Originally published 18 November 2003
Remember the iceman? A dozen years ago, a couple of hikers found a mummified body in a melting glacier high in the Alps, on the border between Austria and Italy.
The iceman — dubbed Ötzi after the Ötz valley near where he was found — was about 46 years old when he died, apparently the victim of violence, an arrowhead in his shoulder. His body was quickly covered with snow. When found, he had been entombed in ice for 5,200 years.
Ötzi’s mummified cadaver offers a unique snapshot of Late Neolithic-Copper Age life. Scientists have analyzed the contents of Ötzi’s stomach, sequenced his DNA, studied his grass cloak, goatskin coat, leggings, belt, shoes, cap, even his underwear.
Now some incredibly clever detective work by an international team of scientists, led by Wolfgang Müller of Australian National University in Canberra, has tracked Ötzi’s lifelong travels, from the place where he cut his first permanent teeth to the high alpine pass where he died.
The work is reported in the October 31 [2003] issue of the journal Science.
Astonishingly, Ötzi’s peregrinations are recorded in the atoms of his body, and the clues are sorted out with an instrument called a mass spectrometer.
A “mass-spec” specialist can tell what atomic elements are in any sample of matter, and how much of each element. Isotopes of the same element — atoms that differ only by the number of neutrons in the nucleus — can also be distinguished and counted.
Bits of Ötzi’s tooth and thigh were subjected to mass-spec analysis and made to tell their tale.
The material in tooth enamel is fixed forever at the time the tooth forms, typically at age 3 to 5, so the isotopic composition of dental enamel — the relative amounts of each isotope of constituent atoms — should be identical to that of the food and water Ötzi consumed when he was a young child.
Ötzi’s food, in turn, would bear the isotopic signatures of the soil in which it was grown. By comparing the composition of Ötzi’s tooth enamel to soils in the region of the Austrian-Italian border, the researchers deduced where Ötzi spent his youth: the Elsack Valley, about 40 miles southeast of where his body was found.
Oxygen atoms in Ötzi’s teeth provided a confirming clue.
Oxygen in tooth enamel is primarily derived from ingested water. There are two stable isotopes of oxygen, oxygen-16 (8 protons and 8 neutrons) and oxygen-18 (8 protons and 10 neutrons). Water molecules (H2O) containing the heavier isotope of oxygen tend to precipitate more quickly as rain, and therefore the ratio of oxygen isotopes in ground water varies from place to place, depending on weather patterns and distance from the sea.
Matching the isotopic composition of oxygen in Ötzi’s teeth to present-day water sources helped the researchers pin down where Ötzi spent his youth.
Unlike tooth enamel, the material of bones is replaced in the body every 10 or 20 years. The same kind of mass-spec analysis with bits of Ötzi’s thighbone told the researchers where he spent the last 10 or 20 years of his life, higher in the mountains and miles away from the Elsack Valley.
Finally, the age of tiny bits of mica from food in Ötzi’s intestines, presumably fragments of the stone used to grind the grain from which the food was made, was determined using radioactive isotopes of argon in the mica. The age matches that of rock just south of the place where Ötzi’s body was found.
By counting atoms with a mass spectrometer, Ötzi’s life story unfolds, from his place of birth in the Elsack Valley, to his adulthood at a higher alpine elevation, finally to the snowy ridge where he met his untimely death.
If nothing else, this clever piece of work proves that Late Neolithic-Copper Age people were not necessarily homebodies. Ötzi, certainly, got around, although we may never know what took him so high in the mountains.
But never mind. This is one of those science stories that is interesting not so much for what is done as for the fact that it can be done at all.
