Final answer:
Geologists use magnetic reversal to build a magnetic time scale called the Geomagnetic Polarity Time Scale (GPTS) by studying the magnetic properties of rocks and sediments.
Step-by-step explanation:
Geologists use magnetic reversal to build a magnetic time scale called the Geomagnetic Polarity Time Scale (GPTS). Magnetic reversals are a natural process on Earth where the magnetic north pole moves to the geographic south pole. By studying the magnetic properties of rocks and sediments, geologists can determine the age of these deposits and establish a timeline of Earth's magnetic field changes over time. This helps in understanding the history of the planet and can be used for relative and absolute dating of geological events.