1 TGE Réseau National de RPE interdisciplinaire (RENARD, FR-CNRS 3443).
Astrobiology. 2013 Oct;13(10):932-47. doi: 10.1089/ast.2013.0971. Epub 2013 Oct 4.
The search for organic biosignatures is motivated by the hope of understanding the conditions of emergence of life on Earth and the perspective of finding traces of extinct life in martian sediments. Paramagnetic radicals, which exist naturally in amorphous carbonaceous matter fossilized in Precambrian cherts, were used as local structural probes and studied by electron paramagnetic resonance (EPR) spectroscopy. The nuclear magnetic resonance transitions of elements inside and around these radicals were detected by monitoring the nuclear modulations of electron spin echo in pulsed EPR. We found that the carbonaceous matter of fossilized microorganisms with age up to 3.5 billion years gives specific nuclear magnetic signatures of hydrogen (¹H), carbon (¹³C), and phosphorus (³¹P) nuclei. We observed that these potential biosignatures of extinct life are found neither in the carbonaceous matter of carbonaceous meteorites (4.56 billion years), the most ancient objects of the Solar System, nor in any carbonaceous matter resulting from carbonization of organic and bioorganic precursors. These results indicate that these nuclear signatures are sensitive to thermal episodes and can be used for Archean cherts with metamorphism not higher than the greenschist facies.
寻找有机生物特征的动机是为了了解地球上生命出现的条件，以及在火星沉积物中寻找已灭绝生命痕迹的可能性。顺磁自由基自然存在于前寒武纪燧石中碳化无定形碳质物质中，被用作局部结构探针，并通过电子顺磁共振（EPR）光谱进行研究。通过监测脉冲 EPR 中电子自旋回波的核调制，检测到这些自由基内部和周围元素的核磁共振跃迁。我们发现，年龄高达 35 亿年的微生物化石中的碳质物质给出了氢（¹H）、碳（¹³C）和磷（³¹P）核的特定核磁共振特征。我们观察到，这些已灭绝生命的潜在生物特征既不存在于碳质陨石（45.6 亿年）的碳质物质中，也不存在于任何源自有机和生物有机前体碳化的碳质物质中。这些结果表明，这些核特征对热事件敏感，可用于变质程度不高于绿片岩相的太古代燧石。
