Flexi Says: Scientists use paleomagnetic measurements of iron-rich rocks in the rock record to study the history of Earth's magnetic field changes. Specialized instruments such as magnetometer and multi-sensor whole core logger system are used for paleomagnetic measurements. These measurements provide evidence of the intensity and direction of the magnetic field at the time of the rock formation. There are two main fields in paleomagnetism. "Geomagnetic secular variation" records changes in the direction and intensity of Earth's magnetic field. "Magnetostratigraphy" is helpful in determining the age of rocks by understanding the polarity reversal history of Earth's magnetic field.