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  1 / 1004 MEDLINE  
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[PMID]:28001448
[Au] Autor:Ziurys LM; Halfen DT; Geppert W; Aikawa Y
[Ad] Endereço:1 Department of Chemistry and Biochemistry, Department of Astronomy, and Arizona Radio Observatory, University of Arizona , Tucson, Arizona, USA .
[Ti] Título:Following the Interstellar History of Carbon: From the Interiors of Stars to the Surfaces of Planets.
[So] Source:Astrobiology;16(12):997-1012, 2016 Dec.
[Is] ISSN:1557-8070
[Cp] País de publicação:United States
[La] Idioma:eng
[Ab] Resumo:The chemical history of carbon is traced from its origin in stellar nucleosynthesis to its delivery to planet surfaces. The molecular carriers of this element are examined at each stage in the cycling of interstellar organic material and their eventual incorporation into solar system bodies. The connection between the various interstellar carbon reservoirs is also examined. Carbon has two stellar sources: supernova explosions and mass loss from evolved stars. In the latter case, the carbon is dredged up from the interior and then ejected into a circumstellar envelope, where a rich and unusual C-based chemistry occurs. This molecular material is eventually released into the general interstellar medium through planetary nebulae. It is first incorporated into diffuse clouds, where carbon is found in polyatomic molecules such as H CO, HCN, HNC, c-C H , and even C . These objects then collapse into dense clouds, the sites of star and planet formation. Such clouds foster an active organic chemistry, producing compounds with a wide range of functional groups with both gas-phase and surface mechanisms. As stars and planets form, the chemical composition is altered by increasing stellar radiation, as well as possibly by reactions in the presolar nebula. Some molecular, carbon-rich material remains pristine, however, encapsulated in comets, meteorites, and interplanetary dust particles, and is delivered to planet surfaces. Key Words: Carbon isotopes-Prebiotic evolution-Interstellar molecules-Comets-Meteorites. Astrobiology 16, 997-1012.
[Mh] Termos MeSH primário: Carbono/análise
Planetas
Astros Celestes/química
[Mh] Termos MeSH secundário: Poeira Cósmica/análise
Meteoroides
[Pt] Tipo de publicação:JOURNAL ARTICLE; REVIEW
[Nm] Nome de substância:
0 (Cosmic Dust); 7440-44-0 (Carbon)
[Em] Mês de entrada:1709
[Cu] Atualização por classe:170929
[Lr] Data última revisão:
170929
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:161222
[St] Status:MEDLINE
[do] DOI:10.1089/ast.2016.1484


  2 / 1004 MEDLINE  
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[PMID]:27882988
[Au] Autor:Witze A
[Ti] Título:Rock core from dinosaur-killing impact reveals how enormous craters form.
[So] Source:Nature;539(7630):478, 2016 11 24.
[Is] ISSN:1476-4687
[Cp] País de publicação:England
[La] Idioma:eng
[Mh] Termos MeSH primário: Dinossauros
Meteoroides
[Mh] Termos MeSH secundário: Animais
Terra (Planeta)
Homicídio
[Pt] Tipo de publicação:NEWS; COMMENT
[Em] Mês de entrada:1612
[Cu] Atualização por classe:170220
[Lr] Data última revisão:
170220
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:161125
[St] Status:MEDLINE
[do] DOI:10.1038/nature.2016.20994


  3 / 1004 MEDLINE  
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[PMID]:27827540
[Au] Autor:Pearce BK; Pudritz RE
[Ad] Endereço:Origins Institute and Department of Physics and Astronomy, McMaster University , Hamilton, Canada .
[Ti] Título:Meteorites and the RNA World: A Thermodynamic Model of Nucleobase Synthesis within Planetesimals.
[So] Source:Astrobiology;16(11):853-872, 2016 Nov.
[Is] ISSN:1557-8070
[Cp] País de publicação:United States
[La] Idioma:eng
[Ab] Resumo:The possible meteorite parent body origin of Earth's pregenetic nucleobases is substantiated by the guanine (G), adenine (A), and uracil (U) measured in various meteorites. Cytosine (C) and thymine (T), however, are absent in meteorites, making the emergence of an RNA and later RNA/DNA/protein world problematic. We investigated the meteorite parent body (planetesimal) origin of all nucleobases by computationally modeling 18 reactions that potentially contribute to nucleobase formation in such environments. Out of this list, we identified the two most important reactions for each nucleobase and found that these involve small molecules such as HCN, CO, NH , and water that ultimately arise from the protoplanetary disks in which planetesimals are built. The primary result of this study is that cytosine is unlikely to persist within meteorite parent bodies due to aqueous deamination. Thymine has a thermodynamically favorable reaction pathway from uracil, formaldehyde, and formic acid but likely did not persist within planetesimals containing H O due to an oxidation reaction with this molecule. Finally, while Fischer-Tropsch (FT) synthesis is found to be the dominant source of nucleobases within our model planetesimal, non-catalytic (NC) synthesis may still be significant under certain chemical conditions (e.g., within CR2 parent bodies). We discuss several major consequences of our results for the origin of the RNA world. Key Words: Astrobiology-Cosmochemistry-Meteorites-RNA world-Abiotic organic synthesis. Astrobiology 16, 853-872.
[Mh] Termos MeSH primário: Meteoroides
Modelos Teóricos
Planetas
RNA/química
[Mh] Termos MeSH secundário: Pressão
Purinas/análise
Pirimidinas/análise
Termodinâmica
[Pt] Tipo de publicação:JOURNAL ARTICLE
[Nm] Nome de substância:
0 (Purines); 0 (Pyrimidines); 63231-63-0 (RNA)
[Em] Mês de entrada:1709
[Cu] Atualização por classe:170929
[Lr] Data última revisão:
170929
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:161110
[St] Status:MEDLINE


