On February 1976 archaeologists found a sculpted turtle head with magnetic properties in the ceremonial center of Izapa in the coastal plain of the State of Chiapas in Mexico. Radiocarbon dating gave that sculpture the date of 1500 BC.
About 150 km to the southeast, in the ancient ceremonial center of Monte Alto in Guatemala, were later found much more primitive sculptures that can be dated accurately to 2000 BC. They are the famous stone heads and potbellies, belonging to the culture of Monte Alto, one of the oldest in Mesoamerica and probably predating the Olmec culture.
During the investigations on 1979 it was discovered that many of the sculptures from Monte Alto were magnetic. To the extent that certain distinctive patterns of magnetism are repeated with some frequency, it appeared that the sculptures were created by craftsmen who were familiar with these properties. If so, the Monte Alto sculptures should be recognized as the oldest known magnetic artifacts in the world.
Since both heads and bodies are rather roughly shaped from large rounded basaltic blocks, the subjects have a stout appearance. That’s why they’ve been called potbellies. Of the collection of potbellies on display in the municipal park of La Democracia, Guatemala and in front of the local museum, four of the stone heads and three of the bodies have magnetic properties.
The four stone heads have a north magnetic pole located on their right temples, while three of them have south magnetic poles below the right ear, and the fourth (the one in front of the museum) has a south magnetic pole on its left temple. According to the researchers it is unlikely that such a pattern is due to chance.
Of the three potbellies, two have their magnetic north and south poles located less than 10 centimeters from each other, near the navel (specifically, between the fingertips that embrace the more rounded parts of the abdomen). The third has its north magnetic pole located at the back of the neck.
The similarity of the locations of the magnetic poles suggested that the sculptors were aware of their presence.
A study published by researchers from Harvard and Yale Universities, the California Institute of Technology and the National Institute of Seismology, Volcanology, Meteorology and Hydrology of Guatemala in 2019, confirmed that the apparently intentional coincidence of carved anatomical features and pre-existing magnetized regions implies that the sculptors were able to detect the presence of magnetic fields in the rocks.
Magnetometers were used to map the distribution of magnetization in eleven of the Monte Alto potbellies. The results revealed, for the first time, that the sculptures were originally magnetized by lightning strikes before the carving process, and that the correspondence between the magnetic anomalies of the sculptures and the sculpted anatomical features is not random. This is consistent with the conclusions of the 1976 study.
According to the researchers, this evidence reinforces the understanding of the knowledge of magnetism in pre-Hispanic Mesoamerica.
Sources: Knowledge of magnetism in ancient Mesoamerica: Precision measurements of the potbelly sculptures from Monte Alto, Guatemala, Roger R.Fu, Joseph L. Kirschvink, Nicholas Carter, Oswaldo Chinchilla Mazariegos, Gustavo Chigna, Garima Gupta, Michael Grappone. Journal of Archaeological Science, volume 106, June 2019, pp.29-36, doi.org/10.1016/j.jas.2019.03.001 / Pre-Columbian Magnetic Sculptures in Western Guatemala (Paul A. Dunn and Vincent H. Malmström, 1979).