the work of Alfred Wegener

7/31/2019 the work of Alfred Wegener

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If you look at the frequency distributions, these two maxima become very apparent.

Note only did Wegener look at the current hypsometric data, but he also hypothesized about past and future hypsometric curves. Withoutgoing into too much detail, the curves will become more and more separated owing to continued evolution and differentiation of the Earth.

Wegener also had access to seismologic records from Hamburg. Here, we can see that most of the earthquakes that the Germanseismometer recorded define the edges of the Pacific Plate and are coincidentally situated along the "Ring of Fire". The ring of Fire are thevolcanoes that surround the Pacific Plate.

Wegener also used the fact that the magnetic poles were known to be wandering to help support his theory. Below we can see the ApparentPolar Wander (APW) curves for South America (on the left) and Africa (on the right). Note that the two curves do not match. That can beexplained by 1) two poles different poles affecting the two different continents or 2) one pole, but the two continents are moving relative toone another.

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Geological arguments: Looking at the geology along the eastern edge of South America and the western edge of Africa, Wegener wasable to point out striking similarities in the geology. Since then, certain lithologic units, e.g., the Parana Basalts and the Karoo Basalts havebeen shown to have very similar major and minor element geochemistries.

Not only are there rocks on continents that once look like they fit together, but there are rocks on many of the southern continents that all havethe same age and could only be caused by the same thing - glaciation.



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In 1906 the Great San Francisco Earthquake took place. Wegener used that fact that the earthquake occurred along the San Andreas Faultto help explain the idea that the Pacific and North American plates were drifting past one another there. In the diagram below he indicatesthat the North American plate is moving south relative to the Pacific plate (which is moving north) near San Francisco.

Plates could drift past one another, like along the San Andreas Fault in California, or they could rift apart from one another. This ri ftingproduces areas of continental crust that is upthrown (horst) or downthrown (graben). These horst and graben are seen most easily in theBasin and Range Province of the Western United States, e.g., Nevada.

Not only can the continents rift apart and form the Basin and Range, but in some cases the rifting has opened new sea, e.g., the Red Sea in

the Afar triangle region. After a continent has fully rifted apart, mature oceans will form between the two new continents.



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If continents collided they would form zones of compression which Wegener knew to be island arcs, like the Aleutians Islands. Although hecorrectly identified island arcs as having something to do with collisional plate boundaries, Wegener didn't correctly understand the reason fortheir formation.

Paleontological and biological arguments: Wegener used information know about both extinct species (fossils) and living species (extantorganisms) to help support his theory that the continents had once been attached. Below we see the distribution of two modern families ofearthworms. It's pretty hard to imagine the same earthworm family being in North America, South America, and Africa unless the continents



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were once connected.

Based on all that evidence, which pleased the biologist, geographers, and paleontologist, but infuriated the geologists and geophysicists,Wegener proposed that the continents had once been connected to one another and had since split apart.

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the work of Alfred Wegener