  4 / 1004 MEDLINE  
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[PMID]:27708332
[Au] Autor:Gibney E
[Ti] Título:Mission accomplished: Rosetta crashes into comet.
[So] Source:Nature;538(7623):13-14, 2016 10 06.
[Is] ISSN:1476-4687
[Cp] País de publicação:England
[La] Idioma:eng
[Mh] Termos MeSH primário: Meteoroides
Voo Espacial/instrumentação
Astronave
[Mh] Termos MeSH secundário: Europa (Continente)
Meio Ambiente Extraterreno/química
Nitrogênio/análise
Oxigênio/análise
Fotografia
Água/análise
Água/química
[Pt] Tipo de publicação:NEWS
[Nm] Nome de substância:
059QF0KO0R (Water); N762921K75 (Nitrogen); S88TT14065 (Oxygen)
[Em] Mês de entrada:1611
[Cu] Atualização por classe:161230
[Lr] Data última revisão:
161230
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:161007
[St] Status:MEDLINE
[do] DOI:10.1038/nature.2016.20705


  5 / 1004 MEDLINE  
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[PMID]:27629643
[Au] Autor:Burkhardt C; Borg LE; Brennecka GA; Shollenberger QR; Dauphas N; Kleine T
[Ad] Endereço:Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, 5734 South Ellis Avenue, Chicago, Illinois 60637, USA.
[Ti] Título:A nucleosynthetic origin for the Earth's anomalous (142)Nd composition.
[So] Source:Nature;537(7620):394-8, 2016 09 15.
[Is] ISSN:1476-4687
[Cp] País de publicação:England
[La] Idioma:eng
[Ab] Resumo:A long-standing paradigm assumes that the chemical and isotopic compositions of many elements in the bulk silicate Earth are the same as in chondrites. However, the accessible Earth has a greater (142)Nd/(144)Nd ratio than do chondrites. Because (142)Nd is the decay product of the now-extinct (146)Sm (which has a half-life of 103 million years), this (142)Nd difference seems to require a higher-than-chondritic Sm/Nd ratio for the accessible Earth. This must have been acquired during global silicate differentiation within the first 30 million years of Solar System formation and implies the formation of a complementary (142)Nd-depleted reservoir that either is hidden in the deep Earth, or lost to space by impact erosion. Whether this complementary reservoir existed, and whether or not it has been lost from Earth, is a matter of debate, and has implications for determining the bulk composition of Earth, its heat content and structure, as well as for constraining the modes and timescales of its geodynamical evolution. Here we show that, compared with chondrites, Earth's precursor bodies were enriched in neodymium that was produced by the slow neutron capture process (s-process) of nucleosynthesis. This s-process excess leads to higher (142)Nd/(144)Nd ratios; after correction for this effect, the (142)Nd/(144)Nd ratios of chondrites and the accessible Earth are indistinguishable within five parts per million. The (142)Nd offset between the accessible silicate Earth and chondrites therefore reflects a higher proportion of s-process neodymium in the Earth, and not early differentiation processes. As such, our results obviate the need for hidden-reservoir or super-chondritic Earth models and imply a chondritic Sm/Nd ratio for the bulk Earth. Although chondrites formed at greater heliocentric distances and contain a different mix of presolar components than Earth, they nevertheless are suitable proxies for Earth's bulk chemical composition.
[Mh] Termos MeSH primário: Terra (Planeta)
Evolução Planetária
[Mh] Termos MeSH secundário: Meia-Vida
Meteoroides
Sistema Solar
[Pt] Tipo de publicação:COMMENT; LETTER
[Em] Mês de entrada:1609
[Cu] Atualização por classe:170922
[Lr] Data última revisão:
170922
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:160916
[St] Status:MEDLINE
[do] DOI:10.1038/nature18956


