¹D. H. Wooden, ²H. A. Ishii, ³M. E. Zolensky
Philosophical Transactions of the Royal Society A 375, 2097 Link to Article [https://doi.org/10.1098/rsta.2016.0260]
¹NASA Ames Research Center, Moffett Field, CA 94035-0001, USA
²University of Hawaii, Hawai’i Institute of Geophysics and Planetology, Honolulu, HI 96822, USA
³NASA Johnson Space Center, ARES, X12 2010 NASA Parkway, Houston, TX 77058-3607, USA
e-mail: diane.wooden@nasa.gov

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^1,2Hidenori Genda, ²Tsuyoshi Iizuka, ^3,4Takanori Sasaki, ^1,4Yuichiro Ueno, ^2,5Masahiro Ikoma
Earth and Planetary Science Letters 470, 87-95 Link to Article [https://doi.org/10.1016/j.epsl.2017.04.035]
¹Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan
²Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
³Department of Astronomy, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan
⁴Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan
⁵Research Center for the Early Universe, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
Copyright Elsevier

The Earth was born in violence. Many giant collisions of protoplanets are thought to have occurred during the terrestrial planet formation. Here we investigated the giant impact stage by using a hybrid code that consistently deals with the orbital evolution of protoplanets around the Sun and the details of processes during giant impacts between two protoplanets. A significant amount of materials (up to several tens of percent of the total mass of the protoplanets) is ejected by giant impacts. We call these ejected fragments the giant-impact fragments (GIFs). In some of the erosive hit-and-run and high-velocity collisions, metallic iron is also ejected, which comes from the colliding protoplanets’ cores. From ten numerical simulations for the giant impact stage, we found that the mass fraction of metallic iron in GIFs ranges from ∼1 wt% to ∼25 wt%. We also discussed the effects of the GIFs on the dynamical and geochemical characteristics of formed terrestrial planets. We found that the GIFs have the potential to solve the following dynamical and geochemical conflicts: (1) The Earth, currently in a near circular orbit, is likely to have had a highly eccentric orbit during the giant impact stage. The GIFs are large enough in total mass to lower the eccentricity of the Earth to its current value via their dynamical friction. (2) The concentrations of highly siderophile elements (HSEs) in the Earth’s mantle are greater than what was predicted experimentally. Re-accretion of the iron-bearing GIFs onto the Earth can contribute to the excess of HSEs. In addition, Iron-bearing GIFs provide significant reducing agent that could transform primitive CO2–H2O atmosphere and ocean into more reducing H2-bearing atmosphere. Thus, GIFs are important for the origin of Earth’s life and its early evolution.

¹S.L. Simpson, ²A.J. Boyce, ³P. Lambert, ¹P. Lindgren, ¹M.R. Lee
Earth and Planetary Science Letters 460, 192-200 Link to Article [https://doi.org/10.1016/j.epsl.2016.12.023]
¹University of Glasgow, School of Geographical and Earth Sciences, Lilybank Gardens, G12 8QQ, Glasgow, UK
²Scottish Universities Environmental Research Centre, Rankine Ave, East Kilbride, G75 0QF, Glasgow, UK
³Sciences et Applications, 218 Boulevard Albert 1er, 33800 Bordeaux, France
Copyright Elsevier

The highly eroded 23 km diameter Rochechouart impact structure, France, has extensive evidence for post-impact hydrothermal alteration and sulphide mineralisation. The sulphides can be divided into four types on the basis of their mineralogy and host rock. They range from pyrites and chalcopyrite in the underlying coherent crystalline basement to pyrites hosted in the impactites. Sulphur isotopic results show that δ34S values vary over a wide range, from −35.8‰ to +0.4‰. The highest values, δ34S −3.7‰ to +0.4‰, are recorded in the coherent basement, and likely represent a primary terrestrial sulphur reservoir. Sulphides with the lowest values, δ34S −35.8‰ to −5.2‰, are hosted within locally brecciated and displaced parautochthonous and autochthonous impactites. Intermediate δ34S values of −10.7‰ to −1.2‰ are recorded in the semi-continuous monomict lithic breccia unit, differing between carbonate-hosted sulphides and intraclastic and clastic matrix-hosted sulphides. Such variable isotope values are consistent with a biological origin, via bacterial sulphate reduction, for sulphides in the parautochthonous and autochthonous units; these minerals formed in the shallow subsurface and are probably related to the post impact hydrothermal system. The source of the sulphate is likely to have been seawater, penecontemporaneous to the impact, as inferred from the marginal marine paleogeography of the structure. In other eroded impact craters that show evidence for impact-induced hydrothermal circulation, indirect evidence for life may be sought isotopically within late-stage (≤120 °C) secondary sulphides and within the shocked and brecciated basement immediately beneath the transient crater floor.

