Ancient sea creatures may have navigated using Earth's magnetic field

Ancient sea creatures may have navigated using Earth's magnetic field
by Robert Schreiber
Berlin, Germany (SPX) Oct 21, 2025

Some of the earliest marine organisms may have possessed a natural compass that helped them find their way through ancient oceans, according to a new study led by researchers from the Helmholtz Centre for Materials and Energy (HZB). Using cutting-edge X-ray techniques, scientists have shown that certain fossilized magnetic particles-known as "giant magnetofossils"-were ideally structured for detecting subtle variations in Earth's magnetic field, suggesting they once enabled biological navigation.

These magnetite particles, first discovered in marine sediments a few years ago, are about 10 to 20 times larger than the magnetite crystals typically produced by modern magnetotactic bacteria. They appear in distinctive needle, spindle, bullet, and spearhead shapes. The organisms that created them remain unknown, and their function has been debated: while some researchers proposed they served as hard, protective armor, others have suggested they were part of a magnetosensory system.

To test that possibility, physicist Sergio Valencia of HZB and palaeomagnetism expert Richard J. Harrison of the University of Cambridge examined a spearhead-shaped magnetite fossil measuring roughly 1.1 micrometers wide and 2.25 micrometers long. The sample, collected from 56-million-year-old North Atlantic sediment, was analyzed at the Diamond Light Source in Oxford using a non-destructive X-ray magnetic imaging technique developed by Claire Donnelly at the Max Planck Institute for Chemical Physics of Solids in Dresden.

This advanced approach-known as pre-edge phase X-ray magnetic circular dichroism (XMCD) ptychography-allowed the team to reconstruct the internal magnetic domain structure in three dimensions with a resolution of just tens of nanometers. "With the help of magnetic vector tomography, all three components of magnetization could be spatially resolved throughout the grain," said Valencia. "Once the new BESSY III source is operational, similar studies will be possible in Berlin."

The 3D images revealed a single, stable magnetic vortex inside the fossilized crystal. The researchers calculated that this vortex could have responded to tiny fluctuations in the magnetic field with strong forces-precise enough to let an organism detect both field strength and direction. "Marine organisms, for example a fish, may have used this property for magnetic navigation," said Harrison. Even if the particles originally evolved as physical protection, their descendants may have adapted them for magnetoreception over evolutionary time.

Magnetoreception is widespread today, known in species from molluscs and fish to birds and mammals. The discovery of giant magnetofossils dating back up to 97 million years indicates that sensitivity to magnetic intensity-and possibly true magnetic navigation-originated far earlier than previously confirmed.

The findings also have implications beyond Earth. Iron-oxide particles resembling bacterial magnetite have been detected in the Martian meteorite ALH84001. "We now have a method to determine whether any magnetite particles found in Mars samples are truly biological," said Valencia. "It could help identify signatures of past life on other planets."

Research Report:Magnetic vector tomography reveals giant magnetofossils are optimised for magnetointensity reception