Earth’s magnetic field is treated as a stable global system that maintains a consistent dipole structure aligned with the planet’s rotation. That structure produces a north and south magnetic pole and acts as a barrier against charged particles from the Sun and beyond. The field is generated deep within the planet by the motion of liquid metal in the outer core, where convection drives electric currents that sustain the geodynamo. Modern measurements show variation over time, including reversals, but the overall structure remains coherent and predictable.
Rock formations in present-day Morocco preserve a different state of this system. Volcanic and sedimentary layers formed during the late Ediacaran period, approximately 568 to 562 million years ago, contain magnetic signatures locked in at the time of their formation. These signatures record the direction of Earth’s magnetic field at specific moments, creating a sequence of measurements across stacked layers of rock. The sequence is continuous enough to track changes in the magnetic field through time.
The recorded directions change rapidly between layers. When those changes are converted into rates, they approach values on the order of one hundred degrees per million years. Plate tectonics cannot produce that level of change. The movement of continents operates on far slower timescales. Even extreme cases of polar motion remain within known physical limits that fall well below the rates recorded in these rocks. The source of the change is not the movement of the crust or the rotation of the outer shell relative to the spin axis.
The variation originates within the magnetic field itself. The data show that the field shifted direction repeatedly over short intervals. Magnetic inclinations change from shallow to steep within stratigraphically constrained units. Transitional directions appear between opposing polarities. When plotted, the data do not cluster around a stable axis. They form elongated distributions that reflect continuous reorientation rather than isolated reversals.
The rock record includes both volcanic and sedimentary units, which capture the magnetic field in different ways. Volcanic rocks acquire magnetization as they cool, locking in the direction of the field at that specific moment. Each flow or eruption provides a discrete snapshot. Sedimentary rocks acquire magnetization more gradually during deposition and early diagenesis. That process averages out short-term fluctuations and preserves a longer-term signal.
The volcanic sequences in Morocco show highly variable magnetic directions across successive units. The sedimentary layers within the same sequence preserve a more stable average direction with a high inclination. The two datasets overlap in their broader alignment while differing in their short-term behavior. This combination shows that the underlying dipole component remained present while strong directional variability occurred on shorter timescales.
Precise dating of the volcanic units constrains the timing of these changes. Zircon crystals extracted from the rocks provide uranium-lead ages that define the sequence between roughly 567.9 million years and 562.2 million years. The changes in magnetic direction occur within that interval. The stratigraphic order of the layers matches the sequence of magnetic shifts, confirming that the variation is primary and not the result of later alteration.
The rates derived from these data exceed the limits of both plate motion and polar reorientation. The values are consistent with rapid variation in the geodynamo itself. Fluid motion within the outer core can change on timescales shorter than those governing large-scale solid Earth processes. The magnetic field generated by that motion can respond accordingly. The record in these rocks reflects that behavior.
Additional features in the same sequence provide independent constraints on the position of the region during this time. Striated and grooved surfaces preserved within the layers indicate glacial activity. These features form when ice moves across rock surfaces, carving linear marks aligned with the direction of motion. Their presence shows that the region was positioned at high latitude during the time the rocks formed. The magnetic data therefore record field behavior while the geographic position remained consistent.
The combination of high-latitude indicators and rapidly changing magnetic directions removes the need to invoke large-scale movement of the crust. The changes do not represent continents moving across the globe. They represent a magnetic field that did not maintain a fixed orientation.
Measurements of field strength from other Ediacaran rocks indicate lower intensity compared to later periods. A weaker magnetic field produces less deflection of charged particles entering the upper atmosphere. The degree of shielding depends on field strength and structure. A reduction in intensity allows more particles to reach lower altitudes. The Moroccan data show that directional instability occurred during a time when field strength was also reduced.
The magnetic record from this interval is not limited to a single location. Similar patterns of directional variability appear in rocks of comparable age from other regions, including Laurentia. In those datasets, magnetic directions also form elongated distributions rather than tight clusters. When treated using statistical methods appropriate for non-symmetric distributions, the results align with the patterns observed in Morocco. The consistency across regions indicates that the behavior is global in scale.
The data require a model in which the time-averaged dipole remains aligned with the rotation axis, while short-term variability produces large directional shifts. This behavior can be described as enhanced secular variation within the geodynamo. The variability is directional and structured rather than random. It follows preferred orientations that produce elongated patterns in the data.
One explanation for this behavior involves the internal state of the core during this period. Models of core evolution allow for changes in heat flow and composition over geological time. These changes affect the pattern of convection within the outer core. Variations in convection alter the structure of the magnetic field generated by the geodynamo. The Ediacaran interval may represent a state in which those conditions produced increased variability and reduced stability.
The Moroccan sequence provides a continuous record of that state. The stratigraphy preserves successive magnetic directions within a well-defined time window. The data show rapid shifts, transitional states, and sustained variability across multiple layers. The sedimentary and volcanic records together define both the short-term changes and the longer-term average.
This record establishes that the magnetic field did not maintain a stable dipole orientation during this interval. The behavior differs from the present-day field, where directional changes occur but remain centered around a consistent axis over comparable timescales. The Ediacaran field shows repeated deviation from that axis within a constrained sequence of rock layers.
The preserved data define a period of rapid magnetic reversals, directional instability, and reduced field strength. The sequence is ordered, dated, and consistent across multiple units and locations. The changes occur within a defined interval and are recorded directly in the geological record.
Source:
Pierce, J. S., Evans, D. A. D., Polomski, D. E., et al. (2025). Magnetostratigraphic constraints on the late Ediacaran paleomagnetic enigma. Science Advances, 11(40), eady3258.
https://www.science.org/doi/10.1126/sciadv.ady3258
