Wegener said the rocks had formed side-by-side and that the land had since moved apart. Mountain ranges with the same rock types, structures, and ages are now on opposite sides of the Atlantic Ocean.
Wegener concluded that they formed as a single mountain range that was separated as the continents drifted. Ancient fossils of the same species of extinct plants and animals are found in rocks of the same age but are on continents that are now widely separated figure 3.
Wegener proposed that the organisms had lived side by side, but that the lands had moved apart after they were dead and fossilized. He suggested that the organisms would not have been able to travel across the oceans. Fossils of the seed fern Glossopteris were too heavy to be carried so far by wind. Mesosaurus was a swimming reptile but could only swim in fresh water. Cynognathus and Lystrosaurus were land reptiles and were unable to swim Figure 3. Grooves and rock deposits left by ancient glaciers are found today on different continents very close to the equator.
Today glaciers only form on land and nearer the poles. Wegener thought that the glaciers were centered over the southern land mass close to the South Pole and the continents moved to their present positions later on.
Coral reefs and coal-forming swamps are found in tropical and subtropical environments, but ancient coal seams and coral reefs are found in locations where it is much too cold today. Wegener suggested that these creatures were alive in warm climate zones and that the fossils and coal later had drifted to new locations on the continents. Magnetic Polarity on the Same Continent with Rocks of Different Ages Geologists noted important things about the magnetic polarity of different aged rocks on the same continent: Magnetite crystals in fresh volcanic rocks point to the current magnetic north pole figure 5 no matter what continent or where on the continent the rocks are located.
Older rocks that are the same age and are located on the same continent point to the same location, but that location is not the current north magnetic pole. Older rock that are of different ages do not point to the same locations or to the current magnetic north pole. There are three possible explanations for this: The continents remained fixed and the north magnetic pole moved. The north magnetic pole stood still and the continents moved. Both the continents and the north pole moved.
Magnetic Polarity on Different Continents with Rocks of the Same Age Geologists noted that for rocks of the same age but on different continents, the little magnets pointed to different magnetic north poles.
The evidence for continental drift included the fit of the continents; the distribution of ancient fossils, rocks, and mountain ranges; and the locations of ancient climatic zones.
Although the evidence for continental drift was extremely strong, scientists rejected the idea because no mechanism for how solid continents could move around on the solid earth was developed. Later, recovering from wounds he suffered while fighting for Germany during World War I, he developed his idea in a book, The Origin of Continents and Oceans , published in German in When it was published in English, in , the intellectual fireworks exploded.
But it was the Americans who came down hardest against continental drift. The most poignant attack came from a father-son duo. Chamberlin had launched his career with an iconoclastic attack on establishment thinking. He went on to define a distinctly democratic and American way of doing science, according to historian Naomi Oreskes.
By the s, Chamberlin was the dean of American science and his colleagues fawned that his originality put him on a par with Newton and Galileo. Rollin T. For decades afterward, older geologists warned newcomers that any hint of an interest in continental drift would doom their careers. Wegener took the assault as an opportunity to refine his ideas and address valid criticisms. When critics said he had not presented a plausible mechanism for the drift, he provided six of them including one that foreshadowed the idea of plate tectonics.
Alternating patterns of magnetic anomalies on the ocean floor indicated seafloor spreading , where new plate material is born. Magnetic minerals aligned in ancient rocks on continents also showed that the continents have shifted relative to one another. A map of the continents inspired Wegener's quest to explain Earth's geologic history. Trained as a meteorologist, he was intrigued by the interlocking fit of Africa's and South America's shorelines. Wegener then assembled an impressive amount of evidence to show that Earth's continents were once connected in a single supercontinent.
Wegener knew that fossil plants and animals such as mesosaurs , a freshwater reptile found only South America and Africa during the Permian period, could be found on many continents. He also matched up rocks on either side of the Atlantic Ocean like puzzle pieces. In fact, plates moving together created the highest mountains in the world, the Himalayans, and the mountains are still growing due to the plates pushing together, even now, , according to National Geographic.
Despite his incredible evidence for continental drift, Wegener never lived to see his theory gain wider acceptance. He died in at age 50 just two days after his birthday while on a scientific expedition in Greenland, according to the University of Berkley.
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