¹Michael E. Zolensky, ²Robert J. Bodnar, ³Hisayoshi Yurimoto, ⁴Shoichi Itoh, ¹Marc Fries, ⁵Andrew Steele,¹ Queenie H.-S. Chan, ⁴Akira Tsuchiyama, ⁶Yoko Kebukawa, ⁷Motoo Ito
Philosophical Transactions of the Royal Society A Link to Article [https://doi.org/10.1098/rsta.2015.0386]
¹ARES, NASA Johnson Space Center, Houston, TX 77058, USA
²Fluids Research Laboratory, Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
³Department of Natural History Sciences, Hokkaido University, Kita-10 Nishi-8 Kita-ku, Sapporo 060-0810, Japan and ISAS, JAXA, Chuo-ku, Sagamihara, Kanagawa 252-5210, Japan
⁴Graduate School of Science, Kyoto University, Kitashirakawaoiwakecho, Sakyo-ku, Kyoto 606-8502, Japan
⁵Geophysical Laboratory, Carnegie Institution for Science, Washington, DC 20005, USA
⁶Faculty of Engineering, Yokohama National University, 79-1 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan
⁷Kochi Institute for Core Sample Research, JAMSTEC, B200 Monobe Otsu, Nankoku, Kochi 783-8502, Japan

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Hejiu Hui et al. (>10)*
Earth and Planetary Science Letters 473, 14-23 Link to Article [https://doi.org/10.1016/j.epsl.2017.05.029]
¹State Key Laboratory for Mineral Deposits Research & Lunar and Planetary Science Institute, School of Earth Sciences and Engineering, Nanjing University, Nanjing, Jiangsu 210023, China
²Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, IN 46556, USA
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Copyright Elsevier

Knowing the amount and timing of water incorporation into the Moon has fundamental implications for our understanding of how the Earth–Moon system formed. Water has been detected in lunar samples but its abundance, distribution and origin are debated. To address these issues, we report water concentrations and hydrogen isotope ratios obtained by secondary ion mass spectrometry (SIMS) of plagioclase from ferroan anorthosites (FANs), the only available lithology thought to have crystallized directly from the lunar magma ocean (LMO). The measured water contents are consistent with previous results by Fourier transform infrared spectroscopy (FTIR). Combined with literature data, δD values of lunar igneous materials least-degassed at the time of their crystallization range from −280 to +310‰, the latter value being that of FAN 60015 corrected for cosmic ray exposure. We interpret these results as hydrogen isotopes being fractionated during degassing of molecular hydrogen (H2) in the LMO, starting with the magmatic δD value of primordial water at the beginning of LMO being about −280‰, evolving to about +310‰ at the time of anorthite crystallization, i.e. during the formation of the primary lunar crust. The degassing of hydrogen in the LMO is consistent with those of other volatile elements. The wide range of δD values observed in lunar igneous rocks could be due to either various degrees of mixing of the different mantle end members, or from a range of mantle sources that were degassed to different degrees during magma evolution. Degassing of the LMO is a viable mechanism that resulted in a heterogeneous lunar interior for hydrogen isotopes.

¹Bérengère Mougel, ^1,2Frédéric Moynier, ¹Christa Göpel, ^3,4Christian Koeberl
Earth and Planetary Science Letters 460, 105-111 Link to Article [https://doi.org/10.1016/j.epsl.2016.12.008]
¹Institut de Physique du Globe de Paris, Université Sorbonne Paris Cité, CNRS UMR 7154, Paris, France
²Institut Universitaire de France and Université Paris Diderot, Paris, France
³Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria
⁴Natural History Museum, Burgring 7, A-1010 Vienna, Austria
Copyright Elsevier

Non-mass dependent chromium isotopic signatures have been successfully used to determine the presence and identification of extra-terrestrial materials in terrestrial impact rocks. Paleoproterozoic spherule layers from Greenland (Grænsesø) and Russia (Zaonega), as well as some distal ejecta deposits (Lake Superior region) from the Sudbury impact (1849±0.3 Ma) event, have been analyzed for their Cr isotope compositions. Our results suggest that 1) these distal ejecta deposits are all of impact origin, 2) the Grænsesø and Zaonega spherule layers contain a distinct carbonaceous chondrite component, and are possibly related to the same impact event, which could be Vredefort (2023±4 Ma) or another not yet identified large impact event from that of similar age, and 3) the Sudbury ejecta record a complex meteoritic signature, which is different from the Grænsesø and Zaonega spherule layers, and could indicate the impact of a heterogeneous chondritic body.

¹Rachel L. Klima, ²Noah E. Petro
Philosophical Transactions of the Royal Astronomical Society A 375, 2094 Link to Article [https://doi.org/10.1098/rsta.2015.0391]
¹Space Exploration Sector, Planetary Exploration Group, Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, USA
²NASA Goddard Space Flight Center, Greenbelt, MD, USA

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