring themselves as continental drift.

Figure 4.3: The distribution of several Permian terrestrial fossils that are present in various parts of continents now separated by oceans. During the Permian, the supercontinent Pangea included the supercontinent Gondwana, shown here, along with North America and Eurasia. Source: J.M. Watson, USGS (1999) Public Domainview source

Wegener pursued his idea with determination, combing libraries, consulting with colleagues, and making observations in an effort to find evidence in support of it. He relied heavily on matching geological patterns across oceans, such as sedimentary strata in South America matching those in Africa, North American coalfields matching those in Europe, the mountains of Atlantic Canada matching those of northern Britain—both in structure and rock type—and comparisons of rocks in the Canadian Arctic with those of Greenland (Figure 4.4).

Figure 4.4: Diagram from Alfred Wegener’s book Die Entstehung der Kontinente und Ozeane comparing rock types on Canadian Arctic Islands and Greenland. Source: Karla Panchuk (2018) CC BY 4.0. Click the image for more attributions.

Wegener also called upon evidence for the Carboniferous and Permian (

300 Ma) Karoo Glaciation from South America, Africa, India, Antarctica, and Australia (Figure 4.5). He argued that this could only have happened if these continents were once all connected as a single supercontinent. He also cited evidence (based on his own astronomical observations) that showed that the continents were moving with respect to each other, and determined a separation rate between Greenland and Scandinavia of 11 m per year, although he admitted that the measurements were not accurate. (The separation rate is actually about 2.5 cm per year.)

Figure 4.5: Carboniferous and Permian Karoo Glaciation in the southern hemisphere. Paleogeographic reconstruction for 306 million years ago._ Source: Cropped from C. R. Scotese, PALEOMAP Project (www.scotese.com) view source. Click the image for terms of use._

Wegener first published his ideas in 1912 in a short book called Die Entstehung der Kontinente (The Origin of Continents), and then in 1915 in Die Entstehung der Kontinente und Ozeane (The Origin of Continents and Oceans). He revised this book several times up to 1929. It was translated into French, English, Spanish, and Russian in 1924.

The main criticism of Wegener’s idea was that he could not explain how continents could move. Remember that, as far as anyone was concerned, Earth’s crust was continuous, not broken into plates. Thus, any mechanism Wegener could think of would have to fit with that model of Earth’s structure. Geologists at the time were aware that continents were made of different rocks than the ocean crust, and that the material making up the continents was less dense, so Wegener proposed that the continents were like icebergs floating on the heavier ocean crust. He suggested that the continents were moved by the effect of Earth’s rotation pushing objects toward the equator, and by the lunar and solar tidal forces, which tend to push objects toward the west. However, it was quickly shown that these forces were far too weak to move continents, and without any reasonable mechanism to make it work, Wegener’s theory was quickly dismissed by most geologists of the day.

Alfred Wegener died in Greenland in 1930 while carrying out studies related to glaciation and climate. At the time of his death, his ideas were tentatively accepted by a small minority of geologists, and firmly rejected by most. But within a few decades that was all to change.

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69 10.1 Alfred Wegener — the Father of Plate Tectonics

Alfred Wegener (1880-1930) (Figure 10.1) earned a PhD in astronomy at the University of Berlin in 1904, but he had always been interested in geophysics and meteorology and spent most of his academic career working in meteorology. In 1911 he happened on a scientific publication that included a description of the existence of matching Permian-aged terrestrial fossils in various parts of South America, Africa, India, Antarctica, and Australia (Figure 10.2).

Wegener concluded that this distribution of fossils could only exist if these continents were joined together during the Permian, and he coined the term Pangea (“all land”) for the supercontinent that he thought included all of the present-day continents.

Figure 10.1 Alfred Wegener a few years before his death in 1930 [http://upload.wikimedia.org/wikipedia/ commons/6/65/Alfred_Wegener_ca.1924-30.jpg]

Figure 10.2 The distribution of several Permian terrestrial fossils that are present in various parts of continents that are now separated by oceans. During the Permian, the supercontinent Pangea included the supercontinent Gondwana, shown here, along with North America and Eurasia.

Wegener pursued his theory with determination — combing the libraries, consulting with colleagues, and making observations — looking for evidence to support it. He relied heavily on matching geological patterns across oceans, such as sedimentary strata in South America matching those in Africa (Figure 10.3), North American coalfields matching those in Europe, and the mountains of Atlantic Canada matching those of northern Britain — both in morphology and rock type. Wegener also referred to the evidence for the Carboniferous and Permian (

300 Ma) Karoo Glaciation in South America, Africa, India, Antarctica, and Australia (Figure 10.4). He argued that this could only have happened if these continents were once all connected as a single supercontinent. He also cited evidence (based on his own astronomical observations) that showed that the continents were moving with respect to each other, and determined a separation rate between Greenland and Scandinavia of 11 m per year, although he admitted that the measurements were not accurate. In fact they weren’t even close — the separation rate is actually about 2.5 cm per year!

