Evidence for the structure of the earth

Evidence for the structure of the earth

1. Direct

   • Geothermal gradient
     • The average geothermal gradient of the earth is about 25 degrees
     • The temperature gradient is lower in the mantle
       • Radioactive heat production is concentrate within the crust
       • The mechanism of thermal transport changes form conduction within the rigid lithosphere plates, to convection in the asthenosphere and the upper mantle, and this transports the heat differently
   • Volcanoes bring magma form depth
   • Mines and Boreholes
   • Ophiolite suites-ocean crust on land
     • During the collision of plates, sections of oceanic crust may be broken off a descending oceanic plate and thrust onto the edge of the continental plat, instead of being carried down into the mantle
       • They may be exposed to erosion

2. Indirect

   • Seismic waves
     • P and S waves are seismic waves that travel through the layers of the earth
       • body waves
         • faster if the rock becomes more rigid and more incompressible
         • slower if the rock becomes more dense
   • The shadow zone
     • Where P and S waves cannot pass
       • Seismic waves are refracted at the Gutenberg discontinuity
   • Density
   • Meteorites