A laboratory with its own magnetism

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Ariana Fernandez and her magnetometer have a breathtaking view of Peru.

Admittedly, this is not a postcard image. Fernandez, a senior specializing in archaeological studies, is more interested in soil samples than in panoramic views. Yet with her scorched pieces of earth and world-class technology, she sees South America’s past, present, and geophysical future in stunning detail.

“I help people learn more about societies from the past, while also filling the scientific part of my brain,” Fernandez said, clutching a handful of soil sample cubes on the way to the lab. “What I didn’t expect was that I would create a magnetic dating curve for all of Peru.”

His is just one of the research stories unfolding in the Yale Archaeomagnetism Lab. Located in a renovated rectory on Hillhouse Avenue, the modest lab uses cutting-edge magnetic dating techniques for the research projects of the university’s archaeologists, geophysicists and anthropologists.

“It went on for years,” said Roderick McIntosh, professor of anthropology and curator of anthropology at the Yale Peabody Museum of Natural History. “It is the only laboratory in the world dedicated to archaeomagnetism.

Here’s what it means: If a rock, clay, or mineral containing iron ore is heated enough and then cooled, it maintains a specific magnetism, called thermal remanent magnetism. Analysis of the material reveals both the direction and the intensity of this magnetism.

Scientists are able to compare this information with changes in Earth’s magnetic field over time, setting a date for the cooling event that is accurate to less than 11 years. Archaeologists, who often study dynamic civilizations that developed or changed rapidly, have long sought such precision. Radiocarbon dating, by comparison, is only accurate within 50-100 years.

Man-drawn artifacts

The Yale lab opened in 2013. It is part of a complex of small labs built over the past decade under the auspices of Yale University Archaeological Laboratories (YUAL) and the Yale Study Center. ancient Yale pyrotechnics. The center also has laboratories dedicated to archaeometallurgy and archaeohistology.

“Of all the ways that humans have used fire to make things or to alter their environment, this is what we are studying,” McIntosh explained.

To conduct research on archaeomagnetism, Yale needed to cover a room with several layers of steel to protect it from external magnetic influences. There was only one person in the United States familiar with such a construction, a geophysicist from California, and the university brought him to New Haven to build the facility.

The basement laboratory is equipped with complete archaeomagnetism equipment: a fluxgate magnetometer, to measure the magnetization values; a thermal demagnetizer, to prepare samples for measuring intensity; an alternating field demagnetizer, to remove the most recent layers of magnetism; and other equipment to measure the ability of minerals to retain a residual magnetic field.

Outside the room, New Haven’s magnetic field is approximately 55,800 nanoTeslas; inside the chamber, it’s 100 nanoTeslas. A nanoTesla is a unit of magnetic flux density.

“Basically, we’re entering the instrument itself,” McIntosh said, pushing through a curtain covered with an image of Aion-Kronos, the Greek god of infinite time.

There Fernandez was working on his samples. Many of them were particles of scorched earth that she recovered last summer from archaeological sites in northern Peru. It focuses on the Moche civilization, which flourished in Peru from AD 100 to AD 800.

“It helps improve the regional dating curve for South America which is used to estimate the age of culturally significant pottery samples and other heated archaeological objects,” said Joshua Feinberg, associate director of the Institute. for Rock Magnetism from the University of Minnesota.

The Yale facility has started to attract the interest of a number of scientists across the country, including Feinberg. “My own research at the University of Minnesota uses mineral magnetism to answer questions in both archeology and geoscience,” Feinberg said. “Given the cutting-edge research conducted by Rod McIntosh and [geology and geophysics professor] David Evans, I look forward to spending much more time working and learning with the students and researchers at Yale.

Back in the lab, Fernandez tested each of his samples several times. The samples are coated with plaster to maintain their consistency during the experiments.

“This is where I spend most of my afternoons and evenings,” she said. His thoughts then returned to Le Moche. “It was such a complex society, as complex as the Inca societies. Providing archaeologists with another lens through which these sites are updated is so gratifying to me. “

His research will also have a wider impact. There are few historical markers for Earth’s electromagnetic fields in the southern hemisphere – most readings are taken in the northern hemisphere by geologists – so the measurements established by Fernandez will likely be used by researchers for many years to come. many years.

“Yale is leading the way in using these techniques,” McIntosh said. “When I tell geologists some of the things we do, they are blown away. “


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