Thomas-Keprta K L, Clemett S J, Bazylinski D A, Kirschvink J L, McKay D S, Wentworth S J, Vali H, Gibson E K, McKay M F, Romanek C S
Lockheed Martin, 2400 NASA Road 1, Mail Code C23, Houston, TX 77058, USA.
Proc Natl Acad Sci U S A. 2001 Feb 27;98(5):2164-9. doi: 10.1073/pnas.051500898.
McKay et al. [(1996) Science 273, 924-930] suggested that carbonate globules in the meteorite ALH84001 contained the fossil remains of Martian microbes. We have characterized a subpopulation of magnetite (Fe(3)O(4)) crystals present in abundance within the Fe-rich rims of these carbonate globules. We find these Martian magnetites to be both chemically and physically identical to terrestrial, biogenically precipitated, intracellular magnetites produced by magnetotactic bacteria strain MV-1. Specifically, both magnetite populations are single-domain and chemically pure, and exhibit a unique crystal habit we describe as truncated hexa-octahedral. There are no known reports of inorganic processes to explain the observation of truncated hexa-octahedral magnetites in a terrestrial sample. In bacteria strain MV-1 their presence is therefore likely a product of Natural Selection. Unless there is an unknown and unexplained inorganic process on Mars that is conspicuously absent on the Earth and forms truncated hexa-octahedral magnetites, we suggest that these magnetite crystals in the Martian meteorite ALH84001 were likely produced by a biogenic process. As such, these crystals are interpreted as Martian magnetofossils and constitute evidence of the oldest life yet found.
麦凯等人[（1996年）《科学》273卷，924 - 930页]提出，陨石ALH84001中的碳酸盐小球含有火星微生物的化石遗迹。我们已对这些碳酸盐小球富铁边缘大量存在的磁铁矿（Fe(3)O(4)）晶体的一个亚群进行了表征。我们发现这些火星磁铁矿在化学和物理性质上与趋磁细菌菌株MV - 1产生的地球上生物成因沉淀的细胞内磁铁矿相同。具体而言，这两种磁铁矿群体都是单畴且化学纯的，并呈现出一种我们称为截顶六八面体的独特晶体习性。在地球上的样本中，尚无已知的无机过程能解释截顶六八面体磁铁矿的观测结果。因此，在细菌菌株MV - 1中，它们的存在可能是自然选择的产物。除非火星上存在一种地球上明显不存在且能形成截顶六八面体磁铁矿的未知且无法解释的无机过程，否则我们认为火星陨石ALH84001中的这些磁铁矿晶体很可能是由生物成因过程产生的。据此，这些晶体被解释为火星磁化石，构成了迄今发现的最古老生命的证据。
