Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: TUESDAY, November 28, 1995 TAG: 9511290043
SECTION: EXTRA PAGE: 6 EDITION: METRO
SOURCE: MATT CRENSON DALLAS MORNING NEWS
DATELINE: DALLAS LENGTH: Medium
Writing in October's Geology, researchers from the University of Michigan in Ann Arbor and the University of Copenhagen in Denmark traced the climate history of Greenland using the teeth of Norse settlers and native Inuit inhabitants. The teeth suggest that warmer temperatures during the Middle Ages allowed the Norse to survive in Greenland, but that a cooler period, known as the Little Ice Age, eventually wiped them out.
There already is archaeological evidence suggesting such a scenario, Danish anthropologist Niels Lynnerup and Michigan geologists Henry Fricke and James O'Neil wrote. But the fact that their results agree with what's known gives the researchers more confidence in the new method's potential.
``There's just a lot of neat stuff out there that's waiting to be done,'' Fricke said.
The method relies on different forms of oxygen, known as isotopes, in the enamel of the teeth. Tooth enamel, which is produced during childhood and adolescence, is made with water and other substances from the environment.
Colder rainwater contains less of one isotope, oxygen-18, than does warmer precipitation. So the proportion of oxygen-18 in a person's tooth enamel is tied to the temperature of the rainwater that individual drinks.
The geologists confirmed that tooth enamel indicates temperature differences by comparing the teeth of Inuit living in Disko Bay, Greenland about 500 years ago, to inhabitants of Denmark who lived at about the same time. Today the average annual temperature difference between the two places is more than 30 degrees Fahrenheit, and the tooth enamel indicates that it was about the same five centuries ago.
The geologists estimate that they can use tooth enamel to determine average annual temperature within about 2 degrees Fahrenheit. That's enough detail to track ancient climate changes that happened over periods of 100 years or less.
``These records can then be used to provide important constraints on the response of human groups to climate variations,'' the geologists wrote.
Some archaeologists theorize that in Greenland, unusually warm climates allowed Norse settlers to colonize coastal regions in about A.D. 1000. They thrived for several centuries, but their means of subsistence - sheep and cattle grazing - wasn't ecologically sustainable over the long term in such a harsh climate.
The Greenland Norse were already in decline by 1350, when they abandoned one of their two major settlements. But the sudden inception of cooler temperatures at about that time probably finished the Norse off over the next century or so, archaeologists theorize.
Teeth collected from Norse churchyards in southern and western Greenland support that interpretation. Especially in southern Greenland, human teeth show a decline in the abundance of oxygen-18 - and thus a fall in average temperature - from about A.D. 1000 to 1700, when Inuit were the region's only remaining inhabitants.
The method isn't perfect. For example, the geologists think their results may be skewed by the fact that some of the Norse settlers buried in Greenland actually spent childhood and adolescence in Norway or Iceland. If that's the case - and it almost certainly is - then those people would have tooth enamel isotopes reflecting the region where they grew up, not where they were buried.
But even with some complications, the method seems to have worked when applied to medieval Greenland.
``It's the first time it's really been done ... so different things come up,'' Fricke said. ``We're just sort of playing it by ear.''
by CNB