DOCSLIB.ORG

The Origin of Chondrules and Chondrites: Debris from Lowâ•'Velocity Impacts Between Molten Planetesimals?

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Origin of Chondrules and Chondrites: Debris from Lowâ•'Velocity Impacts Between Molten Planetesimals? Meteoritics & Planetary Science 47, Nr 12, 2170–2192 (2012) doi: 10.1111/maps.12002 The origin of chondrules and chondrites: Debris from low-velocity impacts between molten planetesimals? Ian S. SANDERS1,* and Edward R. D. SCOTT2 1Department of Geology, Trinity College, Dublin 2, Ireland 2Hawai’i Institute of Geophysics and Planetology, University of Hawai’i at Manoa, Honolulu, Hawai’i 96822, USA *Corresponding author. E-mail: [email protected] (Received 11 June 2012; revision accepted 17 September 2012) Abstract–We investigate the hypothesis that many chondrules are frozen droplets of spray from impact plumes launched when thin-shelled, largely molten planetesimals collided at low speed during accretion. This scenario, here dubbed ‘‘splashing,’’ stems from evidence that such planetesimals, intensely heated by 26Al, were abundant in the protoplanetary disk when chondrules were being formed approximately 2 Myr after calcium-aluminum-rich inclusions (CAIs), and that chondrites, far from sampling the earliest planetesimals, are made from material that accreted later, when 26Al could no longer induce melting. We show how ‘‘splashing’’ is reconcilable with many features of chondrules, including their ages, chemistry, peak temperatures, abundances, sizes, cooling rates, indented shapes, ‘‘relict’’ grains, igneous rims, and metal blebs, and is also reconcilable with features that challenge the conventional view that chondrules are flash-melted dust-clumps, particularly the high concentrations of Na and FeO in chondrules, but also including chondrule diversity, large phenocrysts, macrochondrules, scarcity of dust-clumps, and heating. We speculate that type I (FeO-poor) chondrules come from planetesimals that accreted early in the reduced, partially condensed, hot inner nebula, and that type II (FeO-rich) chondrules come from planetesimals that accreted in a later, or more distal, cool nebular setting where incorporation of water-ice with high D17O aided oxidation during heating. We propose that multiple collisions and repeated re-accretion of chondrules and other debris within restricted annular zones gave each chondrite group its distinctive properties, and led to so-called ‘‘complementarity’’ and metal depletion in chondrites. We suggest that differentiated meteorites are numerically rare compared with chondrites because their initially plentiful molten parent bodies were mostly destroyed during chondrule formation. INTRODUCTION surrounded the infant Sun, from which the planets later developed) prior to accreting to the surfaces of growing Chondrules are igneous-textured grains that make chondrite parent asteroids. They co-accreted with other up 50% or more by volume of most chondrites. Many of disk materials including small grains and droplets of them are frozen droplets of magma, typically 0.1–2 mm Fe-Ni metal and sulfide, refractory objects called across, rounded to lobate in shape, and composed largely calcium-aluminum-rich inclusions (CAIs), mineral of the Mg-rich silicate minerals olivine, (Mg,Fe)2SiO4, fragments, and dust including micron-scale grains of and pyroxene, (Mg,Fe)SiO3 (Zanda 2004; Scott and Krot stardust surviving from the presolar molecular cloud. As 2007). They tend to be either FeO-poor (type I chondrites account for five out of six meteorites falling to chondrules) or FeO-rich (type II chondrules). Their Earth, the formation of chondrules was apparently a igneous textures suggest cooling from near-liquidus process that affected a substantial fraction of the solid temperatures and solidifying over a matter of hours. material in the solar nebula. Evidently, they were present in the solar nebula, or There is no consensus on how chondrules were protoplanetary disk (the disk of gas and dust that made: two fundamentally different approaches have Ó The Meteoritical Society, 2012. 