Geomagnetic dating of rocks is possible because

Thus, magnetostratigraphy no longer represents a dating tool based only on the geomagnetic polarity reversals, but comprises a set of techniques that includes measurements of all geomagnetic field parameters, environmental magnetism, rock magnetic and palaeoclimatic change recorded in sedimentary rocks, and key corrections to magnetic directions related to geodynamics, tectonics and diagenetic processes.Over the past century numerous methodologies have been developed to detect time variations of the geomagnetic field and environmentally significant magnetic properties in rocks.Profound erosion subsequently destroyed much of the volcano, leaving only peripheral steep-sided massifs.Lavas of the Younger Volcanic Series were erupted from about 3.5 m.y. ago, flooding the denuded stumps of the shield volcano.The mean directions of magnetization of the three groups of lavas are not significantly different from one another and are close to an axial dipole direction.The combined paleomagnetic and dating studies on the lavas also yield further information on the geomagnetic polarity time scale; 16 results on rocks with ages lying between 3.5 and 0.17 m.y.

A common problem with any dating method is that a sample may be contaminated with older or younger material and give a false age.

Sedimentary rocks are rarely useful for dating because they are made up of bits of older rocks.

Uranium is present in many different rocks and minerals, usually in the form of uranium-238.

study of the intensity and orientation of the earth's magnetic field as preserved in the magnetic orientation of certain minerals found in rocks formed throughout geologic time.

Paleomagnetic studies of rocks and ocean sediment have demonstrated that the orientation of the earth's magnetic field has frequently alternated over geologic time.