About every 2 million years is the earths magnetic field change direction. Hence, option B is correct.
What is earths magnetic field?
The Earth's field fluctuates between 25 and 65 T. In contrast, a strong refrigerator magnet has a field of about 10,000 T. (100 G). A graphic showing intensity contours is referred to as a "isodynamic chart." The World Magnetic Model shows that the intensity tends to decrease from the poles to the equator.
On Earth, the movement of liquid metal in the planet's outer core generates electric currents. Due to Earth's rotation on its axis, these electric currents combine to form a magnetic field that envelops the entire planet. The magnetic field is essential to the survival of life on Earth.
Thus, option B is correct.
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