Accretion of neon, organics, CO2, nitrogen and water from large interplanetary dust particles on the early Earth

Large interplanetary dust particles (micrometeorites) with sizes of 100-200 mum, recovered from the Greenland and Antarctica ice sheets, represent by far the dominant source of primitive extraterrestrial material accreted by the Earth today. Comparisons of mineralogical, chemical and isotopic analyses of micrometeorites and meteorites indicate that micrometeorites are mostly related to the relatively rare group (2% of the meteorite falls) of the primitive hydrous-carbonaceous meteorites, and not to the most abundant classes of the ordinary chondrites and differentiated meteorites. But there are differences between these two classes of extraterrestrial objects, such as a high pyroxene to olivine ratio, a strong depletion in chondrules, a much smaller size of the most refractory components, and a much higher AIB (alpha -isobutyric amino acid) to isovaline ratio in micrometeorites as compared to meteorites. They indicate that micrometeorites represent a new population of solar system objects, not represented as yet in the meteorite collections. The major objective of this work is to predict various effects of the accretion of early micrometeorites on the Earth during the period of heavy bombardment suffered by the Earth-Moon system greater than or equal to 3.9 Ga ago. The application of a simple arithmetics of accretion to a selection of measurements (average contents of neon, carbon, nitrogen and water in micrometeorites, and isotopic composition of their Ne and H), shows that during the peak of this cataclysmic epoch (sterilization period) which occurred just after the formation of the young Earth (4.45 Ga ago), the accretion of early micrometeorites did play a major role in the formation of the terrestrial atmosphere and oceans. Later on, during the early life period (around 4 Ga ago), when liquid water and organics could condense and/or survive, micrometeorites were possibly functioning as tiny chemical reactors to synthesize the prebiotic molecules required for the origin of life. Efforts were made to start reducing the number of major speculations in this early-micrometeorite-accretion scenario (EMMAC), which is finally extended with some confidence to Mars, where the survival of micrometeorites upon atmospheric entry looks even more favorable than on the Earth. (C) 2000 Elsevier Science Ltd. All rights reserved.