Isotope analysis extraterrestrial samples

This chapter provides an overview of the impact that MC-ICP-MS has had on cosmochemical research. To this end, it encompasses (i) an introduction to the extraterrestrial samples, and in particular meteorites, which are analyzed (ii) a brief explanation of the origin and significance of the most important types of isotopic anomalies that are measured (iii) a brief introduction to the particular advantages that MC-ICP-MS provides for isotopic analysis in cosmochemistry and to common analytical procedures and (iv) an overview of important applications of MC-ICP-MS in cosmochemistry. This last section highlights selected novel findings and their scientific significance, while also discussing particular analytical procedures and potential pitfalls. 

Although chemical and isotopic analysis by remote sensing using either Earth- or satellite-based instruments play an important role in some cosmochemical studies, laboratory measurements on real samples remain the predominant means of data acquisition. In cosmochemistry, extraterrestrial materials are the most... 

Dynamic SIMS is used for depth profile analysis of mainly inorganic samples. The objective is to measure the distribution of a certain compound as a function of depth. At best the resolution in this direction is < 1 nm, that is, considerably better than the lateral resolution. Depth profiling of semiconductors is used, for example, to monitor trace level elements or to measure the sharpness of the interface between two layers of different composition. For glass it is of interest to investigate slow processes such as corrosion, and small particle analyses include environmental samples contaminated by radioisotopes and isotope characterization in extraterrestrial dust. 

An alternative to the terrestrial synthesis of the nucleobases is to invoke interstellar chemistry. Martins has shown, using an analysis of the isotopic abundance of 13C, that a sample of the 4.6 billion year old Murchison meteorite which fell in Australia in 1969 contains traces of uracil and a pyrimidine derivative, xanthine. Samples of soil that surrounded the meteor when it was retrieved were also analyzed. They gave completely different results for uracil, consistent with its expected terrestrial origin, and xanthine was undetectable [48], The isotopic distributions of carbon clearly ruled out terrestrial contamination as a source of the organic compounds present in the meteorite. At 0°C and neutral pH cytosine slowly decomposes to uracil and guanine decomposes to xanthine so both compounds could be the decomposition products of DNA or RNA nucleobases. They must have either travelled with the meteorite from its extraterrestrial origin or been formed from components present in the meteorite and others encountered on its journey to Earth. Either way, delivery of nucleobases to a prebiotic Earth could plausibly have been undertaken by meteors. The conditions that formed the bases need not have been those of an early Earth at all but of a far more hostile environment elsewhere in the Solar System. That environment may have been conducive to the production of individual bases but they may never have been able to form stable DNA or RNA polymers this development may have required the less extreme conditions prevalent on Earth. 

Analysis of extraterrestrial materials, and in particular meteorites, is an important focus of cosmochemical research, as such samples preserve chemical and isotopic records of early solar system conditions and processes. The first studies of meteorites, which recognized that such samples have an extraterrestrial origin, date back to the late eighteenth century [3], but modem research in cosmochemistry has a much more recent origin. This is traced back by many to the founder of contemporary geochemistry, V.M. Goldschmidt, as he produced early, but well-founded, compilations of cosmic element abundances, based on data acquired for meteorites [4, 5]. Goldschmidt s work was later continued and extended by Suess in collaboration with Urey and their study on the abundances of the elements [5] is still an important milestone in cosmochemistry. 

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