Behavior of polycyclic aromatic hydrocarbons at impact shock: Its implication for survival of organic materials delivered to the early Earth
Behavior of polycyclic aromatic hydrocarbons at impact shock: Its implication for survival of organic materials delivered to the early Earth
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DOI：
10.1016/j.gca.2004.06.020
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发表时间：
2005-01-01
影响因子：
5
通讯作者：
Toyama, S
中科院分区：
文献类型：
--
作者：
Mimura, K;Toyama, S
通过对多环芳烃（PAHs）与含水和无水矿物基质的碰撞分析，研究了多环芳烃的抗冲击行为。冲击实验的结果表明，从含水矿物释放的挥发物不影响多环芳烃的抗冲击行为。冲击样品含有未反应的起始多环芳烃，不溶于二氯甲烷的烟灰样物质，和二次形成的多环芳烃分子量范围从128到404。约95%的起始多环芳烃在30 GPa左右的压力下分解，主要产物为煤烟状物质。冲击波产物的形成机理用静态高压-温度条件下的反应过程来解释（例如，碳化，自由基加成反应，环交联和甲基化）。我们应用这些结果来估计在早期地球的吸积阶段，碳质小行星提供的有机物质对它们的撞击压力的存活程度。如果我们使用一个简化的无大气的均匀吸积模型来表示这个阶段，那么对于碳质小行星的撞击，导致30 GPa（多环芳烃几乎分解的压力）的地球半径计算为2270 km（4.0 km s（-1）的撞击速度）。在早期地球上，撞击物撞击的不是陆地而是海洋，多环芳烃分解的撞击速度估计为6.0 km/s（-1）。由于撞击物在稠密大气中的空爆和气爆，这些撞击速度在早期的地球上应该是普遍存在的。早期的地球应该是一个有利的环境，以获得和维持大量的生命前有机物质导致生命。版权所有（C）2005 Elsevier Ltd.
Polycyclic aromatic hydrocarbons (PAHs) with a hydrous or an unhydrous mineral matrix were impacted and analyzed, to study the behavior of PAHs against shock. Results of the shock experiments suggested that volatiles discharged from the hydrous mineral did not influence the behavior of PAHs against shock. The shocked samples contained unreacted starting PAHs, soot-like materials insoluble in dichloromethane, and secondarily formed PAHs with molecular weights ranging from 128 to 404. Approximately 95% of starting PAHs decomposed at similar to30 GPa and the dominant product was the soot-like materials. Formation mechanisms of the shock products were explained by reaction processes under static high pressure-temperature conditions (e.g., carbonization, radical addition reaction, ring cross linking, and methylation).We applied these results to estimate the survival degree of organic matter delivered by carbonaceous asteroids against their impact pressures at the accretion stage of early Earth. If we use a simplified homogeneous accretion model without atmosphere to represent the stage, the radius of Earth causing 30 GPa, the pressure at which PAHs almost decompose, was calculated as 2270 km (4.0 km s(-1) of impact velocity) for the impact of carbonaceous asteroids. In the case of impactors striking not land but oceans on the early Earth, the impact velocity for the decomposition of PAHs was estimated to be 6.0 km s(-1). These impact velocities should have been commonly realized on the early Earth, due to the airburst and the aerobreak of impactors in the dense atmosphere. The early Earth should have been a favorable environment for obtaining and maintaining a large quantity of prebiotic organic materials leading to life. Copyright (C) 2005 Elsevier Ltd.