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 analys es of micrometeorites and meteorites indicate that micrometeorites are most ly related to the relatively rare group (2% of the meteorite falls) of the primitive hydrous-carbonaceous meteorites, and not to the most abundant cla sses of the ordinary chondrites and differentiated meteorites. But there ar e differences between these two classes of extraterrestrial objects, such a s a high pyroxene to olivine ratio, a strong depletion in chondrules, a muc h smaller size of the most refractory components, and a much higher AIB (al pha -isobutyric amino acid) to isovaline ratio in micrometeorites as compar ed to meteorites. They indicate that micrometeorites represent a new popula tion of solar system objects, not represented as yet in the meteorite colle ctions. The major objective of this work is to predict various effects of t he accretion of early micrometeorites on the Earth during the period of hea vy 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 select ion of measurements (average contents of neon, carbon, nitrogen and water i n micrometeorites, and isotopic composition of their Ne and H), shows that during the peak of this cataclysmic epoch (sterilization period) which occu rred just after the formation of the young Earth (4.45 Ga ago), the accreti on of early micrometeorites did play a major role in the formation of the t errestrial atmosphere and oceans. Later on, during the early life period (a round 4 Ga ago), when liquid water and organics could condense and/or survi ve, 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 "earl y-micrometeorite-accretion" scenario (EMMAC), which is finally extended wit h some confidence to Mars, where the survival of micrometeorites upon atmos pheric entry looks even more favorable than on the Earth. (C) 2000 Elsevier Science Ltd. All rights reserved.