Number 301 (Story #1), December 31, 1996 by Phillip F. Schewe and Ben Stein OXYGEN DATING THE MILKY WAY . A new technique uses stardust to formulate an age for our galaxy. By looking at the isotopic composition of meteorites, scientists can tell whether certain grains came from outside the solar system. Such specks of matter would also necessarily predate the solar system and would have originated in other stars, either as part of the stellar wind gusting away from red giant stars or as the debris of ancient supernovas (Science, 15 November). Larry Nittler, now of the Carnegie Institution of Washington (202- 686-4370, x4421), has sorted 87,000 oxide grains according to two composition ratios: O-16/O-17 and O-16/O-18. From this huge sample he has isolated 87 grains that seem to be "presolar" in nature. Employing these bits of stardust to represent extrasolar material, and using theories about how the heavier elements are cooked in successive cycles of supernovas, Nittler can estimate an age for the Milky Way galaxy---14.4 (with a statistical uncertainty of 1.3) billion years. (L.R. Nittler and R. Cowsik, upcoming article in Physical Review Letters.)