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.  

metric time was an attempt to create a standard unit of time based off of 10, but it never took off an is not included in the metric system (si)

sup bro, im dumb, but this is what i found xd

"the ozone layer acts as a filter for the shorter wavelength and highly hazardous ultraviolet radiation (uvr) from the sun, protecting life on earth from its potentially harmful effects. when the sky is clear, there is an inverse relationship between stratospheric ozone and solar uvr measured at the earth's surface"