Figure 10.3 A cross-section showing the geological similarities between parts of Brazil on the left and Angola (Africa) on the right. The pink layer is a salt deposit, which is now known to be common in areas of continental rifting. [Source: U.S. Energy Information Administration (March 2015) http://www.eia.gov/countries/analysisbriefs/Angola/angola.pdf]

Figure 10.4 The distribution of the Carboniferous and Permian Karoo Glaciation (in blue) [SE, after http://upload.wikimedia.org/wikipedia/commons/9/96/Karoo_Glaciation.png]

Wegener first published his ideas in 1912 in a short book called Die Entstehung der Kontinente (The Origin of Continents), and then in 1915 in Die Entstehung der Kontinente und Ozeane (The Origin of Continents and Oceans). He revised this book several times up to 1929. It was translated into French, English, Spanish, and Russian in 1924.

In fact the continental fits were not perfect and the geological matchups were not always consistent, but the most serious problem of all was that Wegener could not conceive of a good mechanism for moving the continents around. It was understood by this time that the continents were primarily composed of sialic material (SIAL: silicon and aluminum dominated), and that the ocean floors were primarily simatic (SIMA: silicon and magnesium dominated). Wegener proposed that the continents were like icebergs floating on the heavier SIMA crust, but the only forces that he could invoke to propel continents around were poleflucht, the effect of Earth’s rotation pushing objects toward the equator, and the lunar and solar tidal forces, which tend to push objects toward the west. It was quickly shown that these forces were far too weak to move continents, and without any reasonable mechanism to make it work, Wegener’s theory was quickly dismissed by most geologists of the day.

Alfred Wegener died in Greenland in 1930 while carrying out studies related to glaciation and climate. At the time of his death, his ideas were tentatively accepted by only a small minority of geologists, and soundly rejected by most. However, within a few decades that was all to change. For more about his extremely important contributions to Earth science, visit this NASA website: http://earthobservatory.nasa.gov/Library/Giants/Wegener/


Evidence

Alfred Wegener collected diverse pieces of evidence to support his theory, including geological “fit” and fossil evidence. It is important to know that the following specific fossil evidence was not brought up by Wegener to support his theory. Wegener himself did not collect the fossils but he called attention to the idea of using these scientific doc uments stating there were fossils of species present in separate continents in order to support his claim.

Illustration showing similar rock assemblages across different continents.

Geological “fit” evidence is the matching of large-scale geological features on different continents. It has been noted that the coastlines of South America and West Africa seem to match up, however more particularly the terrains of separate continents conform as well. Examples include: the Appalachian Mountains of eastern North America linked with the Scottish Highlands, the familiar rock strata of the Karroo system of South Africa matched correctly with the Santa Catarina system in Brazil, and the Brazil and Ghana mountain ranges agreeing over the Atlantic Ocean.

Another important piece of evidence in the Continental Drift theory is the fossil relevance. There are various examples of fossils found on separate continents and in no other regions. This indicates that these continents had to be once joined together because the extensive oceans between these land masses act as a type of barrier for fossil transfer. Four fossil examples include: the Mesosaurus, Cynognathus, Lystrosaurus, and Glossopteris.

Modern day representation of the Mesosaurus.

The Mesosaurus is known to have been a type of reptile, similar to the modern crocodile, which propelled itself through water with its long hind legs and limber tail. It lived during the early Permian period (286 to 258 million years ago) and its remains are found solely in South Africa and Eastern South America. Now if the continents were in still their present positions, there is no possibility that the Mesosaurus would have the capability to swim across such a large body of ocean as the Atlantic because it was a coastal animal.

Modern day representation of the Cynognathus.

The now extinct Cynognathus, which translates to “dog jaw”, was a mammal- like reptile. Roaming the terrains during the Triassic period (250 to 240 million years ago), the Cynognathus was as large as a modern wolf. Its fossils are found only in South Africa and South America. As a land dominant species, the Cynognathus would not have been capable of migrating across the Atlantic.

Modern day representation of the Lystrosaurus.

The Lystrosaurus, which translates to “shovel reptile,” is thought to have been an herbivore with a stout build like a pig. It is approximated that it grew up to one meter in length and was relatively dominant on land during the early Triassic period (250 million years ago). Lystrosaurus fossils are only found in Antarctica, India, and South Africa. Similar to the land dwelling Cynognathus, the Lystrosaurus would have not had the swimming capability to traverse any ocean.

Modern day representation of the Glossopteris.

Possibly the most important fossil evidence found is the plant, Glossopteris. Known as a woody, seed bearing tree, the Glossopteris is named after the Greek description for tongue due to its tongue shaped leaves and is the largest genus of the extinct descendant of seed ferns. Reaching as tall as 30 meters, the Glossopteris emerged during the early Permian period (299 million years ago) and became the dominant land plant species until the end of the Permian. The Glossopteris fossil is found in Australia, Antarctica, India, South Africa, and South America—all the southern continents. Now, the Glossopteris seed is known to be large and bulky and therefore could not have drifted or flown across the oceans to a separate continent. Therefore, the continents must have been joined at least one point in time in order to maintain the Glossopteris’ wide range across the southern continents.

