Overview
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  Spheres of B. Cycles
  Nitrogen Properties
  Simple Nitrogen Cycle
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  Spheres of the N Cycle
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Mantle

The main bulk of the Earth, between the crust and the core, ranging from depths of about 40 to 2900 kilometers. It is composed of dense silicate minerals rich in iron and magnesium and divided into concentric layers by phase changes that are caused by the increase in pressure with depth.

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