His Principles of Physical Geology, ending with a chapter on continental drift, was published in 1944.
He proposed in 1931 that the Earth's mantle contained convection cells that dissipated radioactive heat and moved the crust at the surface. The British geologist Arthur Holmes championed the theory of continental drift at a time when it was unfashionable. Although continental drift explained many of Wegener's observations, he could not find scientific evidence to make a complete explanation of how continents move. Wegener said that because they are less dense, continents float on top of the denser rock of the ocean floor, and move across the ocean floor rock. He believed these similarities could be explained only if these geologic features were once part of the same continent. Also, he said that the rock strata in South Africa and Brazil were similar. For example, he said that there were geological similarities between the Appalachian Mountains in North America, and the Scottish Highlands. Wegener used geologic, fossil, and glacial evidence from opposite sides of the Atlantic Ocean to support his theory of continental drift. The first time was by the mapmaker Abraham Ortelius in the 16th century. Where theyīroke away, cracks, rifts, trenches remain where they collided, ranges of folded mountains appear.The theory had been proposed before, more than once. It let them float and drift, break apart and converge. It released the continents from the Earth's core and transformed them into icebergs of gneiss "It placed an easily comprehensible, tremendously exciting structure of ideas upon a solid foundation. Perhaps the best summary of Wegener's revolutionary theory was provided by countryman Hans Cloos: Started moving to their current positions. Pangaea (all lands), and said it began to break up about 200 million years ago, when the continents If they do, there is nothing left but toĬonclude that the pieces were in fact joined in this way.īy his third edition (1922), Wegener was citing geological evidence that some 300 million yearsĪgo all the continents had been joined in a supercontinent stretching from pole to pole. It is just as if we were to refit the torn pieces of a newspaper by matching their edges and thenĬheck whether the lines of print ran smoothly across. He also noted that when you fit Africa and South America together, mountain ranges (and coalĭeposits) run uninterrupted across both continents, writing: Wegener said they formed when the edge ofĪ drifting continent crumpled and foldedas when India hit Asia and formed the Himalayas. Occur in narrow bands, usually at the edge of a continent. If this were so, however, they should be spread evenly over the Earth instead mountain ranges
WHO WAS ALFRED WEGENER SKIN
According to the cooling,Ĭontracting-Earth theory, they formed on the Earth's crust as wrinkles form on the skin of a dryingĪpple. Wegener also offered a more plausible explanation for mountain ranges. (Map courtesy This Dynamic Earth, United States Brown indicates fossil evidence of the Triassic land reptile Lystrosaurus. Green indicates fossils of the fern Glossopteris,įound in all of the southern continents. Dark blue indicates fossil remains of the freshwater reptile Mesosaurus. In the above map, orange indicates the fossil remains of Cynognathus, a Wegener believed thisįact was one of the strongest pieces of evidence for his theory.
Was that the continents themselves had been joined and had since drifted apart.įossils appear in continuous bands across continents that are now separated by thousands of miles of ocean. Geological evidence clearly showed the continents were once connected, the only logical alternative Wegener reasoned that if continent-size land bridges had existed and somehow been forced to the oceanīottom, they would have "bobbed-up" again when the force was released.
WHO WAS ALFRED WEGENER PLUS
Given the difference in density between continents and sea floor, plus the process of isostasy, The weight of continental ice sheets in the last ice age, and their rise since the ice melted some As an example he cited the sinking of Northern Hemisphere lands under Wegener also noted that the continents move up and down to maintain equilibrium That makes up the deep-sea floor in which Wegener proposed that the continents floated somewhat like Out that the continents are made of a different, less dense rock (granite) than the volcanic basalt Wegener began by demolishing the theory that large land bridges had once connected the continentsĪnd had since sunk into the sea as part of a general cooling and contraction of the Earth. At the time of publication, it represented the best available science. This page contains archived content and is no longer being updated.