- Clay
- Cloud Seeding
- Clouds and Cloud Types
- Coal
- Comets
- Condensation
- Continental Divide
- Continental Drift Theory
- Continental Shelf
- Convection (Updrafts and Down-drafts)
- Convergent Plate Boundary
- Cook, James (1728-1779)
- Copernicus, Nicolas (1473-1543)
- Coral Reefs and Corals
- Coriolis Effect
- Coronal Ejections and Magnetic Storms
- Correlation (Geology)
- Corrosion
- Cosmic Microwave Background Radiation
- Cosmic Ray
- Cosmology
- Country Rock
- Cousteau, Jacques-Yves (1910-1997)
- Crater, Volcanic
- Craton
- Creep
- Cretaceous Period
- Cross Cutting
- Crust
- Crutzen, Paul J. (1933- )
