They needed to measure the times of the reversals so that any point in the characteristic pattern could be assigned an absolute age. The same pattern seen in space on the ocean floor was seen in age as determined from the rocks on land. Increasing pressure makes it harder for rocks to undergo fracture or frictional sliding on faults. Thus as depth in the earth increases, and thus pressure increases, fracture and faulting become harder and harder. This makes fracture and friction more likely to occur near the surface.
Temperature has little effect on fracture and friction.
Increasing temperature makes it easier for rocks to deform by flow, and pressure has little effect. At a given depth, the process that is easier to occur is the one that will occur. Thus, near the surface where the temperature and pressure are both low, flow is hard, but fracture and friction is easy. Fracture and friction result in earthquakes. At greater depth, the pressure is too high for fracture and friction to occur easily, and the temperature is high so flow can occur more easily.