By Sid Perkins
Two layers of ice recently found in an ice core drilled from East Antarctica are heavily contaminated with meteoritic dust—the first such extraterrestrial debris ever recovered from deep Antarctic ice.
At first, geologist Biancamaria Narcisi of the Casaccia Research Center in Rome and her colleagues thought the dark particles spread throughout each layer of ice were volcanic ash. As many as 18 layers of such ash have been found in the 3.26-kilometer-long ice core that she and other scientists have analyzed.
The newly described particles don’t look like volcanic ash, however. Instead, their crystal structure and chemical composition match those of particles found in many meteorites. Many of the bits are 10 micrometers across or larger, much bigger than the 2-µm-or-smaller dust particles that waft to the region from distant deserts. Moreover, some of the particles are spherical and glasslike, signs that they melted as they tore through Earth’s atmosphere.
Narcisi and her colleagues estimate that the debris-rich layers, found at depths of 2,788 and 2,833 meters, are about 434,000 and 481,000 years old, respectively. Finding comparable layers in other Antarctic ice cores could help calibrate the dating of those cores and thus pin down the ages of events chronicled in them, the researchers suggest in the Aug. 18 Geophysical Research Letters.