Description showing the fossil locations of the Mesosaurus, Cynognathus, Lystrosaurus, and Glossopteris spread across different continents.

If the continents of the Southern Hemisphere are put together, the distribution of these four fossil types form continuous patterns across continental boundaries. Of course, possible explanations are brought to attention. One explanation is the species could have migrated via a land bridge or swam to the other continents. However, a land bridge is not applicable due to the differences in densities between the continents and oceans floor and violation of the isostasy concept. Moreover, swimming as a possibility is foolish due to the lack of formidable swimming capabilities to travel across such an extensive body of water like the Atlantic. An additional resolution is that the species could have merely evolved separately on the other continents. Undoubtedly, this interpretation is in complete disagreement with Darwin’s evolution theory.


4.1 Plate Tectonics and Volcanism

The relationships between plate tectonics and volcanism are shown on Figure 4.1.1. As summarized in Chapter 3, magma is formed at three main plate-tectonic settings: divergent boundaries (decompression melting), convergent boundaries (flux melting), and mantle plumes (decompression melting).

Figure 4.1.1 The plate-tectonic settings of common types of volcanism. Composite volcanoes form at subduction zones, either on ocean-ocean convergent boundaries (left) or ocean-continent convergent boundaries (right). Both shield volcanoes and cinder cones form in areas of continental rifting. Shield volcanoes form above mantle plumes, but can also form at other tectonic settings. Sea-floor volcanism can take place at divergent boundaries, mantle plumes and ocean-ocean-convergent boundaries.

The mantle and crustal processes that take place in areas of volcanism are illustrated in Figure 4.1.2. At a spreading ridge, hot mantle rock moves slowly upward by convection (centimetre/year), and within about 60 kilometres (km) of the surface, partial melting starts because of decompression. Over the triangular area shown in Figure 4.1.2a, about 10% of the ultramafic mantle rock melts, producing mafic magma that moves upward toward the axis of spreading (where the two plates are moving away from each other). The magma fills vertical fractures produced by the spreading and spills out onto the sea floor to form basaltic pillows (more on that later) and lava flows. There is spreading-ridge volcanism taking place about 200 km offshore from the west coast of Vancouver Island.

Exercise 4.1 How thick is the oceanic crust?

Figure 4.1.2a shows a triangular zone about 60 km thick within this zone, approximately 10% of the mantle rock melts to form oceanic crust. Based on this information, approximately how thick do you think the resulting oceanic crust should be?

Figure 4.1.2 The processes that lead to volcanism in the three main volcanic settings on Earth: (a) volcanism related to plate divergence, (b) volcanism at an ocean-continent boundary (Similar processes take place at an ocean-ocean convergent boundary), and (c) volcanism related to a mantle plume.

At an ocean-continent convergent boundary, part of a plate that is made up of oceanic crust is subducting beneath part of another plate made up of continental crust. At an ocean-ocean convergent boundary, oceanic crust is being subducted beneath another oceanic-crust plate.[/footnote] (Figure 4.1.2b). In both situations the oceanic crust is heated up, and while there isn’t enough heat to melt the subducting crust, there is enough heat to force the water out of some of its minerals. This released water rises into the overlying mantle where it contributes to flux melting of the mantle rock. The mafic magma produced rises through the mantle to the base of the crust. There it contributes to partial melting of crustal rock, and thus it assimilates much more felsic material. That magma, now likely intermediate in composition, continues to rise and assimilate crustal material. In the upper part of the crust, it accumulates into plutons. From time to time, the magma from the plutons rises toward surface, leading to volcanic eruptions. Mount Garibaldi (Figures 4.0.1 and 4.0.2) is an example of subduction-related volcanism.

A mantle plume is an ascending column of hot rock (not magma) that originates deep in the mantle, possibly just above the core-mantle boundary. Mantle plumes are thought to rise approximately 10 times faster than the rate of mantle convection. The ascending column may be on the order of kilometres to tens of kilometres across, but near the surface it spreads out to create a mushroom-style head that is several tens to over 100 km across. Near the base of the lithosphere (the rigid part of the mantle), the mantle plume (and possibly some of the surrounding mantle material) partially melts to form mafic magma that rises to feed volcanoes. Since most mantle plumes are beneath the oceans, the early stages of volcanism typically take place on the sea floor. Over time, islands may form like those in Hawaii.

Volcanism in northwestern B.C. (Figures 4.1.3 and 4.1.4) is related to continental rifting. This area is not at a divergent or convergent boundary, and there is no evidence of an underlying mantle plume. A likely explanation is that the crust of northwestern B.C. is being stressed by the northward movement of the Pacific Plate against the North America Plate, and the resulting crustal fracturing provides a conduit for the flow of magma from the mantle. This may, or may not, be an early stage of continental rifting, such as that found in eastern Africa.

Figure 4.1.3 Volcanoes and volcanic fields in the Northern Cordillera Volcanic Province, B.C. Figure 4.1.4 Volcanic rock at the Tseax River area, northwestern B.C.


