Final answer:
The correct sentence completion is: Most carbon is stored in rocks and sediments, while the rest is stored in the ocean, fossil fuels, and living organisms. The atmosphere also plays a crucial role in the carbon cycle as a significant carbon dioxide reservoir.
Step-by-step explanation:
Most carbon is stored in rocks and sediments, while the rest is stored in the ocean, fossil fuels, and living organisms. Specifically, the atmosphere is also a significant reservoir where carbon dioxide is essential to life on Earth. Sedimentary rocks, ocean sediments, and soils serve as long-term storage, while living organisms cycle carbon quickly through the processes of photosynthesis and respiration.
Fossil fuels, formed from the anaerobically decomposed remains of ancient plants and algae, are a major carbon reservoir, yet they are a non-renewable resource due to their slow formation rate compared to their current exploitation rate. Carbon can also enter the atmosphere through geological activities such as volcanic eruptions. Overall, the biogeochemical carbon cycle involves complex movement through various reservoirs, including land, water, and air.