2170 Origin of chondrules and chondrites 2171 come to dominate current discussion. The first contends In this article, we examine that new picture and how that clumps of dust in the disk were transformed directly it might be extended to embrace the formation of to chondrules by rapid melting, probably as a result of chondrules and the assembly of chondritic asteroids. We shock-induced heating in the nebula. This idea was begin by showing how precise meteorite chronology now suggested half a century ago (Wood 1963, p. 165) in a indicates that planetesimals first melted long before seminal paper whose title we adopt here, and the melting chondrules were made, consistent with 26Al having been of dust-clumps, whether by shock or by some other an internal planetesimal heat source. We argue that means, has since become the prevailing theory for molten planetesimals dominated the population of chondrule formation. It has been advocated, tacitly if not bodies in the inner solar system for the first 2 Myr, and overtly, by many authors, including Taylor et al. (1983), we propose that the inevitable collisions and mergers Wood (1988), Grossman (1988), Wasson (1993), Rubin between them led to ‘‘splashing’’ with ejecta plumes (2000), Shu et al. (2001), Boss and Durisen (2005), bearing swarms of chondrule droplets and other debris, Lauretta and McSween (2006), Scott (2007), Alexander which later accreted to chondritic parent bodies. We et al. (2008), and Ruzicka et al. (2012a). evaluate the established petrographic, compositional, The second approach imagines that chondrules were and experimental evidence for chondrule formation, and produced when large volumes of molten rock became find it to be consistent with this collision scenario. splashed and dispersed into the nebula as showers of Importantly, we find some of the evidence hard to spray. Specifically, it has come to embrace a hypothesis, reconcile with the conventional view that chondrules dating from about 30 yr ago, that chondrules originated began as dust-clumps. In the last section of the article, in great plumes of droplets launched by collisions we discuss how the ‘‘splashing’’ hypothesis may relate to between planetesimals that had been intensely heated the broader picture of planetesimal evolution in the and melted by the decay of 26Al (Zook 1980, 1981; young disk, speculating on the nature of the molten Wa¨ nke et al. 1981, 1984). This second hypothesis lay precursor planetesimals, and on the origin of some dormant for many years, almost completely hitherto poorly understood features of chondrites. overshadowed by the first, and its re-awakening has been slow. Sanders (1996) attempted to revive interest, and the A NEW PARADIGM FOR CHONDRITES idea has also been promoted by LaTourrette and ANCHORED IN 26AL HEATING Wasserburg (1998), Chen et al. (1998), Lugmair and Shukolyukov (2001), and Hevey and Sanders (2006). The Conventional View of Chondrites Sanders and Taylor (2005) reviewed the hypothesis in detail. While the production of chondrules from molten Chondrites have conventionally been interpreted as planetesimals has never had a majority following, few aggregates of primitive materials that were assembled at today would dismiss it out of hand, and recently, the very start of the solar system from the same reservoir Asphaug et al. (2011) enhanced its credibility with a of nebular dust as went to make the Sun (e.g., Wood computer simulation of how chondrules might form 1988). This view stems from the remarkable similarity from magma released as a result of collisions. between the chemical composition of chondrites and that A great deal more is known today about the early of the Sun’s photosphere for all elements other than a few solar