  6 / 1004 MEDLINE  
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[PMID]:27582215
[Au] Autor:Kolokolova L
[Ad] Endereço:Department of Astronomy, University of Maryland, College Park, Maryland 20742, USA.
[Ti] Título:Planetary science: Cometary dust under the microscope.
[So] Source:Nature;537(7618):37-8, 2016 09 01.
[Is] ISSN:1476-4687
[Cp] País de publicação:England
[La] Idioma:eng
[Mh] Termos MeSH primário: Poeira
Planetas
[Mh] Termos MeSH secundário: Meio Ambiente Extraterreno
Meteoroides
[Pt] Tipo de publicação:COMMENT; JOURNAL ARTICLE
[Nm] Nome de substância:
0 (Dust)
[Em] Mês de entrada:1609
[Cu] Atualização por classe:170220
[Lr] Data última revisão:
170220
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:160902
[St] Status:MEDLINE
[do] DOI:10.1038/537037a


  7 / 1004 MEDLINE  
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[PMID]:27532050
[Au] Autor:Osinski GR; Ferrière L
[Ad] Endereço:Centre for Planetary Science and Exploration, University of Western Ontario, 1151 Richmond Street, London, Ontario N6A 5B7, Canada.; Department of Earth Sciences and Department of Physics and Astronomy, University of Western Ontario, London, Ontario N6A 5B7, Canada.
[Ti] Título:Shatter cones: (Mis)understood?
[So] Source:Sci Adv;2(8):e1600616, 2016 08.
[Is] ISSN:2375-2548
[Cp] País de publicação:United States
[La] Idioma:eng
[Ab] Resumo:Meteorite impact craters are one of the most common geological features in the solar system. An impact event is a near-instantaneous process that releases a huge amount of energy over a very small region on a planetary surface. This results in characteristic changes in the target rocks, from vaporization and melting to solid-state effects, such as fracturing and shock metamorphism. Shatter cones are distinctive striated conical fractures that are considered unequivocal evidence of impact events. They are one of the most used and trusted shock-metamorphic effects for the recognition of meteorite impact structures. Despite this, there is still considerable debate regarding their formation. We show that shatter cones are present in several stratigraphic settings within and around impact structures. Together with the occurrence of complete and "double" cones, our observations are most consistent with shatter cone formation due to tensional stresses generated by scattering of the shock wave due to heterogeneities in the rock. On the basis of field mapping, we derive the relationship D sc = 0.4 D a, where D sc is the maximum spatial extent of in situ shatter cones, and D a is the apparent crater diameter. This provides an important, new, more accurate method to estimate the apparent diameter of eroded complex craters on Earth. We have reestimated the diameter of eight well-known impact craters as part of this study. Finally, we suggest that shatter cones may reduce the strength of the target, thus aiding crater collapse, and that their distribution in central uplifts also records the obliquity of impact.
[Mh] Termos MeSH primário: Evolução Planetária
Meteoroides
Planetas
Sistema Solar
[Mh] Termos MeSH secundário: Terra (Planeta)
Meio Ambiente Extraterreno
Fenômenos Geológicos
[Pt] Tipo de publicação:JOURNAL ARTICLE; RESEARCH SUPPORT, NON-U.S. GOV'T
[Em] Mês de entrada:1707
[Cu] Atualização por classe:170731
[Lr] Data última revisão:
170731
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:160818
[St] Status:MEDLINE
[do] DOI:10.1126/sciadv.1600616


