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Plate Tectonics Evolution of the Theory of Continental Drift and the Movement of Earth’s Plates Historical Perspective of Plate Tectonics The Theory of Continental Drift was first purposed by German Scientist Alfred Wegener in 1912. This suggested that 250 million years ago the continents were linked together in a super continent that was called Pangaea. Can you see how these continents might have fitted together? Historical Perspectives of Plate Tectonics Wegener was not the first to suggest that the continents had moved. As early as 1596 a Dutch mapmaker Abraham Ortelius stated that he believed that the Americas had torn away from Europe and Africa! Abraham Ortelius’ World map! Which was very accurate for its time! 1858 Geographer Antonio Snider-Pellegrini noted and showed how well the continents could fit together. Historical Perspective of Plate Tectonics Wegener also believed that the continents had separated and shifted over time. He just was not sure how they had done so. He suggested that the landmasses had plowed through the oceans and into each other. He based his theory on several pieces of evidence including the fit of the continents, the occurrences of unusual geological structures, and the matching of plant and animal fossils across continents. Historical Perspective of Plate Tectonics His theory was rejected by other scientists, for some it was rejected because he could not provide an accurate method for the movement of the continents. South African geologist Alexander Du Toit further theorized that Pangaea divided into two supercontinents 205 million years ago. Du Toit called the northern supercontinent Laurasia and the southern one Gondwanaland. It would take another roughly 50 years before his theory was proven, and the method of plate movement was determined. Super Continents As I mentioned earlier Wegner and others proposed that all the continents today were once joined together in a super continent called PANGAEA! More Super Continents When Pangaea began to break up it separated into two distinct continents named by Du Toit as Laurasia and Gondwanaland. Movement of Continents The continents continue to move to their present locations. The Evidence for Continental Drift Wegener and Du Toit both mention the continents fitting together, the matching of geological structures such as mountain ranges, and plants and animal fossils. What is a Fossil? A Fossil is the evidence in rock of the presence of a plant or animal from an earlier geological period they are formed when replace the materials in tissues creating a the stone. minerals the bones and replica embedded in What Were The Fossils? Mesosaurus, a freshwater crocodile-like reptile that lived during the early Permian (between 286 and 258 million years ago), are found solely in Southern Africa and Eastern South America. It would have been physiologically impossible for Mesosaurus to swim between the continents. This suggests that South America and Africa were joined during the Early Permian. Cynognathus is an extinct mammal-like reptile. The name literally means ‘dog jaw’. Cynognathus was as large as a modern wolf and lived during the early to mid Triassic period (250 to 240 million years ago). It is found as fossils only in South Africa and South America. What Were The Fossils? Lystrosaurus, which literally means ‘shovel reptile,’ was dominant on land in the early Triassic, 250 million years ago. It is thought to have been herbivorous and grew to approximately one metre in length, with a stocky build like a pig. Fossils of Lystrosaurus are only found in Antarctica, India and South Africa. What Were The Fossils? Glossopteris was a woody, seed-bearing shrub or tree, named after the Greek description of ‘tongue’ – a description of the shape of the leaves. Some reached 30m tall. It evolved during the Early Permian (299 million years ago) and went on to become the dominant species throughout the period, not becoming extinct until the end of the Permian. Fossils are found in Australia, South Africa, South America, India and Antarctica. Recreate Pangaea We are going to cut up the continents and using the fossil, and tectonic evidence, as well as what we can see about how they might fit to try and recreate Pangaea. Discussion Questions Which two continents have the most obvious fit of the coastlines? Were the fossil symbols and mountain belts helpful in deciding where to move the continents? Why doesn’t the present shapes of the continents fit perfectly in to a supercontinent? Which fossil occurs on the most landmasses? What does this suggest about when these particular continents broke up? What is Evidence? Evidence is something that is presented in support of an assertion or idea! It can be strong evidence or weak evidence, depending on how well it proves the idea. Scientific evidence can be observations, or experimental findings just saying something is true, or not true, with no evidence to back it up is not proof! Evidence Worksheet! 2 cm a Year! Given the fact that we are still moving at 2 cm a year how long will it take us to move 10cm? 100cm? 1 Km? Current Theory of Plate Tectonics Harry Hammond Hess published ‘The History of Ocean Basins' in 1962, in which he outlined a theory that could explain how the continents could actually drift. This theory later became known as ‘Sea Floor Spreading'. Become know as Divergent and Convergent Faults John Tuzo Wilson proposed that plates might move over fixed hotspots in the mantle in 1965 he proposed a third type of plate boundary that he called Transform faults or Conservative Plate Boundaries. These faults move past each other horizontally – San Andreas Fault between North America and Pacific plates Current Theory of Plate Tectonics Dan McKenzie in mid 1960’s was working on convection in the Earth’s mantle at Cambridge University when he became interested in Continental Drift Theory he used his knowledge of thermodynamics to address the problem of how plates move. He suggested there are two layers in the mantle, each of which are in motion, controlling the movement and behavior of the tectonic plates above. ‘The Viscosity of the Lower Mantle’ was published in 1966. What’s Your Super Continent? Create your own jigsaw puzzle of continents with fossil evidence and tectonic evidence that will allow your partner to piece it back together once you break it apart Be Creative! What would you call your Super Continent?