What evidence supported wegenes hypothesis of continental drift?

Question

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Answer 1

He was Alfred Wegener, and he put forward his hypothesis in about 1912. His only evidence for it at first was the way South America and Africa fit together like two pieces of a jigsaw puzzle. Further investigation showed some remarkable similarities in geological details on a smaller scale, just as would be expected if the two continents had once been joined. But all that the scientists could say was that it MIGHT just be chance, and since nobody could imagine any force that would move a whole continent a few thousand miles, that's the way things were left for a long time.

By 1960, calculations had made it pretty clear that the earth's metal core was generating more heat than could be conducted through the mantle, so the thermal balance had to be kept by the whole mantle (between the core and the crust) slowly convecting like a great big pan of barely-melted thick syrup. At the surface, this huge turning motion provided the sideways force that nobody had been able to think of. Other evidence from fossilised magnetism in old lava flows confirmed that hardly anywhere on earth was still where it used to be!

It's still going on. Very early results from satellite positioning systems showed that North America and Europe are moving away from each other at an inch or two every year.

Answer 2

Wegener used multiple lines of evidence to support his theory of continental drift.

Geomorphic arguments: Post glacial rebound (isostasy) as evidenced by raised shorelines in the Fennoscandia (Scandinavian) region. In North American similar raised shorelines of 500 meters around Hudson Bay.

Geophysical arguments: Based on the elevation of the land surfaces and known undersea depths, Wegener was able to draw several hypsometric curves that relate elevation (depth) to the total area at that elevation (depth). He noticed that rather than a normal distribution of heights and depths, the continents and oceans have two very distinct, and different, average values.

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. Without going 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. Most of the earthquakes that the German seismometer recorded define the edges of the Pacific Plate and are coincidentally situated along the "Ring of Fire". The ring of Fire are the volcanoes that surround the Pacific Plate.

Wegener also used the fact that the magnetic poles were known to be wandering to help support his theory. The Apparent Polar Wander (APW) curves for South America and Africa do not match. That can be explained by 1) two poles different poles affecting the two different continents or 2) one pole, but the two continents are moving relative to one another.

Geological arguments: Looking at the geology along the eastern edge of South America and the western edge of Africa, Wegener was able to point out striking similarities in the geology. Since then, certain lithologic units, e.g., the Parana Basalts and the Karoo Basalts have been 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 have the same age and could only be caused by the same thing - glaciation.

In 1906 the Great San Francisco Earthquake took place. Wegener used that fact that the earthquake occurred along the San Andreas Fault to help explain the idea that the Pacific and North American plates were drifting past one another there.

Plates could drift past one another, like along the San Andreas Fault in California, or they could rift apart from one another. This rifting produces areas of continental crust that is upthrown (horst) or downthrown (graben). These horst and graben are seen most easily in the Basin 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.

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

Paleontological and biological arguments: Wegener used information know about both extinct species (fossils) and living species (extant organisms) to help support his theory that the continents had once been attached. such as the ditribution of earthworm famalies. It's pretty hard to imagine the same earthworm family being in North America, South America, and Africa unless the continents were once connected.

Based on all that evidence, which pleased the biologists, 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.

His theory of continental drift did not propose a mechanism.

Answer 3

While at Marburg, in the autumn of 1911, Wegener was browsing in the university library when he came across a scientific paper that listed fossils of identical plants and animals found on opposite sides of the Atlantic. Intrigued by this information, Wegener began to look for, and find, more cases of similar organisms separated by great oceans. Orthodox science at the time explained such cases by postulating that land bridges, now sunken, had once connected far-flung continents. But Wegener noticed the close fit between the coastlines of Africa and South America. Might the similarities among organisms be due, not to land bridges, but to the continents having been joined together at one time? As he later wrote: "A conviction of the fundamental soundness of the idea took root in my mind." Such an insight, to be accepted, would require large amounts of supporting evidence. Wegener found that large-scale geological features on separated continents often matched very closely when the continents were brought together. For example, the Appalachian mountains of eastern North America matched with the Scottish Highlands, and the distinctive rock strata of the Karroo system of South Africa were identical to those of the Santa Catarina system in Brazil. Wegener also found that the fossils found in a certain place often indicated a climate utterly different from the climate of today: for example, fossils of tropical plants, such as ferns and cycads, are found today on the Arctic island of Spitsbergen. All of these facts supported Wegener's theory of "continental drift." In 1915 the first edition of The Origin of Continents and Oceans, a book outlining Wegener's theory, was published; expanded editions were published in 1920, 1922, and 1929. About 300 million years ago, claimed Wegener, the continents had formed a single mass, called Pangaea (from the Greek for "all the Earth"). Pangaea had rifted, or split, and its pieces had been moving away from each other ever since. Wegener was not the first to suggest that the continents had once been connected, but he was the first to present extensive evidence from several fields.

Answer 4

1. Look at all the continents, they all fit together like jigsaw puzzle.
2. plate Tectonics, The motions of regions of Earth's crust, which drift with respect to one another. Also known as continental drift.
3. Similar fossils on opposite sides of the ocean.
4.Coal can be found underneath the cold and dry Antarctic ice cap, though coal can only form in warm and wet conditions.

Answer 5

Whose hypothesis???
1. match of continental outlines (like a jigsaw puzzle)
2. isolated species with no counterpart on other continents

Answer 6

http://en.wikipedia.org/wiki/Continental_drift