It is a common notion that the earth's magne tism is due to the

Options

A. presence of a huge permanent magnet in the interior of the earth
B. presence of electric currents circulating in the interior of the earth
C. influence of the sun's magnetic field
D. influence of a nuclear explosion

Answer

### Step-by-Step Solution:

1. **Understanding Earth's Magnetism**:
- The first step is to recognize that there are various theories regarding the source of Earth's magnetism. A common misconception is that there is a permanent magnet inside the Earth.

2. **Evaluating the Permanent Magnet Theory**:
- The idea that a huge permanent magnet exists in the Earth's interior is incorrect. The Earth consists mainly of molten substances, and there is no solid permanent magnet present.

3. **Considering Electric Currents**:
- The correct explanation for Earth's magnetism lies in the presence of electric currents. The molten iron and nickel in the Earth's outer core move due to convection currents.

4. **Understanding Convection Currents**:
- As the molten iron and nickel circulate in the outer core, they generate convection currents. These currents are responsible for creating a magnetic field around the Earth.

5. **Eliminating Other Theories**:
- The influence of the Sun's magnetic field and nuclear explosions are also proposed theories but are incorrect. The Sun's magnetic field does not significantly influence Earth's magnetism, and nuclear explosions do not play a role in generating the Earth's magnetic field.

6. **Conclusion**:
- Therefore, the correct explanation for Earth's magnetism is the presence of electric currents circulating in the molten iron and nickel in the outer core.

### Final Answer:
The Earth's magnetism is primarily due to the presence of electric currents circulating in the molten iron and nickel in its outer core.

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