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October 26.docx

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Department
Earth Sciences
Course
ESS102H1
Professor
C.Banks
Semester
Fall

Description
October 26 Expanding Earth versus Sea-Floor Spreading - traits of “critical thinking” and characteristics of a good scientist: o reasonable scepticism towards ideas o being open to reconsider one’s position o trust in reason, judgement not based on emotion - today look at a controversy using papers written by two very prominent proponents of plate tectonics 1. Expanding Earth o Tuzo Wilson 1908-1993)  first geophysics undergrad in Canada  worked at the Geological Survey  Physics Professors at UofT (1946-1974)  founder of Science North in Sudbury  first non-American president of AGU (AGU altered its constitution to allow this)  in a 1960 paper Wilson argued in favour of “Expanding Earth” • “...the foregoing hypothesis has the merit of appearing to explain many features of the Earth’s surface, though this does not constitute a proof.”  Wilson’s arguments: 1. Two possible causes for Earth’s expansion  decrease of gravitational constant  phase changes within Earth, and/or differentiation of core and mantle 2. Effect  circumference increased by 1,100 miles  average rate of 0.5 mm/year 3. Only mid-ocean ridges (not complete ocean basins) have grown throughout geologic time  matching observations/consequences • high-heat flow at mid-ocean ridges (MOR) • shallow earthquakes at MOR • buckling of Earth away from MOR (distance to MOR may be necessary condition) • J-shape of MOR and continents may show initial fracturing • some drift of continents possible but polar wander due to changing moment of inertia  facts/explanations in Wilson’s paper • mechanism: • ocean ridges: • high heat flow at ridges: • fit of continents: • mountain building: • polar wandering: • objection to Wegener’s “plowing” continents: • youth of ocean basins 2. Sea-Floor Spreading
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