Essential life materials, like nitrogen and carbon, are exchanged and recycled through
biogeochemical cycles
earth's core
volcanic activity
convection and condensation

The answer is A, biogeochemical cycles.

Biogeochemical Cycles.  

Explanation:

In Earth Science and ecology, a biogeochemical cycle or cycling of substances refers to a pathway by which a chemical component mediates via biosphere (biotic) and lithosphere, atmosphere, and hydrosphere (abiotic) constituents of the Earth.  

There are biogeochemical cycles for the chemical elements carbon, mercury, calcium, hydrogen, phosphorus, nitrogen, sulfur, selenium, and oxygen. The important life constituents, like carbon and nitrogen, are recycled and exchanged via biogeochemical cycles.  

chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. these processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. understanding chemical changes is a major part of the science of chemistry.