"Doesn't the east coast of South America fit exactly against the west coast of Africa, as if they had once been joined?” "This is an idea I'll have to pursue.” - letter to his future wife, December 1910 Alfred Lothar Wegener (1880-1930) Alfred W. Turns out, he wasn’t the first. Francis Bacon noticed this in the 1600s. In 1858, geographer Antonio Snider-Pellegrini made these two maps showing his version of how the American and African continents may once have fit together, then later separated. Evidence for continental drift: 1) The shapes of continents match 2) The rocks match 3) The plants match 4) The ice matches Yet, the current positions don’t match A ghoulish Alfred A younger Alfred A colder Alfred Glacial evidence This all lead to a theory… CONTINENTAL DRIFT The continents have moved around the globe over time. They were all together about 250 Million years ago (I’ll call it Pangea, meaning “all the Earth” in Greek) There was a southern megacontinent (Gondwana) and a northern mega-continent (Laurasia). …and a whole lot of criticism. "Utter, damned rot!” -W.B. Scott "If we are to believe [this] hypothesis, we must forget everything we have learned in the last 70 years and start all over again” -American scientist "Wegener's hypothesis in general is of the footloose type, in that it takes considerable liberty with our globe, and is less bound by restrictions or tied down by awkward, ugly facts than most of its rival theories." - Dr. Rollin T. Chamberlin, University of Chicago This sounds like our kind of criticism. I’ve seen better films on laundry detergent. A break in the action: What makes a good scientific theory? Scientific Theory - A hypothesis or group of hypotheses that: 1) Explains scientific observations; 2) Is tested with repeated experiments and observations and found always to work; and 3) Is accepted by the scientific community. A good scientific theory: 1) Logical consistency 2) Agrees with the data. 3) Verifiable causes that explain and predict 4) Advanced comparisons (simplicity, tradeoff of generality and specificity, distinction between non-fatal difficulties and fatal difficulties) Is continental drift a good theory? - Self consistent - Agreed with available data - Made specific, testable predictions - Had difficulties, but weren’t fatal ones Do you think people know that we started our careers as German arctic meterologists, Statler? Ah, to be young and freezing cold again, Waldorf. Implications 1) The older concept of land bridges to explain fossil distributions became less likely. 2) The concept of a mobilistic Earth is brought forward. 3) It allowed scientist to start making predictions about fossil distributions, geological structures, and earthquakes. H. Cloos (famous geologist) It placed an easily comprehensible, tremendously exciting structure of ideas upon a solid foundation. It released the continents from the Earth's core and transformed them into icebergs of gneiss [granite] on a sea of basalt. It let them float and drift, break apart and converge. Where they broke away, cracks, rifts, trenches remain; where they collided, ranges of folded mountains appear. 1950s: The bathymetry of the ocean floor. Bruce Heezen Marie Tharp Harry Hess 1963 Fred Vine and Drummand Matthews In 1967, W. Jason Morgan proposed that the Earth's surface consists of 12 rigid plates that move relative to each other. Two months later, in 1968, Xavier Le Pichon published a complete model based on 6 major plates with their relative motions.