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aug 27 - theory evolved in the 1960s It explains unified...

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GLG 101, August 27, 2010 Polar Wander – each continent had a separate polar wander path. These curves align when continents are assembled. Apparent Polar Wander New Observations of Oceanic Crust – earthquakes Magnetic Anomalies – towed magnetometers measure ocean crust. Magnetism varies perpendicular to the Mid-Ocean ridge. These variations are + and – magnetic anomalies. Magnetic Reversals - layered lava flows reveal reversals in polarity (magnetic polarity is the direction of magnetic north). Reversals are geologically rapid. It can be used as time markers. Sea Floor Spreading: Proof – reversals in polarity explain magnetic anomalies. Positive anomalies – normal polarity crust. Negative anomalies – reversed polarity crust. Magnetic anomalies are symmetric across a mid-ocean ridge. Sea floor spreading – drilling in the late 1960s recovered crust samples. Plate Tectonics Earth’s outer shell is broken into rigid plates that move. Tectonic
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Unformatted text preview: theory evolved in the 1960s. It explains unified mechanisms such as igneous, sedimentary and metamorphic rocks, distribution of earthquakes and volcanoes, the origin of continents and ocean basins, the distribution of fossil plants and animals, the genesis and destruction of mountain chains, and continental drift. Lithosphere – made of both crust and the upper mantle. It is in motion over the asthenosphere. It bends elastically when loaded. Asthenosphere flows plastically when loaded. 2 types of lithosphere – continental ~150 km thick & oceanic ~7 to 100 km thick. Plate Boundaries – lithosphere is fragmented into ~20 tectonic plates. Plates move continuously at a rate of 1 to 15 cm/yr. Continental Margins – where land meets the ocean. (Margins near plate boundaries are “active”. Margins far from plate boundaries are “passive”.) 3 types of plate boundaries – divergent, convergent, transformed...
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