“What happened here is that these rocks were struck by lightning sometime between when they were formed many thousands of years ago, and when they were carved,” Fu said. “Because lightning is an electric current, it produces very strong magnetic fields, many orders of magnitude stronger than normal … and we believe the ancient Mesoamerican people were able to detect these anomalies.”

It’s uncertain exactly how they detected the anomalies, but earlier research had turned up evidence that Mesoamericans may have used lodestones — naturally magnetized rocks — for a variety of purposes.

“In one case, in 1975, people discovered a hematite-rich bar,” Fu said. “Its purpose was unknown, and it was broken, but it was clearly very carefully made.

“If you were to tie it on a string or float it on a piece of wood, it actually could act as a compass needle,” he added. “If the makers of these sculptures had access to a tool like that, that’s one way they could have detected them.”

And though the study suggests that ancient Mesoamerican people had knowledge of magnetism and how to detect it, it leaves unanswered the question of why the figures were carved to highlight their magnetism.

“The short answer is we don’t have a good idea for the exact reason they did this,” Fu said. “There are some hypotheses which are quite intriguing … that involve digging into why we think people made these sculptures.

“Probably the most successful idea is that they might represent some depiction of the ancestors of the ruling elites,” he continued. “The idea is: If you have some claim to power, sculptures of your ancestors with strong magnetic anomalies could appear very impressive to your subjects. The word people use in the literature is that there’s a performative aspect to these sculptures, so when the sculptures deflected a magnetized stone, it would appear as though there was something alive with it, or some supernatural aspect to it.”

Ultimately, Fu said, the study offers key evidence that an understanding of magnetism existed in the Americas far earlier than first believed.

“In the Old World, there was some documentation of magnetism in the Greek world by the sixth century B.C., and the first usable compass wasn’t until centuries later in China,” he said. “To me, what’s really interesting is this is a completely independent discovery. There’s a perception that the Old World is the advanced world and transferred all this knowledge to the New one, but we are realizing that they knew a lot, and I think this is one more piece of evidence for that.”

This research was supported with funding from NASA.