What Is Paleomagnetism?

Scientists can study the history of Earth’s magnetic field by using Earth’s rocks as records. Paleomagnetism is the study of magnetic rocks and sediments to record the history of the magnetic field. Some rocks and materials contain minerals that respond to the magnetic field. So, when rocks form, the minerals align with the magnetic field preserving its position. It’s called rock magnetism when rocks record the position of the magnetic field. The magnetic signature of the rocks allows paleomagnetists to date the rocks and map the position of the field at the time of their formation.

Why Is This Important?

Piecing together the history of Earth’s magnetic field helps us predict its future behavior. We know from records preserved in rock that Earth’s magnetic field has flipped and reversed in the past. Based on magnetic records, we know the last magnetic pole shift occurred 781,000 years ago. Earth’s magnetic field also fluctuates in strength every once in a while due to changes in temperature and convection currents at the core. Paleomagnetism also provides evidence to support theories in plate tectonics. Because the ocean floor is mostly composed of basalt, an iron-rich substance containing minerals that align with the magnetic field, they record the alignment of the magnetic fields surrounding oceanic ridges. Scientists studied the magnetic signatures of the rocks on the ocean floor and noticed some recorded opposite directions for magnetic field lines even though they were side by side. This likely occurred because magma rose from the ridges in the ocean floor and formed new rock recording a more recent alignment of the magnetic field while pushing old rock with more outdated magnetic records further from the ridge. We have already learned so much about our planet by studying the history of Earth’s magnetic field through natural rock magnetism. And as paleomagnetists gather more information, we can continue to learn more about the planet’s history. A more detailed record of Earth’s magnetic past will provide answers regarding the formation of the continents as well as the behavior of our magnetic field.