The Origin of Nitrogen on Earth: Implications from Isotope and Petrologic Studies of Planetary Materials at the Sub-Micrometer Scale.

地球上氮的起源：亚微米尺度行星材料同位素和岩石学研究的意义。

• 批准号: 276812115
• 负责人: Dr. Jan Leitner
• 金额: --
• 依托单位: Institut für Geowissenschaften
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2015
• 资助国家: 德国
• 起止时间: 2014-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/276812115?language=en
• 关键词: Origin; Nitrogen; Earth; Implications; Isotope

Nitrogen, the most abundant component in Earth’s atmosphere, was a key element for the evolution of Earth’s biosphere. The respective isotopic compositions of the rocky planets Earth, Mars and Venus differ from those of the Sun and the Protosolar Nebula (PSN). Thus, other components from the solar nebula must have significantly contributed to terrestrial nitrogen. Isotopic signatures of the enstatite chondrites (ECs) suggest them as the best analogue material for the building blocks of the primordial Earth, together with a smaller fraction of ordinary chondrite and carbonaceous chondrite material. Model calculations from other studies consider angrites, a group of achondrites, as best fit. Bulk chemistry indicates that our sample set of Solar System materials is far from complete, with a significant portion contributing to Earth missing from the meteorite record. This emphasizes the necessity to characterize the inventory of nitrogen-bearing phases in the available sets of meteoritic samples, to allow predictions about the missing fraction. During the first period of this project, it became evident that the known N-carriers in the ECs cannot account for the total amount of bulk nitrogen, indicating other phases as host materials. Organic material (OM) in several carbonaceous chondrites contained high enrichments in 15N compared to the terrestrial atmosphere. These enrichments were the result of fluid interaction on the meteoritic parent body, and not directly inherited from the protosolar cloud. Investigation of the chemical functionalities of these materials is still in progress, but one of the implications of this observation is that the chondritic organic material that contributed nitrogen to the primordial Earth might span an even wider (structural and chemical) range than initially anticipated. I will continue the investigation of nitrogen-bearing materials in various chondritic meteorites, with the main focus on metal, sulfides, and silicates in ECs. In addition, the quantification of the anorganic N-carriers in enstatite and ordinary chondrites will be continued, and the OM inventory of CO and CV chondrites will be studied. The sample set will be expanded to achondrites that have potential relations to the terrestrial building blocks. Sample characterization will be carried out by SEM and SEM-EDS. N-isotopic investigations will be conducted by NanoSIMS. Nitrogen is typically detected with SIMS as CN-, which normally restricts conventional N-isotopic measurements to phases that also contain carbon. Thus, some samples will be prepared by C-impregnation to enhance the CN-yield. The N isotopes of C-free phases can also be studied by using 14,15N+. Samples will be selected and prepared for structural analysis by transmission electron microscopy. This project will expand the inventory of N-bearing phases and their N-isotopic compositions, which ultimately will help to determine the nature of the carriers contributing to Earth’s nitrogen.

氮是地球大气中最丰富的成分，是地球生物圈演化的关键元素。岩石行星地球、火星和金星各自的同位素组成与太阳和原太阳星云（PSN）的同位素组成不同。因此，来自太阳星云的其他成分一定对地球上的氮有很大的贡献。顽火辉石球粒陨石（ECs）的同位素特征表明，它们是原始地球构建块的最佳模拟材料，以及较小比例的普通球粒陨石和碳质球粒陨石材料。其他研究的模型计算认为安杰利特，一组无球粒陨石，是最合适的。大量化学物质表明，我们的太阳系材料样本集还远远不完整，其中很大一部分是地球在陨石记录中缺失的。这强调了有必要描述现有陨石样品中含氮相的清单，以预测缺失的部分。在该项目的第一阶段，很明显，EC中已知的N-载体不能解释散装氮的总量，表明其他阶段作为主体材料。与陆地大气相比，几种碳质玄武岩中的有机物质（OM）在15 N中的富集程度较高。这些富集是陨石母体上流体相互作用的结果，而不是直接继承自原太阳云。对这些物质的化学功能的研究仍在进行中，但这一观察的影响之一是，为原始地球贡献氮的南极有机物质可能跨越比最初预期的更宽的（结构和化学）范围。我将继续研究各种南极陨石中的含氮物质，主要关注EC中的金属、硫化物和硅酸盐。此外，将继续对顽火辉石和普通顽火辉石中的无机氮载体进行定量，并将研究CO和CV顽火辉石的OM清单。样本集将扩大到与陆地建筑块有潜在关系的无球粒陨石。将通过SEM和SEM-EDS进行样品表征。将通过NanoSIMS进行N-同位素研究。氮通常用西姆斯检测为CN-，这通常将传统的N-同位素测量限制在也含有碳的相。因此，将通过C-浸渍制备一些样品以提高CN-产率。无碳相的N同位素也可以用14，15 N+来研究。选择并制备样品，通过透射电子显微镜进行结构分析。该项目将扩大含氮相及其氮同位素组成的清单，最终将有助于确定地球氮载体的性质。