system than was known 30 yr ago. The past that normally occur in gases (e.g., H, He, C, N, Ar). The 5–10 yr in particular have witnessed major view is reinforced by the presence in chondrites of CAIs, improvements in mass spectrometry and meteorite which are the oldest dated objects with a solar system chronology, significant developments in the modeling of isotopic signature (Amelin et al. 2002, 2010). Indeed, the planetesimal melting and of conditions in the solar time of CAI formation has now been widely adopted as nebula, and a substantial increase in the number and defining the start of the solar system (t=0). In addition, variety of meteorites available for study. The same chondrites contain pristine grains of stardust that are even recent period has also seen much exchange of ideas older than the solar system (e.g., Hoppe 2008). Thus, between meteorite researchers, astronomers, and conventional thinking holds that chondrules, along with planetary scientists. Observations of disks around CAIs, were created directly from clumps of nebular dust young stars, discoveries of extra-solar planetary at the outset, before the first planetesimals (presumed to systems, and computer simulations of orbital dynamics be the chondrite parent bodies) had accreted. It further have revolutionized our thinking on the formation of holds that after their accretion, some chondritic the asteroid belt. Together, these advances are bringing planetesimals became overheated, melted, and into focus a new picture of the young solar system that differentiated into molten metal cores and basaltic crusts, is significantly different from the one that has been the sources, respectively, of iron and basaltic meteorites conventionally portrayed. (e.g., Lauretta and McSween 2006). 2172 I. S. Sanders and E. R. D. Scott However, this intuitive and long-established dating (Kleine et al. 2008). As the chondrite parent interpretation of meteorites has recently been challenged asteroids were assembled
Load more

Recommended publications
  • Accretion of Water in Carbonaceous Chondrites: Current Evidence and Implications for the Delivery of Water to Early Earth
    ACCRETION OF WATER IN CARBONACEOUS CHONDRITES: CURRENT EVIDENCE AND IMPLICATIONS FOR THE DELIVERY OF WATER TO EARLY EARTH Josep M. Trigo-Rodríguez1,2, Albert Rimola3, Safoura Tanbakouei1,3, Victoria Cabedo Soto1,3, and Martin Lee4 1 Institute of Space Sciences (CSIC), Campus UAB, Facultat de Ciències, Torre C5-parell-2ª, 08193 Bellaterra, Barcelona, Catalonia, Spain. E-mail: [email protected] 2 Institut d’Estudis Espacials de Catalunya (IEEC), Edif.. Nexus, c/Gran Capità, 2-4, 08034 Barcelona, Catalonia, Spain 3 Departament de Química, Universitat Autònoma de Barcelona, 08193 Bellaterra, Catalonia, Spain. E-mail: [email protected] 4 School of Geographical and Earth Sciences, University of Glasgow, Gregory Building, Lilybank Gardens, Glasgow G12 8QQ, UK. Manuscript Pages: 37 Tables: 2 Figures: 10 Keywords: comet; asteroid; meteoroid; meteorite; minor bodies; primitive; tensile strength Accepted in Space Science Reviews (SPAC-D-18-00036R3, Vol. Ices in the Solar System) DOI: 10.1007/s11214-019-0583-0 Abstract: Protoplanetary disks are dust-rich structures around young stars. The crystalline and amorphous materials contained within these disks are variably thermally processed and accreted to make bodies of a wide range of sizes and compositions, depending on the heliocentric distance of formation. The chondritic meteorites are fragments of relatively small and undifferentiated bodies, and the minerals that they contain carry chemical signatures providing information about the early environment available for planetesimal formation. A current hot topic of debate is the delivery of volatiles to terrestrial planets, understanding that they were built from planetesimals formed under far more reducing conditions than the primordial carbonaceous chondritic bodies.
