AMMONIA IN THE EARLY SOLAR SYSTEM: AN ACCOUNT FROM CARBONACEOUS METEORITES

This study presents a survey of abundance distribution and isotopic composition of the ammonia found incorporated in the kerogen-like insoluble material of selected carbonaceous chondrite meteorites; the ammonia was released upon hydrothermal treatment at 300 degrees C and 100 MPa. With the exception of Allende, a metamorphosed and highly altered stone, all the insoluble organic materials (IOM) of the meteorites analyzed released significant amounts of ammonia, which varied from over 4 mu g mg(-1) for the Orgueil IOM to 0.5 mu g mg(-1) for that of Tagish Lake; the IOM of the pristine Antarctica find GRA95229 remains the most rich in freeable ammonia with 10 mu g mg(-1). While the amounts of IOM bound ammonia do not appear to vary between meteorites with a recognizable trend, a possible consequence of long terrestrial exposure of some of the stones, we found that the delta N-15 composition of the ammonia-carrying materials is clearly distinctive of meteorite types and may reflect a preservation of the original N-15 distribution of pre- and proto-solar materials.