10.1 Alfred Wegener — the Father of Plate Tectonics

Alfred Wegener (1880-1930) (Figure 10.1) earned a PhD in astronomy at the University of Berlin in 1904, but he had always been interested in geophysics and meteorology and spent most of his academic career working in meteorology. In 1911 he happened on a scientific publication that included a description of the existence of matching Permian-aged terrestrial fossils in various parts of South America, Africa, India, Antarctica, and Australia (Figure 10.2).

Wegener concluded that this distribution of fossils could only exist if these continents were joined together during the Permian, and he coined the term Pangea (“all land”) for the supercontinent that he thought included all of the present-day continents.

Figure 10.1 Alfred Wegener a few years before his death in 1930 [http://upload.wikimedia.org/wikipedia/ commons/6/65/Alfred_Wegener_ca.1924-30.jpg]

Figure 10.2 The distribution of several Permian terrestrial fossils that are present in various parts of continents that are now separated by oceans. During the Permian, the supercontinent Pangea included the supercontinent Gondwana, shown here, along with North America and Eurasia.

Wegener pursued his theory with determination — combing the libraries, consulting with colleagues, and making observations — looking for evidence to support it. He relied heavily on matching geological patterns across oceans, such as sedimentary strata in South America matching those in Africa (Figure 10.3), North American coalfields matching those in Europe, and the mountains of Atlantic Canada matching those of northern Britain — both in morphology and rock type. Wegener also referred to the evidence for the Carboniferous and Permian (

300 Ma) Karoo Glaciation in South America, Africa, India, Antarctica, and Australia (Figure 10.4). He argued that this could only have happened if these continents were once all connected as a single supercontinent. He also cited evidence (based on his own astronomical observations) that showed that the continents were moving with respect to each other, and determined a separation rate between Greenland and Scandinavia of 11 m per year, although he admitted that the measurements were not accurate. In fact they weren’t even close — the separation rate is actually about 2.5 cm per year!

Figure 10.3 A cross-section showing the geological similarities between parts of Brazil on the left and Angola (Africa) on the right. The pink layer is a salt deposit, which is now known to be common in areas of continental rifting. [Source: U.S. Energy Information Administration (March 2015) http://www.eia.gov/countries/analysisbriefs/Angola/angola.pdf]

Figure 10.4 The distribution of the Carboniferous and Permian Karoo Glaciation (in blue) [SE, after http://upload.wikimedia.org/wikipedia/commons/9/96/Karoo_Glaciation.png]

Wegener first published his ideas in 1912 in a short book called Die Entstehung der Kontinente (The Origin of Continents), and then in 1915 in Die Entstehung der Kontinente und Ozeane (The Origin of Continents and Oceans). He revised this book several times up to 1929. It was translated into French, English, Spanish, and Russian in 1924.

In fact the continental fits were not perfect and the geological matchups were not always consistent, but the most serious problem of all was that Wegener could not conceive of a good mechanism for moving the continents around. It was understood by this time that the continents were primarily composed of sialic material (SIAL: silicon and aluminum dominated), and that the ocean floors were primarily simatic (SIMA: silicon and magnesium dominated). Wegener proposed that the continents were like icebergs floating on the heavier SIMA crust, but the only forces that he could invoke to propel continents around were poleflucht, the effect of Earth’s rotation pushing objects toward the equator, and the lunar and solar tidal forces, which tend to push objects toward the west. It was quickly shown that these forces were far too weak to move continents, and without any reasonable mechanism to make it work, Wegener’s theory was quickly dismissed by most geologists of the day.

Alfred Wegener died in Greenland in 1930 while carrying out studies related to glaciation and climate. At the time of his death, his ideas were tentatively accepted by only a small minority of geologists, and soundly rejected by most. However, within a few decades that was all to change. For more about his extremely important contributions to Earth science, visit this NASA website: http://earthobservatory.nasa.gov/Library/Giants/Wegener/


Contents

Early life and education

Alfred Wegener was born in Berlin on 1 November 1880 as the youngest of five children in a clergyman's family. His father, Richard Wegener, was a theologian and teacher of classical languages at the Berlinisches Gymnasium zum Grauen Kloster. In 1886 his family purchased a former manor house near Rheinsberg, which they used as a vacation home. Today there is an Alfred Wegener Memorial site and tourist information office in a nearby building that was once the local schoolhouse. [6] He was cousin to film pioneer Paul Wegener.

Wegener attended school at the Köllnisches Gymnasium on Wallstrasse in Berlin (a fact which is memorialized on a plaque on this protected building, now a school of music), graduating as the best in his class. Afterward he studied Physics, meteorology and Astronomy in Berlin, Heidelberg and Innsbruck. From 1902 to 1903 during his studies he was an assistant at the Urania astronomical observatory. He obtained a doctorate in astronomy in 1905 based on a dissertation written under the supervision of Julius Bauschinger at Friedrich Wilhelms University (today Humboldt University), Berlin. Wegener had always maintained a strong interest in the developing fields of meteorology and climatology and his studies afterwards focused on these disciplines.

