EAS210 Study Guide - Final Guide: Continental Crust, Oceanic Crust, Partial Melting

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Document Summary

Universe originally 98% hydrogen and helium, 2% heavier elements. Heavier elements came from nucleosynthesis (dying stars) Primitive crust formed as lighter, silica rich material and solidified at surface. Early crust recycled to form continental crust ~2. 5 ga. Oceanic crust continues to be formed and recycled today. Made up of lower density (~2. 7g/cm^3) silica rich rocks. Averages 7km thick (3-15km) made up of higher density (~3. 0g/cm^3) silica poor rocks. Rigid outer layer which includes the crust and part of the upper mantle. Seen by change in speed of seismic waves. The boundary between asthenosphere and lithosphere is seen by the composition of rocks. Poor in silica and rich in magnesium and iron. Lighter crust floats" on underlying denser ultramafic rocks. Blocks of same mass but differing density. Thick continental crust rises higher than thinner continental crust (mountains) Note that seawater does not affect crusts it just fills in the low places.