2.28.08 - Oceanography Test #1

2.28.08 - Oceanography Test #1 - Oceanography Basics...

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Oceanography Basics SATELLITE RADAR ALTIMETRY: Technique used to determine heights and depths in areas of the world. Land measurements are not exact. Seafloor not directly measured. o Satellites measure height of the water, which translates into seafloor topography. THERE ARE ABOUT 1.4 BILLION KM 3 OF WATER ON OUR GLOBE. WATER COVERS 73% OF EARTH’S SURFACE. Oceans = 97% Ice = 2% Groundwater = < 1% Lakes, rivers = 0.01% Atmosphere = 0.001% TWO POSSIBLE SOURCES OF ALL THIS WATER: INTERIOR Volatiles escape from the earth. EXTERIOR Volatiles enter our atmosphere from elsewhere. SPECIFICALLY… 1. Degassing of the interior 2. Extraterrestrial delivery a. Water-rich meteorites Problem is that Earth’s atmosphere has very little xenon. Meteorites contain 3 magnitudes more xenon. Xenon signature would still be in our atmosphere. b. Cometary delivery of water Problem is that the D/H ratio of comets is twice as high as the D/H ratio of ocean water. The comet LINEAR, however, had a lot of water in it, and its D/H ratio is very similar to ocean water. BEST CURRENT MODEL FOR SOURCE OF OCEAN WATER: Combination of water derived from comets and water outgassed from Earth.
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Earth’s Crust PLATE CRUST 1. Oceanic crust is BALSALTIC. Derived by partial melting of the mantle: Rich in Fe, Mg dark color 2. Continental crust is GRANITIC. Derived by partial melting of oceanic crust: Rich in S, K light color Average density = 2.7 cc/g LAYERING OF CRUST AND CORE 1. Inner Core (Solid metal) 2. Outer Core (Liquid metal) 3. Mantle (Solid but plastic; can melt) 4. Crust (Solid and rigid) 5. Ocean and Atmosphere 1. The mantle and crust can undergo partial melting , causing fractionation. Partial melting : Different materials in mantle and crust melt, but others don’t. 2. Molten rock rises up New crustal rock of different makeup. WHY DO THE CONTINENTS STAND HIGH AND THE OCEAN LOW? a. Continental crust is less dense than oceanic crust. b. The plastic behavior of the upper mantle causes isostacy , the balance between upward force of buoyancy and downward force of gravity. c. Continental crust rides higher of the mantle and is thicker, so higher elevation. OTHER EFFECTS OF ISOSTATIC COMPENSATION Loading the crust causes it to sink (e.g. ice sheets) Unloading the crust causes it to rise (e.g. erosion)
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Seafloor Spreading Plate tectonics theory (circa 1960s) comes from observations of our active modern Earth. The tectonic plates are outlined by zones of tectonic activity. OBSERVATIONS
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This note was uploaded on 04/16/2008 for the course GEOS 104 taught by Professor Cox during the Spring '08 term at Williams.

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2.28.08 - Oceanography Test #1 - Oceanography Basics...

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