In 1905 Wegener became an assistant at the Aeronautisches Observatorium Lindenberg near Beeskow. He worked there with his brother Kurt, two years his senior, who was likewise a scientist with an interest in meteorology and polar research. The two pioneered the use of weather balloons to track air masses. On a balloon ascent undertaken to carry out meteorological investigations and to test a celestial navigation method using a particular type of quadrant (“Libellenquadrant”), the Wegener brothers set a new record for a continuous balloon flight, remaining aloft 52.5 hours from 5–7 April 1906. [7]

First Greenland expedition and years in Marburg

In that same year 1906, Wegener participated in the first of his four Greenland expeditions, later regarding this experience as marking a decisive turning point in his life. The Denmark expedition was led by the Dane Ludvig Mylius-Erichsen and charged with studying the last unknown portion of the northeastern coast of Greenland. During the expedition Wegener constructed the first meteorological station in Greenland near Danmarkshavn, where he launched kites and tethered balloons to make meteorological measurements in an Arctic climatic zone. Here Wegener also made his first acquaintance with death in a wilderness of ice when the expedition leader and two of his colleagues died on an exploratory trip undertaken with sled dogs.

After his return in 1908 and until World War I, Wegener was a lecturer in meteorology, applied astronomy and cosmic physics at the University of Marburg. His students and colleagues in Marburg particularly valued his ability to clearly and understandably explain even complex topics and current research findings without sacrificing precision. His lectures formed the basis of what was to become a standard textbook in meteorology, first written In 1909/1910: Thermodynamik der Atmosphäre (Thermodynamics of the Atmosphere), in which he incorporated many of the results of the Greenland expedition.

On 6 January 1912 he publicized his first thoughts about continental drift in a lecture at a session of the Geologischen Vereinigung at the Senckenberg Museum, Frankfurt am Main and in three articles in the journal Petermanns Geographische Mitteilungen. [8]

Second Greenland expedition

After a stopover in Iceland to purchase and test ponies as pack animals, the expedition arrived in Danmarkshavn. Even before the trip to the inland ice began the expedition was almost annihilated by a calving glacier. The Danish expedition leader, Johan Peter Koch, broke his leg when he fell into a glacier crevasse and spent months recovering in a sickbed. Wegener and Koch were the first to winter on the inland ice in northeast Greenland. [9] Inside their hut they drilled to a depth of 25 m with an auger. In summer 1913 the team crossed the inland ice, the four expedition participants covering a distance twice as long as Fridtjof Nansen's southern Greenland crossing in 1888. Only a few kilometers from the western Greenland settlement of Kangersuatsiaq the small team ran out of food while struggling to find their way through difficult glacial breakup terrain. But at the last moment, after the last pony and dog had been eaten, they were picked up at a fjord by the clergyman of Upernavik, who just happened to be visiting a remote congregation at the time.

Family

Later in 1913, after his return Wegener married Else Köppen, the daughter of his former teacher and mentor, the meteorologist Wladimir Köppen. The young pair lived in Marburg, where Wegner resumed his university lectureship. There his two older daughters were born, Hilde (1914–1936) and Sophie ("Käte", 1918–2012). Their third daughter Hanna Charlotte ("Lotte", 1920–1989) was born in Hamburg. Lotte would in 1938 marry the famous Austrian mountaineer and adventurer Heinrich Harrer, while in 1939, Käte married Siegfried Uiberreither, Austrian Nazi Gauleiter of Styria. [10]

World War I

As an infantry reserve officer Wegener was immediately called up when the First World War began in 1914. On the war front in Belgium he experienced fierce fighting but his term lasted only a few months: after being wounded twice he was declared unfit for active service and assigned to the army weather service. This activity required him to travel constantly between various weather stations in Germany, on the Balkans, on the Western Front and in the Baltic region.

Nevertheless, he was able in 1915 to complete the first version of his major work, Die Entstehung der Kontinente und Ozeane (“The Origin of Continents and Oceans”). His brother Kurt remarked that Alfred Wegener's motivation was to “reestablish the connection between geophysics on the one hand and geography and geology on the other, which had become completely ruptured because of the specialized development of these branches of science.”

Interest in this small publication was however low, also because of wartime chaos. By the end of the war Wegener had published almost 20 additional meteorological and geophysical papers in which he repeatedly embarked for new scientific frontiers. In 1917 he undertook a scientific investigation of the Treysa meteorite.

Postwar period and third expedition

Wegener obtained a position as a meteorologist at the German Naval Observatory (Deutsche Seewarte) and moved to Hamburg with his wife and their two daughters. In 1921 he was appointed senior lecturer at the new University of Hamburg. From 1919 to 1923 Wegener did pioneering work on reconstructing the climate of past eras (now known as "paleoclimatology"), closely in collaboration with Milutin Milanković, [11] publishing Die Klimate der geologischen Vorzeit (“The Climates of the Geological Past”) together with his father-in-law, Wladimir Köppen, in 1924. [12] In 1922 the third, fully revised edition of “The Origin of Continents and Oceans” appeared, and discussion began on his theory of continental drift, first in the German language area and later internationally. Withering criticism was the response of most experts.