    [Show full text]
  • New Major and Trace Element Data from Acapulcoite-Lodranite Clan
    52nd Lunar and Planetary Science Conference 2021 (LPI Contrib. No. 2548) 1307.pdf New Major and Trace Element Data from Acapulcoite-Lodranite Clan Meteorites: Evidence for Melt-Rock Reaction Events and Early Collisional Fragmentation of the Parent Body Michael P. Lucas1, Nick Dygert1, Nathaniel R. Miller2, and Harry Y. McSween1, 1Department of Earth & Planetary Sciences, University of Tennessee, Knoxville, [email protected], 2Department of Geological Sciences, Univer- sity of Texas at Austin. Introduction: New major and trace element data illumi- patterns exhibit negative Eu anomalies. REE patterns are nate the magmatic and thermal evolution of the acapul- generally consistent among the three groups, however coite-lodranite parent body (ALPB). We observe major comparison of calculated equilibrium melts for acapulco- and trace element disequilibrium in the acapulcoite and ite and transitional cpx and opx demonstrates disequilib- transitional groups that provide evidence for melt infil- rium partitioning in those samples, especially for light- tration and melt-rock reaction processes. In lodranites, REEs in cpx. In contrast, lodranites are in apparent trace which represent sources of the infiltrating melts, we ob- element equilibrium (Fig 1b). They are depleted in serve rapid cooling from high temperatures (hereafter REE+Y relative to acapulcoite-transitional samples in temps), consistent with collisional fragmentation of the cpx (Fig. 1a), and display consistent REE abundances parent body during differentiation. except NWA 5488, which
    [Show full text]
  • Experimental and Petrological Constraints on Lunar Differentiation from the Apollo 15 Green Picritic Glasses
    Meteoritics & Planetary Science 38, Nr 4, 515–527(2003) Abstract available online at http://meteoritics.org Experimental and petrological constraints on lunar differentiation from the Apollo 15 green picritic glasses Linda T. ELKINS-TANTON,1* Nilanjan CHATTERJEE,2 and Timothy L. GROVE2 1Department of Geological Sciences, Brown University, Providence, Rhode Island, 02912, USA 2Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA *Corresponding author: [email protected] (Received 15 July 2002; revision accepted 23 September 2002) Abstract–Phase equilibrium experiments on the most magnesian Apollo 15C green picritic glass composition indicate a multiple saturation point with olivine and orthopyroxene at 1520°C and 1.3 GPa (about 260 km depth in the moon). This composition has the highest Mg# of any lunar picritic glass and the shallowest multiple saturation point. Experiments on an Apollo 15A composition indicate a multiple saturation point with olivine and orthopyroxene at 1520°C and 2.2 GPa (about 440 km depth in the moon). The importance of the distinctive compositional trends of the Apollo 15 groups A, B, and C picritic glasses merits the reanalysis of NASA slide 15426,72 with modern electron microprobe techniques. We confirm the compositional trends reported by Delano (1979, 1986) in the major element oxides SiO2, TiO2, Al2O3, Cr2O3, FeO, MnO, MgO, and CaO, and we also obtained data for the trace elements P2O5, K2O, Na2O, NiO, S, Cu, Cl, Zn, and F. Petrogenetic modeling demonstrates that the Apollo 15 A-B-C glass trends could not have been formed by fractional crystallization or any continuous assimilation/fractional crystallization (AFC) process.
    [Show full text]
  • Hf–W Thermochronometry: II. Accretion and Thermal History of the Acapulcoite–Lodranite Parent Body
    Earth and Planetary Science Letters 284 (2009) 168–178 Contents lists available at ScienceDirect Earth and Planetary Science Letters journal homepage: www.elsevier.com/locate/epsl Hf–W thermochronometry: II. Accretion and thermal history of the acapulcoite–lodranite parent body Mathieu Touboul a,⁎, Thorsten Kleine a, Bernard Bourdon a, James A. Van Orman b, Colin Maden a, Jutta Zipfel c a Institute of Isotope Geochemistry and Mineral Resources, ETH Zurich, Clausiusstrasse 25, 8092 Zurich, Switzerland b Department of Geological Sciences, Case Western Reserve University, Cleveland, OH, USA c Forschungsinstitut und Naturmuseum Senckenberg, Frankfurt am Main, Germany article info abstract Article history: Acapulcoites and lodranites are highly metamorphosed to partially molten meteorites with mineral and bulk Received 11 November 2008 compositions similar to those of ordinary chondrites. These properties place the acapulcoites and lodranites Received in revised form 8 April 2009 between the unmelted chondrites and the differentiated meteorites and as such acapulcoites–lodranites are Accepted 9 April 2009 of special interest for understanding the initial stages of asteroid differentiation as well as the role of 26Al Available online 3 June 2009 heating in the thermal history of asteroids. To constrain the accretion timescale and thermal history of the Editor: R.W. Carlson acapulcoite–lodranite parent body, and to compare these results to the thermal histories of other meteorite parent bodies, the Hf–W system was applied to several acapulcoites and lodranites. Acapulcoites Dhofar 125 Keywords: – Δ chronology and NWA 2775 and lodranite NWA 2627 have indistinguishable Hf W ages of tCAI =5.2±0.9 Ma and Δ isochron tCAI =5.7±1.0 Ma, corresponding to absolute ages of 4563.1±0.8 Ma and 4562.6±0.9 Ma.
