Which information is needed to construct a geomagnetic time scale?

the magnetic direction of rocks along the surface of Earth and the age of rocks along the surface of Earth

Explanation:

The earth's magnetic field or geomagnetic field is believed to originate from the movement of molten iron and nickel in the outer core.

During a period in which the earth magnetic field is normal, crystallising magnetic minerals in magma records the orientation of the prevailing geomagnetic field. At other times when the field reverses and the magnetic field orientation changes, magnetic minerals in cooling magma stores this record.

To create a geomagnetic time scale, geologists can assign absolute ages to the records of these paleomagnetic anomalies which are the reversals. The rock is dated using radiometric techniques and each period of reversal is ascribed an absolute geologic age. Therefore, the magnetic direction of rocks along the surface of Earth and the age of rocks along the surface of Earth helps to build the geomagnetic time scale of the earth.

the answers are a and c