In 1924 Wegener was appointed to a professorship in meteorology and geophysics in Graz, which finally provided him with a secure position for himself and his family. He concentrated on physics and the optics of the atmosphere as well as the study of tornadoes. He had studied tornadoes for several years by this point, publishing the first thorough European tornado climatology in 1917. He also posited tornado vortex structures and formative processes. [13] Scientific assessment of his second Greenland expedition (ice measurements, atmospheric optics, etc.) continued to the end of the 1920s.

In November 1926 Wegener presented his continental drift theory at a symposium of the American Association of Petroleum Geologists in New York City, again earning rejection from everyone but the chairman. Three years later the fourth and final expanded edition of “The Origin of Continents and Oceans” appeared.

In 1929 Wegener embarked on his third trip to Greenland, which laid the groundwork for a later main expedition and included a test of an innovative, propeller-driven snowmobile.

Fourth and last expedition

Wegener's last Greenland expedition was in 1930. The 14 participants under his leadership were to establish three permanent stations from which the thickness of the Greenland ice sheet could be measured and year-round Arctic weather observations made. Wegener felt personally responsible for the expedition's success, as the German government had contributed $120,000 ($1.5 million in 2007 dollars). Success depended on enough provisions being transferred from West camp to Eismitte ("mid-ice") for two men to winter there, and this was a factor in the decision that led to his death. Owing to a late thaw, the expedition was six weeks behind schedule and, as summer ended, the men at Eismitte sent a message that they had insufficient fuel and so would return on 20 October.

On 24 September, although the route markers were by now largely buried under snow, Wegener set out with thirteen Greenlanders and his meteorologist Fritz Loewe to supply the camp by dog sled. During the journey, the temperature reached −60 °C (−76 °F) and Loewe's toes became so frostbitten they had to be amputated with a penknife without anesthetic. Twelve of the Greenlanders returned to West camp. On 19 October the remaining three members of the expedition reached Eismitte. There being only enough supplies for three at Eismitte, Wegener and Rasmus Villumsen took two dog sleds and made for West camp. They took no food for the dogs and killed them one by one to feed the rest until they could run only one sled. While Villumsen rode the sled, Wegener had to use skis, but they never reached the camp: Wegener died and Villumsen was never seen again. The expedition was completed by his brother, Kurt Wegener.

This expedition inspired the Greenland expedition episode of Adam Melfort in John Buchan's 1933 novel A Prince of the Captivity.

Death

Wegener died in Greenland in November 1930 while returning from an expedition to bring food to a group of researchers camped in the middle of an icecap. [14] He supplied the camp successfully, but there was not enough food at the camp for him to stay there. He and a colleague, Rasmus Villumsen, took dog sleds to travel to another camp although they never reached it. Villumsen had buried the body with great care, and a pair of skis marked the grave site. After burying Wegener, Villumsen had resumed his journey to West camp, but was never seen again. Six months later, on 12 May 1931, Kurt Wegener discovered his brother's grave halfway between Eismitte and West camp. He and other expedition members built a pyramid-shaped mausoleum in the ice and snow, and Alfred Wegener's body was laid to rest in it. [15] Wegener had been 50 years of age and a heavy smoker, and it was believed that he had died of heart failure brought on by overexertion. Villumsen was 23 when he died, and it is estimated that his body, and Wegener's diary, now lie under more than 100 metres (330 ft) of accumulated ice and snow. [ citation needed ]

Alfred Wegener first thought of this idea by noticing that the different large landmasses of the Earth almost fit together like a jigsaw puzzle. The continental shelf of the Americas fits closely to Africa and Europe. Antarctica, Australia, India and Madagascar fit next to the tip of Southern Africa. But Wegener only published his idea after reading a paper in 1911 which criticized the prevalent hypothesis, that a bridge of land once connected Europe and America, on the grounds that this contradicts isostasy. [16] Wegener's main interest was meteorology, and he wanted to join the Denmark-Greenland expedition scheduled for mid-1912. He presented his Continental Drift hypothesis on 6 January 1912. He analyzed both sides of the Atlantic Ocean for rock type, geological structures and fossils. He noticed that there was a significant similarity between matching sides of the continents, especially in fossil plants.

From 1912, Wegener publicly advocated the existence of "continental drift", arguing that all the continents were once joined together in a single landmass and had since drifted apart. He supposed that the mechanisms causing the drift might be the centrifugal force of the Earth's rotation ("Polflucht") or the astronomical precession. Wegener also speculated about sea-floor spreading and the role of the mid-ocean ridges, stating 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 sima [rising] from depth." [17] However, he did not pursue these ideas in his later works.

