Tiny Magnetic Fossils Suggest an Ancient 'GPS' Inside a Lost Sea Creature

Tiny magnetic fossils point to an internal navigation system in an ancient marine animal

Microscopic magnetite grains recovered from North Atlantic seafloor sediments may be the fossilized remnants of an internal "GPS" that once helped an ancient marine organism navigate long distances using Earth's magnetic field, researchers say.

The particles are extremely small — roughly 50 times narrower than a human hair — and are composed of strongly magnetic iron oxide (magnetite). Similar grains have been found in sediments as old as about 97 million years, though debate has persisted over whether they formed biologically or through inorganic processes.

In the new study, scientists used high-resolution three-dimensional imaging to examine the magnetic structure of one cone-shaped magnetite grain dated to about 56 million years ago. Inside the particle they identified a closed loop of magnetization resembling a vortex, an internal arrangement that would be especially sensitive to both the direction and the local strength of Earth's magnetic field.

"We show that the large magnetization means it would be optimized to detect variations in the strength of Earth's magnetic field from location to location, which is a key part of building a natural 'GPS system,' enabling an animal to actually geolocate itself, not just know, for instance, which way is north," said Rich Harrison, professor of Earth and planetary materials at the University of Cambridge and co-leader of the study published in Communications Earth & Environment.

Earth's magnetic field is generated by the motion of molten iron in the planet's outer core and extends far into space. Many migrating animals — including birds, fish and insects — are thought to use magnetic cues for orientation, but the biological mechanism for sensing those cues remains uncertain. One longstanding hypothesis is that magnetite particles inside tissues act like tiny compass needles.

Identifying the organism that produced the fossil grains is difficult because the particles were not found alongside other bodily remains. The researchers say a widespread migratory species would be a plausible source because it could leave abundant fossil traces; eels are mentioned as one candidate due to their long trans-Atlantic migrations. Alternatively, the magnetite could have come from magnetotactic microbes that build chains of magnetite crystals called magnetosomes — though typical magnetosomes are about 20 times smaller than the fossils studied here.

"There is strong evidence suggesting that many other organisms — including mammals, birds, amphibians, reptiles and insects — do have magnetic-navigation capabilities. What remains unknown is how they do it," said study co-leader Sergio Valencia, a physicist at Helmholtz-Zentrum Berlin. "If these particles were connected to magnetoreceptive cells, their reorientation in Earth's field could produce mechanical or electrical signals the organism's nervous system could interpret."

The study strengthens the case that some ancient organisms may have carried highly optimized magnetic sensors capable of detecting not only direction but also variations in field intensity — a capability that could allow true geolocation rather than simple compass-like orientation.

Reporting: Will Dunham in Washington. Editing: Daniel Wallis. Study published in Communications Earth & Environment.