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BIO211H5 (55)

Sep 7.doc

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Jessica Hawthorn

BIO211 Sept 7 th Earth Origin and Structure Origin of Universe - age of the universe: big bang approx 15 billion years ago - planets formed near time of sun’s formation o about 4.6 billion years ago - outer planets composed of volatile elements - inner planets are rocky Origin of Earth - earth materials differentiated o densest at the center o less dense silicates rose to surface; cooled to form crust - meteorite impacts increased concentrations of some elements in upper earth o crust (0-40 km) o mantle (40-2890 km) o liquid iron core (2890-5150 km) o solid iron core (5150-6370 km) Origin of Moon - moon formed from impact of a protoplanet with earth - proportions of iron and magnesium differ from earth’s mantle o contribution from the colliding protoplanet? Origin of Continents - earliest crust was made up of relatively dense oceanic basalts (fine-grained volcanic rocks) - felsics (rocks rich in silicate materials) differentiated to form nuclei of continental crusts o modern analogue: Iceland – border between 2 tectonic plates - felsics: high in silicate minerals – oxygen and silicone - mafic: high in magnesium and iron - oceanic crust: denser and heaver, more mafic - continental: lighter, less dense, felsic - oldest rocks on earth are small archean fragments o high heat flow limited continental thickness o zircon crystals: 4.1-4.2 billion years old o
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