According to the law of conservation of mass, the mass of a closed system will remain constant over time. In other words; mass can neither be created nor destroyed, it can only be rearranged in space. Also, the First Law of Thermodynamics states that energy can neither be created nor destroyed only transformed from one form to another. With Earth being virtually a closed system, all mass and energy on Earth must rearrange itself. This is done by cycling through the various spheres.
The cycling of nutrients is more than just an explanation for where mass comes from and where it goes, it is the conduit by which all life on Earth receives its nutrition. As the nutrients cycle through the various reservoirs they change from inorganic to organic molecules, due to redox reactions, making them useful to living organisms
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