In 1915, in the first edition of his book, Die Entstehung der Kontinente und Ozeane, written in German, [18] Wegener drew together evidence from various fields to advance the theory that there had once been a giant continent, which he named "Urkontinent" [19] (German for "primal continent", analogous to the Greek "Pangaea", [20] meaning "All-Lands" or "All-Earth"). Expanded editions during the 1920s presented further evidence. (The first English edition was published in 1924 as The Origin of Continents and Oceans, a translation of the 1922 third German edition.) The last German edition, published in 1929, revealed the significant observation that shallower oceans were geologically younger. It was, however, not translated into English until 1962. [18]

Reaction

In his work, Wegener presented a large amount of observational evidence in support of continental drift, but the mechanism remained a problem, partly because Wegener's estimate of the velocity of continental motion, 250 cm/year, was too high. [21] (The currently accepted rate for the separation of the Americas from Europe and Africa is about 2.5 cm/year.) [22]

While his ideas attracted a few early supporters such as Alexander Du Toit from South Africa, Arthur Holmes in England [23] and Milutin Milanković in Serbia, for whom continental drift theory was the premise for investigating polar wandering, [24] [25] the hypothesis was initially met with skepticism from geologists, who viewed Wegener as an outsider and were resistant to change. [23] The one American edition of Wegener's work, published in 1925, which was written in "a dogmatic style that often results from German translations", [23] was received so poorly that the American Association of Petroleum Geologists organized a symposium specifically in opposition to the continental drift hypothesis. [26] The opponents argued, as did the Leipziger geologist Franz Kossmat, that the oceanic crust was too firm for the continents to "simply plough through".

From at least 1910, Wegener imagined the continents once fitting together not at the current shore line, but 200 m below this, at the level of the continental shelves, where they match well. [23] Part of the reason Wegener's ideas were not initially accepted was the misapprehension that he was suggesting the continents had fit along the current coastline. [23] Charles Schuchert commented:

During this vast time [of the split of Pangea] the sea waves have been continuously pounding against Africa and Brazil and in many places rivers have been bringing into the ocean great amounts of eroded material, yet everywhere the geographic shore lines are said to have remained practically unchanged! It apparently makes no difference to Wegener how hard or how soft are the rocks of these shore lines, what are their geological structures that might aid or retard land or marine erosion, how often the strand lines have been elevated or depressed, and how far peneplanation has gone on during each period of continental stability. Furthermore, sea-level in itself has not been constant, especially during the Pleistocene, when the lands were covered by millions of square miles of ice made from water subtracted out of the oceans. In the equatorial regions, this level fluctuated three times during the Pleistocene, and during each period of ice accumulation the sea-level sank about 250 feet [75 m]. [ citation needed ]

Wegener was in the audience for this lecture, but made no attempt to defend his work, possibly because of an inadequate command of the English language.

In 1943, George Gaylord Simpson wrote a strong critique of the theory (as well as the rival theory of sunken land bridges) and gave evidence for the idea that similarities of flora and fauna between the continents could best be explained by these being fixed land masses which over time were connected and disconnected by periodic flooding, a theory known as permanentism. [27] Alexander du Toit wrote a rejoinder to this the following year. [28]

In the early 1950s, the new science of paleomagnetism pioneered at the University of Cambridge by S. K. Runcorn and at Imperial College by P.M.S. Blackett was soon producing data in favour of Wegener's theory. By early 1953 samples taken from India showed that the country had previously been in the Southern hemisphere as predicted by Wegener. By 1959, the theory had enough supporting data that minds were starting to change, particularly in the United Kingdom where, in 1964, the Royal Society held a symposium on the subject. [29]

The 1960s saw several relevant developments in geology, notably the discoveries of seafloor spreading and Wadati–Benioff zones, and this led to the rapid resurrection of the continental drift hypothesis in the form of its direct descendant, the theory of plate tectonics. Maps of the geomorphology of the ocean floors created by Marie Tharp in cooperation with Bruce Heezen were an important contribution to the paradigm shift that was starting. Wegener was then recognized as the founding father of one of the major scientific revolutions of the 20th century.

With the advent of the Global Positioning System (GPS), it became possible to measure continental drift directly. [30]

The Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany, was established in 1980 on Wegener's centenary. It awards the Wegener Medal in his name. [31] The crater Wegener on the Moon and the crater Wegener on Mars, as well as the asteroid 29227 Wegener and the peninsula where he died in Greenland (Wegener Peninsula near Ummannaq, 71°12′N 51°50′W  /  71.200°N 51.833°W  / 71.200 -51.833 ), are named after him. [32]

The European Geosciences Union sponsors an Alfred Wegener Medal & Honorary Membership "for scientists who have achieved exceptional international standing in atmospheric, hydrological or ocean sciences, defined in their widest senses, for their merit and their scientific achievements." [33]


1.7 Chapter Review Questions

How does the element of time make geology different from the other sciences, such as chemistry and physics?

List three ways in which geologists can contribute to society.

The following dates are written with the abbreviations Ga, Ma, and ka. Express the dates in years. (For example, 2.3 Ma = 2,300,000 years)

Dinosaurs first appear in the geological record in rocks from about 215 Ma and then most became extinct at 65 Ma. What percentage of geological time does this represent?

If sediments typically accumulate at a rate of 1 mm/year, what thickness of sediment could accumulate over a period of 30 million years?

Does uniformitarianism mean that conditions on Earth are uniform, and never change?

Summarize the main idea behind plate tectonics.


