Final answer:
The total amount of carbon in the Earth-atmosphere system remains constant due to its cyclical nature through various parts of the Earth: D. It remains constant because carbon cycles through different parts. This biogeochemical cycle includes the process of photosynthesis and respiration, as well as changes from volcanic activity and human emissions.
Step-by-step explanation:
The total amount of carbon in the system made up of Earth and its atmosphere remains relatively constant because carbon cycles through different parts of the Earth, such as the atmosphere, hydrosphere, biosphere, and geosphere. The correct answer to the student's question is D. It remains constant because carbon cycles through the atmosphere, hydrosphere, biosphere, and geosphere. Processes such as photosynthesis and respiration are part of this cycle. Photosynthesis converts carbon dioxide gas to organic carbon, while respiration turns organic carbon back into carbon dioxide gas. Moreover, natural phenomena such as volcanic activity and human-induced emissions can also influence the carbon cycle by adding or removing carbon dioxide from the atmosphere.
The biogeochemical carbon cycle involves movement and storage of carbon in various forms across different carbon reservoirs including the atmosphere, the oceans, soil, and biological matter. Long-term carbon storage occurs when organic material is buried underground and becomes fossilized, and this stored carbon may re-enter the cycle through volcanic activity or human emissions.