Structure of the Earth

• Atmophiles: Gases or liquids at the earth's surface e.g. hydrogen, oxygen and nitrogen. Found in the Atmosphere
• Lithophiles: Very reactive metals that readily form compounds with oxygen e.g. silicon, aluminium, sodium. Found in the crust
• Chalcophiles: Readily form compunds with sulphur e.g copper, lead, zinc. Found in the Mantle
• Siderophiles: Form very dense compounds that include iron e.g. nickel, cobalt, tungsten. Found in the core
• Goldschmidt classified elements into four groups


  Atmophiles, Lithophiles, Chalcophiles and Siderophiles
• When the Earth first formed from accretion of dust and larger particles it became molten. Gravity then caused the compounds to seperate out 


  Siderophiles (densest) sank first, then chalcophiles, lithophiles, and finally atmophiles
• Discontinuity: Boundry where rock composition, density and state changes affecting seismic waves
• Direct evidence: Observation of rocks exposed at the surface e.g cliffs, cuttings, quarries


  Show the continents are a complex mix of igneous, sedimentary and metamorphic rocks, overlaying a granite basement up to 4 billion years old
• Direct evidence: observation of rocks in deep mines (up to 3.9km deep)


  Shows rocks are very old but similar and no oxygen was present in formation of the rocks
• Direct evidence: Observation of rocks from deep boreholes (up to 12.2km deep) 


  Rocks brought to the surface in cores are pretty similar to rocks that can be seen exposed
• Direct evidence: Observation of rocks brought up as xenoliths in deep volcanic vents


  + Occasionally fragments of peridotite from the mantle get caught up in the basalt making its way through pipes (vents) towards the surface

  + Diamonds form about 150km deep in the mantle at the base of cratons, they are found towards the surface through vents
• Peridotite: An ultramafic rock rich in minerals such as olivine and is occasionally brought up out of the mantle through vents
• Direct evidence: Ophiolite suites


  An ophiolite suite is a distinctive sequence of rocks which represent a piece of ocean lithosphere (including mantle rock) which has been obducted into a mountain range and then exposed by erosion