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Transcript
Continental Drift & Speciation Continental Drift • Alfred Wegener • In the 1930’s suggested that continents were (and are currently) moving relative to each other and that at some time in the past they were joined together forming a super continent Pangea Continental Geography • The eastern coast of South America and the western coast of Africa appear to fit nicely together like pieces of a puzzle Paleontology & Climate • The ranges of fossil plant and animal specimens of similar age appear to correlate well across current continental boundaries • Tropical fossils exist in Antarctic sediment suggesting that this continent has not always existed in its current location Past Glacial Events • Mapping of the extent of glacial rock remains on the different continent suggests particular connections between the continents in the past Plate Tectonics • Continental Drift was not taken seriously by the geological community until a mechanism that could explain the movement of the continents could be developed Ruggedness of the Ocean Floor • Through development of sonar and more extensive use of submarines a picture of a rugged sea floor emerged (previously it was thought that the ocean floor was flat) • In fact, the Earth’s largest feature is the Mid-Atlantic Ridge running down the middle of the Atlantic Ocean Oceanic Ridges • At ocean ridges new crust arises from magma within the Earth forcing the existing plate out while a new border for the plate is being made Magnetic Striping • As new magma cools magnetic crystals within it line up with the magnetic poles of the Earth • The north end facing north and the south end facing south • As magma in the Earth’s core circulates “magnetic or polar reversals” occur • Our current north and south flip such that the magnetic crystal line up opposite of what they would be normally. Oceanic Trenches • Where two plates come together one is subducted under the other forming a trench • Tension builds up in the plate laying on top while heat may generate magma below (Mts & Volcanoes) • Mapping of the distribution of Earthquakes across the globe correlates well with places were plates are coming together • http://pubs.usgs.gov/publications/text/ Information on Continental Drift and Plate Tectonics Speciation • Process by which: a) subpopulations of one species diverge becoming adapted to different environments and reproductively isolated b) descendants of a species become adapted to an environment different than the one in which it was originally adapted Allopatric Speciation • Type of speciation in which the subpopulations diverge because they are ‘separated by a geographic barrier’ Reproductive Isolation • Pre-Zygotic Mechanisms 1) Temporal 2) Behavioral 3) Mechanical 4) Ecological 5) Gametic Mortality • Post-Zygotic Mechanisms 1) Hybrid Inviability 2) Hybrid Sterility 3) Low Fitness Hybrids