The Isotopic Composition of Iron: A Chemical Fingerprint forBiologic Activity

9713968约翰逊·比尔德该奖项支持一个项目，该项目旨在开发一种利用铁(Fe)的同位素组成对陨石中的生物活动进行指纹识别的化学方法。它得到了极地计划办公室、化学司和MPS多学科活动办公室的支持。开发生物化学指纹将有助于：1)评估最近的解释，即陨石ALH84001包含火星上古代生物活动的证据，部分以超细颗粒磁铁矿和硫化铁矿物的形式存在，据推测这些矿物是由铁还原细菌形成的；2)筛查外星物质的生物活动(陨石或未来任务返回其他行星的样本)；3)确定地球上最早的生命的时间限制。生物产生的含铁矿物无处不在，许多铁生物矿物是由细菌产生的，这些细菌将铁还原为亚铁，从而形成铁氧化物、硫化物或碳酸盐。铁还原的代谢途径与细菌将硫酸盐还原为硫化物的代谢途径相同。硫酸盐的细菌还原可以产生硫-34与硫-32比率的大的分馏。通过与硫酸盐还原细菌的类比，根据铁和S同位素的相对质量分布，铁还原细菌有望产生与硫酸盐还原细菌观察到的铁同位素分馏大致相当的铁同位素分馏。这种分馏程度是由Dixon等人对铁同位素的初步研究提出的，他们解释了他们在陆地样品中测量的铁同位素比率变化，以反映生物诱导的铁同位素分馏。这项研究的范围将是通过分析从各种物理环境中产生的无机含铁矿物来确定无机铁的同位素组成的基线。将通过分析在受控实验室环境中从分离的细菌菌株中生长的铁生物矿物质来评估生物过程产生的铁同位素分馏。有了这些限制，就有可能利用铁的同位素组成来评估火星陨石ALH84001中推断的铁生物矿物是无机产生的还是生物活动产生的。

9713968 Beard, Johnson Abstract This award supports a project to develop a chemical method for fingerprinting biological activity in meteorites using the isotopic composition of iron (Fe). It is supported by the Office of Polar Programs, the Chemistry Division, and the MPS Office of Multidisciplinary Activities. Development of a biological chemical fingerprint will be useful in: 1) evaluating the recent interpretations that meteorite ALH84001 contains evidence of ancient biological activity on Mars, partly in the form of ultra-fine-grained magnetite and sulfide iron minerals that are inferred to have been formed by iron-reducing bacteria; 2) screening extraterrestrial material for biological activity (meteorites or samples returned from future missions to other planets); and 3) establishing the time limits for the earliest life on Earth. Biologically produced iron-bearing minerals are ubiquitous, and many iron biominerals are produced by bacteria that reduce ferric iron to ferrous iron, resulting in formation of iron-oxides, - sulfides, or -carbonates. The metabolic pathway for iron reduction is the same as that used by bacteria which reduce sulfate to sulfide. Bacteria reduction of sulfate can produce large fractionations in sulfur-34 to sulfur-32 ratios. By analogy to sulfate-reducing bacteria, iron reducing bacteria are expected to be capable of producing Fe isotope fractionations that are on the order of those observed for sulfate reducing bacteria, based on the relative mass spread of Fe and S isotopes. This magnitude of fractionation is suggested by preliminary studies of Fe isotopes by Dixon et al., who interpret the Fe isotope ratio variations they measured in terrestrial samples to reflect biologically-induced Fe isotope fractionation. The scope of this research will be to establish a baseline for the isotopic composition of inorganic iron by analysis of inorganically produced Fe-bearing minerals from a variety of physical settings . Evaluating the Fe isotope fractionation produced by biological processes will be conducted by analyzing iron biominerals that were grown from isolated bacteria strains in a controlled laboratory environment. With these limits established, it will be possible to use the isotopic composition of Fe to evaluate if inferred iron biominerals in Martian meteorite ALH84001 were produced inorganically or by biological activity.