Which term describes the movement of carbon through living organisms, air, water, and rocks?

• A. Oxygen cycle
• B. Nitrogen cycle
• C. Hydrologic cycle
• D. Carbon cycle

Answer: (D)

Carbon moving through living things, air, water, and rocks is described by the carbon cycle. Plants take in carbon dioxide from the air during photosynthesis and convert it into sugars that feed growth. Animals obtain carbon by eating plants and other organisms, and they release carbon back into the environment through respiration, waste, and decay. When organisms die, decomposers break down their bodies, returning carbon to the soil and releasing some back to the air. The oceans play a big role too: CO2 dissolves in seawater and becomes part of marine life and carbonate minerals, and some carbon is stored in deep waters. Over long timescales, carbon becomes locked in rocks and fossil fuels; weathering and geological processes slowly release some of this carbon back into air or water. Human activities, like burning fossil fuels and deforestation, increase the movement of carbon and change how much CO2 is in the atmosphere. All these exchanges keep carbon cycling through living things, air, water, and rocks, which is why this is called the carbon cycle.