    [Show full text]
  • Presolar Grains As Tracers of Nebular and Parent Body Process- Ing of Chondritic Material
    Workshop on Parent-Body and Nebular Modification of Chondritic Materials 4019.pdf PRESOLAR GRAINS AS TRACERS OF NEBULAR AND PARENT BODY PROCESS- ING OF CHONDRITIC MATERIAL. Gary R. Huss, Lunatic Asylum of the Charles Arms Laboratory, Division of Geological and Planetary Sciences, 170-25, California Institute of Tech- nology, Pasadena, CA 91125 Presolar grains such as diamond, SiC, These observations show that a single wide- graphite, and Al2O3 are present in the least al- spread reservoir of presolar grains was sam- tered members of all chondrite classes [1,2]. pled by all chondrite classes. This reservoir is These grains reside in the fine-grained “matrix” most plausibly the dust from the solar system’s and did not experience the chondrule-forming parent molecular cloud. process. Because most types of presolar grains The CI chondrite, Orgueil, and the matrices are chemically unstable in putative nebular of CM2 chondrites have the highest matrix- conditions and in chondritic meteorites, they normalized abundances of silicon carbide, and serve as sensitive monitors of nebular and par- graphite; have among the highest diamond ent-body conditions. abundances; and have diamonds with high ni- Tracers of Metamorphism: Isotopic and trogen contents and the highest contents of P3 trace element characteristics of some presolar noble gases [1-4]. These characteristics indi- material and the abundances of presolar grains cate that CI chondrites and the matrices of in “matrix” are functions of the metamorphic CM2 chondrites contain the least processed history of the host meteorite [1–4]. Currently sample of the presolar-grains reservoir from recognized presolar grains show a range of the sun’s parent molecular cloud.
    [Show full text]
  • Asteroids 2867 Steins and 21 Lutetia: Surface Composition from Far Infrared Observations with the Spitzer Space Telescope
    A&A 477, 665–670 (2008) Astronomy DOI: 10.1051/0004-6361:20078085 & c ESO 2007 Astrophysics Asteroids 2867 Steins and 21 Lutetia: surface composition from far infrared observations with the Spitzer space telescope M. A. Barucci1, S. Fornasier1,2,E.Dotto3,P.L.Lamy4, L. Jorda4, O. Groussin4,J.R.Brucato5, J. Carvano6, A. Alvarez-Candal1, D. Cruikshank7, and M. Fulchignoni1,2 1 LESIA, Observatoire de Paris, 92195 Meudon Principal Cedex, France e-mail: [email protected] 2 Université Paris Diderot, Paris VII, France 3 INAF, Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Roma, Italy 4 Laboratoire d’Astrophysique de Marseille, BP 8, 13376 Marseille Cedex 12, France 5 INAF, Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy 6 Observatorio National (COAA), rua Gal. José Cristino 77, CEP20921–400 Rio de Janeiro, Brazil 7 NASA Ames Research Center, MS 245-6, Moffett Field, CA 94035-1000, USA Received 14 June 2007 / Accepted 3 October 2007 ABSTRACT Aims. The aim of this paper is to investigate the surface composition of the two asteroids 21 Lutetia and 2867 Steins, targets of the Rosetta space mission. Methods. We observed the two asteroids through their full rotational periods with the Infrared Spectrograph of the Spitzer Space Telescope to investigate the surface properties. The analysis of their thermal emission spectra was carried out to detect emissivity features that diagnose the surface composition. Results. For both asteroids, the Christiansen peak, the Reststrahlen, and the Transparency features were detected. The thermal emissiv- ity shows a clear analogy to carbonaceous chondrite meteorites, in particular to the CO–CV types for 21 Lutetia, while for 2867 Steins, already suggested as belonging to the E-type asteroids, the similarity to the enstatite achondrite meteorite is confirmed.
