Carbon Dioxide is being added to the cycling pool by

Options

A. respiration and combustion
B. sedimentation of carbonates
C. precipitation, skeltons and fossilisation
D. Both B and C

Answer

### Step-by-Step Solution:

1. **Understanding the Cycling Pool**:
- The cycling pool refers to the nutrient cycle, specifically focusing on how carbon is cycled through various processes in the environment.

2. **Processes Contributing to Carbon Dioxide Addition**:
- Carbon dioxide is added to the cycling pool through several key processes:
- **Sedimentation of Carbonates**: This involves the deposition of calcium carbonate (CaCO3) in oceans and the earth's crust. Over time, this sedimentation contributes to the carbon pool.
- **Precipitation**: This refers to the process of rain, which can also lead to the dissolution of carbonates and the release of carbon dioxide into the environment.
- **Skeleton Formation**: Organisms, particularly marine organisms, have skeletons made of minerals, predominantly carbon. When these organisms die, their skeletons contribute carbon to the soil, enriching the cycling pool.
- **Fossilization**: After organisms decay, their remains can fossilize, which also contributes carbon back into the soil and the cycling pool.

3. **Conclusion**:
- Therefore, carbon dioxide is added to the cycling pool through the processes of sedimentation of carbonates, precipitation, and the contribution from skeletons and fossilization. The answer to the question is both B (Skeletons) and C (Fossilization).