The volatile fingerprints of life - a new method to indicate the biological or non-biological sources of gas

碳氢化合物气体在宇宙和地圈中很常见。碳氢化合物气体的生物或非生物来源往往是辩论的主题，争论的强度取决于碳氢化合物气体的位置和可用来解决任何不确定性的信息量。不幸的是，碳氢化合物可能是信息相对贫乏的化合物。它们的小尺寸使得它们的分子结构不能诊断来源。具有不同碳原子数的气体模式确实提供了一些信息，但这些化合物中信息最丰富的部分是原子本身。组成碳氢化合物骨架的碳原子包含两个稳定的同位素，碳-12和碳-13。较轻的碳同位素比较重的碳同位素活性更强，更容易参与反应。在反应产物中优先掺入较轻的碳同位素导致同位素分馏，可以揭示合成机理。非生物碳氢化合物通常显示碳-12随着碳数的增加而增加，这与由较简单的前体动力学控制合成较高分子量同系物的情况一致。相比之下，高分子量生物衍生碳氢化合物的热裂解产生相反的趋势，观察到碳-12随着碳数的减少而减少。这个项目将探索与非生物过程相关的碳氢化合物气体的组成和模式，并将这些与典型的与生命有关的模式进行比较。该产品应改进用于区分与生物或非生物来源相关的气体成分特征的标准。在伦敦帝国理工学院，我们开发了一种定制的解吸池，可以将具有代表性的样品的粉末或插头装入其中。已知体积和组成的气体可以被引入并吸附到内容物上，然后通过减压释放。利用在线气相色谱-火焰离子化检测器(GC-FID)和在线气相色谱-同位素比质谱仪(GC-C-IRMS)系统对从解吸室回收的气体进行测量，分别研究分子量和稳定碳同位素分馏。该项目的结果将对早期太阳系挥发和大气的演化、对火星上任何生命的气体的识别以及地球上石油矿床的非生物形成理论具有重要意义。

Hydrocarbon gases are common in the Cosmos and the geosphere. The biological or non-biological source of hydrocarbon gases is often the subject of debate, the intensity of which depends on the location of the hydrocarbon gas and the amount of information available to settle any uncertainty. Unfortunately, hydrocarbon gases can be relatively information poor compounds. Their small size makes their molecular architecture undiagnostic of source. Patterns of gases with different numbers of carbon atoms do provide some information but the most information rich part of these compounds is within the atoms themselves.The carbon atoms that make up the skeleton of hydrocarbons contain two stable isotopes, carbon-12 and carbon-13. The lighter carbon isotope is more reactive than its heavier counterpart and takes part in reactions more readily. The preferential incorporation of the lighter carbon isotope in reaction product leads to isotope fractionation and can reveal synthetic mechanisms. Non-biological hydrocarbons generally reveal an increase in carbon-12 with carbon number in accord with the kinetically controlled synthesis of higher molecular weight homologues from simpler precursors. By contrast the thermal cracking of high molecular weight biologically-derived hydrocarbons produces the opposite trend where a decrease in carbon-12 with carbon number is observed.This project will explore the compositions and patterns in hydrocarbon gases associated with abiological processes such as adsorption and desorption and compare these to patterns typically associated with life. The product should be improved criteria for distinguishing gas compositional signatures associated with biological or abiological origins. At Imperial College London we have developed a custom-built desorption cell into which powders or plugs of representative samples can be loaded. Known volumes and compositions of gas can be introduced and adsorbed onto the contents and then released by depressurization. Measurement of the gas recovered from the desorption cell is performed using coupled online gas chromatography - flame ionising detector (GC-FID) and online gas chromatography - isotope ratio mass spectrometry (GC-C-IRMS) systems to study molecular weight and stable carbon isotopic fractionation respectively.The results of the project will have implications for the evolution of volatiles and atmospheres in the early solar system, the recognition of gases from any life on Mars and theories of abiotic formation of petroleum deposits on Earth.