AST251H1 Lecture Notes - Lecture 4: Plate Tectonics, Oceanic Crust, Solar Wind
16 Oct 2015
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Igneous solidified molten rock: basalt dark, dense, composed of iron and magnesium, granite lighter, less dense, contains silicate admixture, metamorphic transformed by high pressure or heat, sedimentary gradual compression of sentiments. If possible, we would tend to use the elements appropriate for the time scale of interest. Differentiation: separation by density, heavy materials (metals) sink to centre, lighter materials rise, iron/nickel sinks towards core, silicates get pushed to surface. Moon: dark spots on moon (mare) are craters billions of years old which filled with lava and cooled, radioactivity causes molten to seep into craters formed by accretion. Comets delivered water: we think that comets have retained old, unprocessed material reflecting the original composition of out proto-planetary nebula, they probably brought water-ice to earth. Atmosphere: gravity objects masses have attractive masses on each other, escape speed: speed at which the kinetic energy is equal to the gravitational potential energy, vesc = (2gm/d)1/2.