    [Show full text]
  • Chondrites and Chondrules Analogous to Sediments Dr
    Chondrites and Chondrules Analogous to Sediments Dr. Richard K. Herd Curator, National Meteorite Collection, Geological Survey of Canada, Natural Resources Canada (Retired) 51st Annual Lunar and Planetary Science Conference Houston, Texas March 16-20, 2020 Introduction and Summary • Comparing chondrites and terrestrial conglomerates [1] continues • Meteorites are fragmental rocks, continually subjected to impacts and collisions, whatever their ultimate origin in space and time • Space outside Earth’s atmosphere may be considered a 4D debris field • Of the debris that reaches the surface of Earth and is available for study, > 80 % are chondrites • Chondrites and chondrules are generally considered the product of heating of dust in the early Solar System, and therefore effectively igneous in origin • Modelling these abundant and important space rocks as analogous to terrestrial detrital sediments, specifically conglomerates, is innovative, can help derive data on their true origins and history, and provide con text for ongoing analyses Chondrites and Chondrules • Chondrites are rocks made of rocks • They are composed of chondrules and chondrule-like objects from which they take their name • Chondrules are roughly spheroidal pebble-like rocks predominantly composed of olivine, pyroxene, feldspar, iron-nickel minerals, chromite, magnetite, sulphides etc. • They range from nanoscale to more than a centimetre, with some size variation by chondrite type. There are thousands/millions of them available for study • Hundreds of chondrules fill the area of a single 3.5 x 2.5 cm standard thin section What is Known ? • Adjacent chondrules may be millions of years different in age • They date from the time of earliest solar system objects (viz.
    [Show full text]
  • Metal-Silicate Fractionation and Chondrule Formation
    A756 Goldschmidt 2004, Copenhagen 6.3.12 6.3.13 Metal-silicate fractionation and Fe isotopes fractionation in chondrule formation: Fe isotope experimental chondrules 1 2 2,3 constraints S. LEVASSEUR , B. A. COHEN , B. ZANDA , 2 1 1 1 1 2 2 R.H. HEWINS AND A.N. HALLIDAY X.K. ZHU , Y. GUO , S.H. TANG , A. GALY , R.D. ASH 2 AND R.K O’NIONS 1 ETHZ, Dep. of Earth Sciences, Zürich, Switzerland ([email protected]) 1 Lab of Isotope Geology, MLR, Chinese Academy of 2 Rutgers University, Piscataway, NJ, USA Geological Sciences, 26Baiwanzhuang Road, Beijing, 3 Muséum National d’Histoire Naturelle, Paris, France China ([email protected]) 2 Department of Earth Sciences, Oxford University, Parks Road, Oxford, OX1 3PR, UK Natural chondrules show an Fe-isotopic mass fractionation range of a few δ-units [1,2] that is interpreted either as the result of Fe depletion from metal-silicate Recent studies have shown that considerable variations of fractionation during chondrule formation [1] or as the Fe isotopes exist in both meteoritic and terrestrial materials, reflection of the fractionation range of chondrule precursors and that they are related, through mass-dependent [2]. In order to better understand the iron isotopic fractionation, to a single isotopically homogeneous source[1]. compositions of chondrules we conducted experiments to This implies that the Fe isotope variations recorded in the study the effects of reduction and evaporation of iron on iron solar system materials must have resulted from mass isotope systematics. fractionation incurred by the processes within the solar system About 80mg of powdered slag fayalite was placed in a itself.
