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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Potential of EPR imaging to detect traces of primitive life in sedimentary rocks
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Potential of EPR imaging to detect traces of primitive life in sedimentary rocks

机译：EPR成像技术可探测沉积岩中原始生命的痕迹

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摘要

In the prospect of the search for traces of primitive life on Earth and Mars, we investigated the possibility to detect and visualize the spatial distribution of minute amounts of organic matter in ancient rocks, in a non-destructive way, by Electron Paramagnetic Resonance Imaging (EPRI). We studied a series of non- or moderately metamorphosed siliceous rocks (cherts) of different ages ranging from 45 Ma to 3490 Ma and embedding fossile organic matter. In the case of the oldest cherts containing only mature insoluble organic matter (IOM), with IOM center dot radicals characterized by a single Electron Paramagnetic Resonance (EPR) line, we could obtain three-dimensional images with sub-millimetric resolution of the organic matter distribution inside samples containing as low as 10(14)-10(15) radicals per gram. In the case of younger cherts, containing less mature organic matter, and thus several types of organic radicals, we showed that selective imaging of each type of radical was possible provided that the EPR spectra did not overlap. Selective imaging of either the organic radicals or of the oxygen vacancy (E' centres) of the mineral matrix, which are ubiquitous in siliceous rocks, was possible, selecting either one or the other paramagnetic species with high power in-phase, 1st harmonic detection or with 90 degrees-out-of-phase, 2nd harmonic detection of the EPR. The influence of ferromagnetic inclusions in the mineral matrix on the EPRI of the organic matter was also addressed. Image artifacts due to the ferromagnetic resonance signal of these inclusions could be easily removed by background substraction from the EPR spectra before image reconstruction. We thus showed that selective imaging by EPR of minute amounts of fossile organic matter in ancient rocks could be possible despite the magnetic complexity of such materials.
机译：为了寻找地球和火星上原始生命的踪迹，我们研究了通过电子顺磁共振成像（无损方式）以无损方式检测和可视化古代岩石中微量有机物的空间分布的可能性（ EPRI）。我们研究了一系列年龄从45 Ma到3490 Ma的非变质或中等变质的硅质岩（cher石），并嵌入了化石有机质。对于仅包含成熟的不溶有机物（IOM）的最古老的ts石，其IOM中心点自由基具有单电子顺磁共振（EPR）线的特征，我们可以获得具有亚毫微米分辨率的有机物的三维图像样品内部分布低至每克10（14）-10（15）个自由基。在较年轻的石中，含有较少的成熟有机物，因此有几种类型的有机基团，我们证明，只要EPR光谱不重叠，就可以对每种类型的基团进行选择性成像。可以对硅质岩中普遍存在的矿物基体中的有机基团或氧空位（E'中心）进行选择性成像，选择一种或另一种具有高功率同相，一次谐波检测的顺磁性物质或具有90度异相的EPR二次谐波检测。还解决了矿物基质中铁磁夹杂物对有机物EPRI的影响。在图像重建之前，可以通过从EPR光谱中扣除背景来轻松消除由于这些夹杂物的铁磁共振信号而导致的图像伪影。因此，我们表明，尽管磁性材料很复杂，但通过EPR对古代岩石中微量的化石有机物进行选择性成像仍是可能的。

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