by Aimee Gillespie Monday, July 1, 2013
In ancient Egypt, iron was a rare and symbolic metal, but scientists and historians have long wondered about the prehistoric civilization’s knowledge of metallurgy. Now, one part of that mystery has been solved: The oldest-known iron artifacts were made from meteorites. The evidence comes in the form of iron beads from approximately 3300 B.C., more than 2,000 years before the Iron Age in Egypt, and before there is record of trade in iron goods with other civilizations.
The iron beads come from a tomb in the prehistoric Gerzeh cemetery, on the bank of the Nile about 70 kilometers south of Cairo. The tomb belonged to a “fair-sized boy,” according to notes the excavator took when the tomb was discovered more than a century ago. Seven iron beads were placed around the boy’s neck and waist. The beads appear to be jewelry, and were found with other exotic materials like obsidian and ivory.
In a study in the journal, Meteoritics & Planetary Science, Diane Johnson, a geochemist at the Open University in England, and her colleagues analyzed the chemical composition of one of the iron beads from the tomb to settle a century-long debate about the origin of the metal: terrestrial or celestial.
The ancient bead looks very different today than it did millennia ago: It is extensively rusted, and the surface of the bead is caked with sand from the tomb. But in some areas, the rust has fallen away, allowing researchers to peer inside and analyze the original metal using a scanning electron microscope. They found that the iron consists of an alloy with approximately 30 percent nickel — a signature of iron meteorites. When metallic iron coalesces to form the core of an asteroid or planet, it takes most of the nickel with it, as is the case here on Earth. Most iron ore mined on Earth’s surface contains very little nickel, but nickel-rich iron can be found on the surface in the remnants of broken-up cores of ancient asteroids, which fall to Earth as meteorites.
The researchers also observed another characteristic of meteorites: the so-called Widmanstätten pattern. As they scanned the bead, they saw telltale bands of the iron-nickel minerals taenite and kamacite. The Widmanstätten pattern only occurs if the metal cools and crystallizes at an incredibly slow rate, as it does in the cores of asteroids.
To learn more about the iron-working skills of ancient Egyptians the researchers also performed a CT scan of the bead, which allowed them to construct a 3-D image of its structure. The scan revealed points of bending and a joining edge in the metal,, clues that revealed that the bead had been made by pounding a piece of iron flat and bending it into a tube.
This study “feeds into the larger and very important picture of the development of iron-working and iron smelting or cold-working in Egypt,” which has been controversial, says Julie Anderson, a curator in the Department of Ancient Egypt and Sudan at the British Museum in London who was not involved in this research. The controversy stems from the fact that there is no written record of iron-working during this period, and a lack of direct evidence from which scientists and historians can learn. Analyses of more iron artifacts are needed to expand on this work and shed new light on the issue, Anderson says.
It is not clear if the celestial origin of the meteorite was recognized by the Egyptians who made the bead in 3300 B.C., “especially as they date from a time that predates writing,” Johnson says. But about 2,000 years later, Egyptians began using the term “biA-n-pt” for iron, which means “iron from the sky.” It’s possible, her team wrote, that this term was born out of an event like a large meteor impact or a meteor shower.
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