To construct a geomagnetic time scale, the two correct answers are:
- The age of the rocks along the surface of the Earth.
- The magnetic direction of rocks along the surface of Earth.
These two pieces of information are essential for understanding the history of Earth's magnetic field and how it has changed over time. The age of the rocks helps to date the magnetic reversals, while the magnetic direction of the rocks provides data on the orientation of the magnetic field at those times.