Explain the various forms in which carbon is found on the earth.

Explanation

### Step-by-Step Solution:

1. **Elemental Form of Carbon**:
- Carbon can be found in its elemental form, primarily as two allotropes: diamond and graphite.
- **Diamond**: A crystalline form of carbon, known for its hardness and brilliance.
- **Graphite**: A softer form of carbon that is used in pencils and as a lubricant.

2. **Combined State of Carbon**:
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