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      Shock-transformation of whitlockite to merrillite and the implications for meteoritic phosphate

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          Abstract

          Meteorites represent the only samples available for study on Earth of a number of planetary bodies. The minerals within meteorites therefore hold the key to addressing numerous questions about our solar system. Of particular interest is the Ca-phosphate mineral merrillite, the anhydrous end-member of the merrillite–whitlockite solid solution series. For example, the anhydrous nature of merrillite in Martian meteorites has been interpreted as evidence of water-limited late-stage Martian melts. However, recent research on apatite in the same meteorites suggests higher water content in melts. One complication of using meteorites rather than direct samples is the shock compression all meteorites have experienced, which can alter meteorite mineralogy. Here we show whitlockite transformation into merrillite by shock-compression levels relevant to meteorites, including Martian meteorites. The results open the possibility that at least part of meteoritic merrillite may have originally been H +-bearing whitlockite with implications for interpreting meteorites and the need for future sample return.

          Abstract

          Quantifying the amount of water in meteorites remains challenging, with minerals the key to understanding water contents. Here, Adcock et al. perform shock experiments on H +-bearing whitlockite demonstrating that it may transform into anhydrous merrillite, which is commonly found in Martian meteorites.

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          Synthesis of activated pyrimidine ribonucleotides in prebiotically plausible conditions.

          At some stage in the origin of life, an informational polymer must have arisen by purely chemical means. According to one version of the 'RNA world' hypothesis this polymer was RNA, but attempts to provide experimental support for this have failed. In particular, although there has been some success demonstrating that 'activated' ribonucleotides can polymerize to form RNA, it is far from obvious how such ribonucleotides could have formed from their constituent parts (ribose and nucleobases). Ribose is difficult to form selectively, and the addition of nucleobases to ribose is inefficient in the case of purines and does not occur at all in the case of the canonical pyrimidines. Here we show that activated pyrimidine ribonucleotides can be formed in a short sequence that bypasses free ribose and the nucleobases, and instead proceeds through arabinose amino-oxazoline and anhydronucleoside intermediates. The starting materials for the synthesis-cyanamide, cyanoacetylene, glycolaldehyde, glyceraldehyde and inorganic phosphate-are plausible prebiotic feedstock molecules, and the conditions of the synthesis are consistent with potential early-Earth geochemical models. Although inorganic phosphate is only incorporated into the nucleotides at a late stage of the sequence, its presence from the start is essential as it controls three reactions in the earlier stages by acting as a general acid/base catalyst, a nucleophilic catalyst, a pH buffer and a chemical buffer. For prebiotic reaction sequences, our results highlight the importance of working with mixed chemical systems in which reactants for a particular reaction step can also control other steps.
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            DIOPTAS: a program for reduction of two-dimensional X-ray diffraction data and data exploration

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              Hugoniot equation of state of twelve rocks

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                Author and article information

                Journal
                Nat Commun
                Nat Commun
                Nature Communications
                Nature Publishing Group
                2041-1723
                06 March 2017
                2017
                : 8
                Affiliations
                [1 ]Department of Geoscience, University of Nevada, Las Vegas , 4505 South Maryland Parkway, Las Vegas, Nevada 89154, USA
                [2 ]High Pressure Science and Engineering Center, University of Nevada, Las Vegas, 4505 South Maryland Parkway , Las Vegas, Nevada 89154, USA
                [3 ]LSPM-CNRS, Institut Galilée , Université Paris 13, Nord, 99, av. J. B. Clément, 93430 Villetaneuse, France
                [4 ]Key Laboratory of Advanced Technologies of Materials, Ministry of Education, Southwest Jiaotong University , Chengdu, Sichuan 610031, China
                [5 ]The Peac Institute of Multiscale Sciences , Chengdu, Sichuan 610031, China
                [6 ]CAS Key Laboratory of Materials Behavior and Design, Department of Modern Mechanics, University of Science and Technology of China , Hefei, Anhui 230027, China
                [7 ]GeoScienceEnviro Center for Advanced Radiation Sources, University of Chicago, Advanced Photon Source, Argonne National Laboratory , Argonne, Illinois 60439, USA
                [8 ]Lawrence Berkeley National Laboratory, Advanced Light Source, University of California, Berkeley , Berkeley, California 94720, USA
                [9 ]High Pressure Collaborative Access Team (HPCAT), Geophysical Laboratory, Carnegie Institution of Washington , Argonne, Illinois 60439, USA
                Author notes
                [*]

                These authors contributed equally to this work.

                Article
                ncomms14667
                10.1038/ncomms14667
                5343502
                28262701
                Copyright © 2017, The Author(s)

                This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article's Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

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