Applying the principle of cross-cutting relationships, this fault that offsets the layers of rock must have occurred after the strata were deposited. Dinosaurs and the History of Life. These changes typically occur so slowly that they are barely detectable over the span of a human life, yet even at this instant, the Earth's surface is moving and changing. Changes in the earth's magnetic field from normal polarity to reversed polarity or vice versa. This change is called radioactive decay. The law of included fragments is a method of relative dating in geology.
Every reversal looks the same in the rock record, so other lines of evidence are needed to correlate the site to the GPTS.
Dating Rocks and Fossils Using Geologic Methods
University of California Press While digging the Somerset Coal Canal in southwest England, he found that fossils were always in the same order in the rock layers. Geologists also use other methods - such as electron spin resonance and thermoluminescencewhich assess the effects of radioactivity on the accumulation of electrons in imperfections, or "traps," in the crystal structure of a mineral - to determine the age of the rocks or fossils.