Assertion :- The geologcial histroy of earth closely correlates with the biological history of earth.
Reason :- Earth is very old.

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion.
B. If both Assertion & Reason are True but Reason is a not a correct explanation of the Assertion.
C. If Assertion is True but the Reason is False.
D. If both Assertion & Reason are false.

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that the geological history of Earth closely correlates with its biological history. This means that the changes in the Earth's physical structure and environment (geological history) are linked to the evolution and development of life forms (biological history).

2. **Understanding the Reason**:
- The reason given is that Earth is very old. This implies that the extensive time span of Earth's existence allows for significant geological changes and the evolution of diverse life forms.

3. **Exploring Geological History**:
- Geological history refers to the changes in the Earth's atmosphere, oceans, continents, and biosphere over time. For example, the formation of oceans, the development of landmasses, and fluctuations in temperature are all part of this history.

4. **Exploring Biological History**:
- Biological history involves the evolution of organisms over time, starting from simple life forms like blue-green algae to more complex organisms such as mammals and eventually humans. This evolution occurred alongside the geological changes on Earth.

5. **Correlation Between Geological and Biological History**:
- Both histories are interlinked. As the Earth underwent geological changes, these changes created new environments that influenced the evolution of life. For instance, the increase in atmospheric oxygen allowed for the development of more complex life forms.

6. **Conclusion**:
- Since both the assertion and the reason are true, and the reason explains the assertion, we conclude that the correct answer is that both the assertion and reason are true, and the reason is a correct explanation of the assertion.

### Final Answer:
Both assertion and reason are true, and the reason is a correct explanation of the assertion.