To construct a geomagnetic time scale, the two correct answers are:
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The magnetic direction of rocks along the surface of Earth - This information is crucial as it helps to identify the orientation of the Earth's magnetic field at various points in geological time, which is fundamental in creating a geomagnetic time scale.
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The age of rocks along the surface of Earth - Knowing the age of the rocks allows scientists to correlate the magnetic directions with specific time periods, creating a timeline of geomagnetic reversals and other changes.
The other options (average speed of tectonic plates and the length of the mid-oceanic ridge) are not directly necessary for constructing a geomagnetic time scale.