10.1 Alfred Wegener: The Father of Plate Tectonics

Figure 10.1.1 Alfred Wegener a few years before his death in 1930.

Alfred Wegener (1880-1930) (Figure 10.1.1) earned a PhD in astronomy at the University of Berlin in 1904, but he had always been interested in geophysics and meteorology and spent most of his academic career working in meteorology. In 1911 he happened on a scientific publication that included a description of the existence of matching Permian-aged terrestrial fossils in various parts of South America, Africa, India, Antarctica, and Australia (Figure 10.1.2).

Wegener concluded that this distribution of terrestrial organisms could only exist if these continents were joined together during the Permian, and he coined the term Pangea (“all land”) for the supercontinent that he thought included all of the present-day continents.

Figure 10.1.2 The distribution of several Permian terrestrial fossils that are present in various parts of continents that are now separated by oceans. [Image Description]

Wegener pursued his theory with determination—combing the libraries, consulting with colleagues, and making observations—looking for evidence to support it. He relied heavily on matching geological patterns across oceans, such as sedimentary strata in South America matching those in Africa (Figure 10.1.3), North American coalfields matching those in Europe, and the mountains of Atlantic Canada matching those of northern Britain—both in morphology and rock type.

Figure 10.1.3 A cross-section showing the geological similarities between parts of Brazil (South America) on the left and Angola (Africa) on the right. The pink layer is a salt deposit, which is now known to be common in areas of continental rifting.

Wegener referred to the evidence for the Carboniferous and Permian (

300 Ma) Karoo Glaciation in South America, Africa, India, Antarctica, and Australia (Figure 10.1.4). He argued that this could only have happened if these continents were once all connected as a single supercontinent. He also cited evidence (based on his own astronomical observations) that showed that the continents were moving with respect to each other, and determined a separation rate between Greenland and Scandinavia of 11 metres per year, although he admitted that the measurements were not accurate. In fact they weren’t even close—the separation rate is actually about 2.5 centimetres per year!

Figure 10.1.4 The distribution of the Carboniferous and Permian Karoo Glaciation (outlined in blue).

Wegener first published his ideas in 1912 in a short book called Die Entstehung der Kontinente (The Origin of Continents), and then in 1915 in Die Entstehung der Kontinente und Ozeane (The Origin of Continents and Oceans). He revised this book several times up to 1929. It was translated into French, English, Spanish, and Russian in 1924.

In fact the continental fits were not perfect and the geological matchups were not always consistent, but the most serious problem of all was that Wegener could not conceive of a credible mechanism for moving the continents around. It was understood by this time that the continents were primarily composed of sialic material (SIAL: silicon and aluminum dominated, similar to “felsic”), and that the ocean floors were primarily simatic (SIMA: silicon and magnesium dominated, similar to “mafic”). Wegener proposed that the continents were like icebergs floating on the heavier SIMA crust, but the only forces that he could invoke to propel continents around were poleflucht, the effect of Earth’s rotation pushing objects toward the equator, and the lunar and solar tidal forces, which tend to push objects toward the west. It was quickly shown that these forces were far too weak to move continents, and without any reasonable mechanism to make it work, Wegener’s theory was quickly dismissed by most geologists of the day.

Alfred Wegener died in Greenland in 1930 while carrying out studies related to glaciation and climate. At the time of his death, his ideas were tentatively accepted by only a small minority of geologists, and soundly rejected by most. However, within a few decades that was all to change. For more about his extremely important contributions to Earth science, visit the NASA website to see a collection of articles on Alfred Wegener.

Image Descriptions

Figure 10.1.2 image description: Fossils found across different continents suggest that these continents were once joined as a super-continent. Fossil remains of Cynognathus (a terrestrial reptile) and Mesosaurus (a freshwater reptile) have been found in South America and Africa. Fossil evidence of the Lystrosaurus, a land reptile from the Triassic period, has been found in India, Africa, and Antarctica. Fossils of the fern Glossopteris have been found in Australia, Antarctica, India, Africa, and South America. When you position these continents so they fit together, the areas where these fossils were found line up. [Return to Figure 10.1.2]

Media Attributions

  • Figure 10.1.1: “Alfred Wegener ca.1924-30.” Public domain.
  • Figure 10.1.2: “Snider-Pellegrini Wegener fossil map” by Osvaldocangaspadilla. Public domain.
  • Figure 10.1.3: © Steven Earle. CC BY. Based on “Angola -Brazil sub-sea geology” by Cobalt International Energy can be found at U.S. Energy Information Administration: Country Analysis Brief: Angola (May 2016) [PDF].
  • Figure 10.1.4: “Karoo Glaciation” © GeoPotinga. Adapted by Steven Earle. CC BY-SA.

the supercontinent that existed between approximately 300 and 180 Ma

referring to rock or magma in which silica and aluminum are the predominant components (generally equivalent to felsic)

referring to rock or magma in which silica, magnesium and iron are the predominant components (generally equivalent to mafic)


Watch the video: Continental Drift Theory - Alfred Wegener. Pangea. Gondwanaland