Anders E
Department of Chemistry, University of Chicago, Illinois 60637-1433, USA.
Nature. 1989 Nov 16;342(6247):255-7. doi: 10.1038/342255a0.
Several authors have suggested that comets or carbonaceous asteroids contributed large amounts of organic matter to the primitive Earth, and thus possibly played a vital role in the origin of life. But organic matter cannot survive the extremely high temperatures (>10(4) K) reached on impact, which atomize the projectile and break all chemical bonds. Only fragments small enough to be gently decelerated by the atmosphere--principally meteors of 10(-12)-10(-6) g--can deliver their organic matter intact. The amount of such 'soft-landed' organic carbon can be estimated from data for the infall rate of meteoritic matter. At present rates, only approximately 0.006 g cm-2 intact organic carbon would accumulate in 10(8) yr, but at the higher rates of approximately 4 x 10(9) yr ago, about 20 g cm-2 may have accumulated in the few hundred million years between the last cataclysmic impact and the beginning of life. It may have included some biologically important compounds that did not form by abiotic synthesis on Earth.
几位作者提出，彗星或碳质小行星为原始地球贡献了大量有机物质，因此可能在生命起源中发挥了至关重要的作用。但是，有机物质无法在撞击时达到的极高温度（>10⁴ K）下存活，这种高温会使抛射体原子化并打破所有化学键。只有小到足以被大气缓慢减速的碎片——主要是质量为10⁻¹² - 10⁻⁶ 克的流星体——才能完整地输送其有机物质。这种“软着陆”有机碳的数量可以根据陨石物质的降落速率数据来估算。按照目前的速率，在10⁸ 年里只有大约0.006克每平方厘米的完整有机碳会积累下来，但在大约4×10⁹ 年前的较高速率下，在最后一次灾难性撞击和生命开始之间的几亿年里，可能积累了约20克每平方厘米。它可能包含一些在地球上并非通过非生物合成形成的对生物学很重要的化合物。
