40,000 tons of extraterrestrial matter are believed to hit the Earth every year. This from the current issue of Science, where researchers from New York (Columbia University) and Bremerhaven (Alfred-Wegener-Institut) present a study of helium isotopes found in Antarctic ice cores. Over the last 30,000 years, the scientists believe, the amount of 3He, a rare isotope found in cosmic dust, exceeds that found in terrestrial dust in ice by a factor of 5000. We have, the investigation indicates, been subject to a constant rain of cosmic dust particles over this period.

Which is interesting in its own right, but becomes more pointed when you look at the measurements of the helium isotope 4He, which is much more common on Earth. Indications point to a change of origins in terrestrial dust between the last Ice Age and the current interglacial warm period.

Says Gisela Winckler (Lamont-Doherty Earth Observatory, Columbia University):

“The terrestrial dust coming down on Antarctica during the Ice Age obviously is not the same as that during warm periods. This may be due to the mineral dust originating from different regional sources or to changes in weathering, the process responsible for production of dust.”

And from the paper itself:

We suggest that different dust sources, exposed continental shelves, or freshly generated glaciogenic material may have influenced the glacial dust deposition on the Antarctic ice sheet.

The Antarctic evidence suggests that changes in terrestrial dust between the last Ice Age and today are significant in terms of climate change, whereas extraterrestrial matter inflows seem constant during the same period. As the scientists put it in their abstract: “This finding excludes 3He as a pacemaker of late Pleistocene glacial cycles. Rather, it supports 3He as a constant flux parameter in paleoclimatic studies.”

The paper is Winckler and Fischer, “30,000 Years of Cosmic Dust in Antarctic Ice,” Science 313, p. 491 (July 28, 2006), with abstract available here. Thanks to Anthony Kendall, author of the fine Anthonares site, for his help in preparing this story.