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notes chaps 1-4 - The Earth System Topics 1 The Scientific...

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The Earth System  17:40 Topics 1. The Scientific Method 2. Discovery of a layered earth – an illustration of the scientific method 3. Earth as a system of interacting components  4. The geologic record (geo-clues) 5. Overview of geologic time  The Scientific Method The Goal: explain how natural phenomena works  Based on methodical observation and experiments to develop a tentative,  testable  hypothesis  (multiple) Challenge the hypotheses until it is a  theory  Develop a  scientific model  to represent some aspect of nature (Figure 1-1 in  textbook) Discovery of a Layered Earth  Key Observations     Density   o Surface rock density is relatively low: e.g. granite is 2.7 g/cm3 o However, the whole earth density is 5.5 g/cm3  (mass-gravity relation) o Mantle nodules in volcanic rocks have higher density (~ 3.5 g/cm3) o Core density must be about 8 g/cm3 – and this – matched iron-nickel  meteorites 
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Seismic Wave Behavior o Compression (P) and shear (S) waves behave differently and are bent,  absorbed or reflected at layer boundaries within the earth P waves = compressional (faster); S waves = shear (slower) P waves travel through solids, liquids, and gases  S waves travel only through solids  o Their travel velocity depends on the density of material  What we know: o Crust, mantle, molten outer core, solid inner core o The Crust : continents are made of lighter rock and thus literally “float” on  material of higher density – compositional break (Moho discontinuity)  o Outer Core : liquid iron  o Inner Core : solid iron  Abrupt changes in density between earth’s major interior layers are caused by  changes in the chemical composition of those layers There is also a very distinctive compositional change: the crust rocks are  made mostly of oxygen and silicon. In the mantle there is much more  magnesium and the the core had large amounts of iron. Heating and Differentiation of the Earth o Accretion      (kinetic energy added) o Compression      (gravitational and kinetic energy addition) o Radioactive elements      (spontaneous decay releases heat – long-lived  heating effect) o Started with a molten earth, but then things began to separate o Lighter things rose and created the crust and dense things like iron sank to  the core  The Earth System 
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The earth system relates to the interactions of all the geosystems (Figure 1- 10) o Climate system  Involves interactions between the atmosphere, hydrosphere,  cryosphere, biosphere, and lithosphere o Plate tectonic system  Involves interactions between the lithosphere, asthenosphere, and 
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