  8 / 1004 MEDLINE  
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[PMID]:27419237
[Au] Autor:Marrocchi Y; Chaussidon M; Piani L; Libourel G
[Ad] Endereço:Centre de Recherches Pétrographiques et Géochimiques, CNRS, Université de Lorraine, UMR 7358, 54501 Vandoeuvre-lès-Nancy, France.
[Ti] Título:Early scattering of the solar protoplanetary disk recorded in meteoritic chondrules.
[So] Source:Sci Adv;2(7):e1601001, 2016 07.
[Is] ISSN:2375-2548
[Cp] País de publicação:United States
[La] Idioma:eng
[Ab] Resumo:Meteoritic chondrules are submillimeter spherules representing the major constituent of nondifferentiated planetesimals formed in the solar protoplanetary disk. The link between the dynamics of the disk and the origin of chondrules remains enigmatic. Collisions between planetesimals formed at different heliocentric distances were frequent early in the evolution of the disk. We show that the presence, in some chondrules, of previously unrecognized magnetites of magmatic origin implies the formation of these chondrules under impact-generated oxidizing conditions. The three oxygen isotopes systematic of magmatic magnetites and silicates can only be explained by invoking an impact between silicate-rich and ice-rich planetesimals. This suggests that these peculiar chondrules are by-products of the early mixing in the disk of populations of planetesimals from the inner and outer solar system.
[Mh] Termos MeSH primário: Meteoroides
Sistema Solar
[Mh] Termos MeSH secundário: Magnetismo
Isótopos de Oxigênio/química
Silicatos/química
Sulfetos/química
Isótopos de Enxofre/química
[Pt] Tipo de publicação:JOURNAL ARTICLE; RESEARCH SUPPORT, NON-U.S. GOV'T
[Nm] Nome de substância:
0 (Oxygen Isotopes); 0 (Silicates); 0 (Sulfides); 0 (Sulfur Isotopes)
[Em] Mês de entrada:1705
[Cu] Atualização por classe:170504
[Lr] Data última revisão:
170504
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:160716
[St] Status:MEDLINE
[do] DOI:10.1126/sciadv.1601001


  9 / 1004 MEDLINE  
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[PMID]:27418500
[Au] Autor:Rosen J
[Ad] Endereço:Julia Rosen is a freelance writer in Portland, Oregon.
[Ti] Título:Thinking the Unthinkable.
[So] Source:Science;353(6296):232-7, 2016 Jul 15.
[Is] ISSN:1095-9203
[Cp] País de publicação:United States
[La] Idioma:eng
[Mh] Termos MeSH primário: Desastres
[Mh] Termos MeSH secundário: Planejamento em Desastres
Desastres/prevenção & controle
Desastres/estatística & dados numéricos
Terremotos
Meteoroides
Energia Solar
Pensamento
Erupções Vulcânicas
[Pt] Tipo de publicação:NEWS
[Em] Mês de entrada:1610
[Cu] Atualização por classe:161230
[Lr] Data última revisão:
161230
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:160716
[St] Status:MEDLINE
[do] DOI:10.1126/science.353.6296.232


  10 / 1004 MEDLINE  
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[PMID]:27391147
[Au] Autor:Holliday V; Surovell T; Johnson E
[Ad] Endereço:School of Anthropology & Department of Geosciences, University of Arizona, Tucson, Arizona, United States of America.
[Ti] Título:A Blind Test of the Younger Dryas Impact Hypothesis.
[So] Source:PLoS One;11(7):e0155470, 2016.
[Is] ISSN:1932-6203
[Cp] País de publicação:United States
[La] Idioma:eng
[Ab] Resumo:The Younger Dryas Impact Hypothesis (YDIH) states that North America was devastated by some sort of extraterrestrial event ~12,800 calendar years before present. Two fundamental questions persist in the debate over the YDIH: Can the results of analyses for purported impact indicators be reproduced? And are the indicators unique to the lower YD boundary (YDB), i.e., ~12.8k cal yrs BP? A test reported here presents the results of analyses that address these questions. Two different labs analyzed identical splits of samples collected at, above, and below the ~12.8ka zone at the Lubbock Lake archaeological site (LL) in northwest Texas. Both labs reported similar variation in levels of magnetic micrograins (>300 mg/kg >12.8ka and <11.5ka, but <150 mg/kg 12.8ka to 11.5ka). Analysis for magnetic microspheres in one split, reported elsewhere, produced very low to nonexistent levels throughout the section. In the other split, reported here, the levels of magnetic microspherules and nanodiamonds are low or nonexistent at, below, and above the YDB with the notable exception of a sample <11,500 cal years old. In that sample the claimed impact proxies were recovered at abundances two to four orders of magnitude above that from the other samples. Reproducibility of at least some analyses are problematic. In particular, no standard criteria exist for identification of magnetic spheres. Moreover, the purported impact proxies are not unique to the YDB.
[Mh] Termos MeSH primário: Arqueologia
Sedimentos Geológicos/análise
Geologia
[Mh] Termos MeSH secundário: Geografia
Lagos
Magnetismo
Meteoroides
Nanodiamantes
América do Norte
Fenômenos Físicos
Reprodutibilidade dos Testes
Texas
[Pt] Tipo de publicação:JOURNAL ARTICLE
[Nm] Nome de substância:
0 (Nanodiamonds)
[Em] Mês de entrada:1707
[Cu] Atualização por classe:170731
[Lr] Data última revisão:
170731
[Sb] Subgrupo de revista:IM
[Da] Data de entrada para processamento:160709
[St] Status:MEDLINE
[do] DOI:10.1371/journal.pone.0155470



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