How do magnetic stripes on the ocean floor record reversals of Earth’s magnetic field?

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Grand Canyon rock layering — geochronology The steep walls of the Grand Canyon contain a number of layers of sedimentary rock laid down over millions of years. The lower formations belong to the early Precambrian age, while the upper layers are of the Paleozoic age. The line between the two sets of formations is called the Great Unconformity.

Magnetic stripes on the ocean floor serve as a permanent record of Earth’s magnetic field reversals due to the process of seafloor spreading. As new oceanic crust forms at spreading centres, molten rock cools and solidifies. During this cooling process, iron-titanium oxide minerals within the crust undergo thermoremanent magnetization, effectively "locking in" the orientation of the ambient magnetic field at that time.1

When Earth’s magnetic field undergoes a geomagnetic reversal, the polarity of the newly forming crust is oriented in the opposite direction. As the crustal plates move away from the ridge, they carry this magnetic signature with them, creating a symmetrical pattern of "normal" and "reversed" polarity stripes on either side of the ridge.1

Positive anomalies occur where the crust is magnetized parallel to the current field, while negative anomalies represent reversely magnetized crust. By correlating these stripes with known time scales of magnetic reversals, scientists can determine the age of the ocean crust and calculate the rate of seafloor spreading.1