    [Show full text]
  • To Here from Eternity: the Story of the Bovedy, Crumlin and Leighlinbridge Meteorites
    TO HERE FROM ETERNITY The story of the Bovedy, Crumlin and Leighlinbridge meteorites Mike Simms, Ulster Museum Friday 25th April 1969 9.25 p.m. A fireball streaks across the night sky Friday 25th April 1969 9.25 p.m. A fireball streaks across the night sky It takes less than a minute to cross the UK! …and barely 15 seconds to cross Northern Ireland A small rock smashes a roof near Lisburn A bigger one lands in a field near Garvagh. These are meteorites - the first found in Ireland since 1902, and the last for another 30 years. Where else have they fallen in Ireland? Only 8 meteorite falls in 230 years! The Bovedy, Crumlin and Leighlinbridge meteorites all fell in the 20th Century Bovedy meteorite all are L3 Ordinary Chondrite Type L Ordinary Chondrites Crumlin meteorite (these are slices) L5 Ordinary Chondrite Leighlinbridge meteorite L6 Ordinary Chondrite Types of meteorites and their abundance (%) Stony Meteorites Falls Finds Ordinary Chondrites 76.9% 50.9% Carbonaceous Chondrites 3.7% Other chondrite types 1.7% Achondrites 7.7% Ungrouped 4.3% Irons 4.2% 20.8% Stony-irons 1.3% …which is why they are called Ordinary Chondrites. Types of Ordinary Chondrite (each comes from its own parent planet) Type H (High in iron) Mooresfort 1810 Limerick 1813 Killeter 1844 Dundrum 1865 Crumlin 1902 Bovedy 1969 Leighlinbridge 1999 Type L (Low in iron) In the beginning, >4568 million years ago… Star formation triggered by a supernova Al26 Fe60 The Sun forms. Planets accrete and melt. Planetismal accretion Melting (due to Al26 and Fe60) Differentiation Pallasite meteorites (planet mantle) Iron meteorites (planet core) Achondrite meteorites (planet crust) Pallasite meteorites (planet mantle) But none of these are chondrite meteorites… Iron meteorites (planet core) Achondrite meteorites (planet crust) How and when did the chondrules form? Sprucefield slice Splashes from the collision of molten planetismals.
    [Show full text]
  • Australian Aborigines and Meteorites
    Records of the Western Australian Museum 18: 93-101 (1996). Australian Aborigines and meteorites A.W.R. Bevan! and P. Bindon2 1Department of Earth and Planetary Sciences, 2 Department of Anthropology, Western Australian Museum, Francis Street, Perth, Western Australia 6000 Abstract - Numerous mythological references to meteoritic events by Aboriginal people in Australia contrast with the scant physical evidence of their interaction with meteoritic materials. Possible reasons for this are the unsuitability of some meteorites for tool making and the apparent inability of early Aborigines to work metallic materials. However, there is a strong possibility that Aborigines witnessed one or more of the several recent « 5000 yrs BP) meteorite impact events in Australia. Evidence for Aboriginal use of meteorites and the recognition of meteoritic events is critically evaluated. INTRODUCTION Australia, although for climatic and physiographic The ceremonial and practical significance of reasons they are rarely found in tropical Australia. Australian tektites (australites) in Aboriginal life is The history of the recovery of meteorites in extensively documented (Baker 1957 and Australia has been reviewed by Bevan (1992). references therein; Edwards 1966). However, Within the continent there are two significant areas despite abundant evidence throughout the world for the recovery of meteorites: the Nullarbor that many other ancient civilizations recognised, Region, and the area around the Menindee Lakes utilized and even revered meteorites (particularly of western New South Wales. These accumulations meteoritic iron) (e.g., see Buchwald 1975 and have resulted from prolonged aridity that has references therein), there is very little physical or allowed the preservation of meteorites for documentary evidence of Aboriginal acknowledge­ thousands of years after their fall, and the large ment or use of meteoritic materials.
    [Show full text]
  • Magnetite Biomineralization and Ancient Life on Mars Richard B Frankel* and Peter R Buseckt
    Magnetite biomineralization and ancient life on Mars Richard B Frankel* and Peter R Buseckt Certain chemical and mineral features of the Martian meteorite with a mass distribution unlike terrestrial PAHs or those from ALH84001 were reported in 1996 to be probable evidence of other meteorites; thirdly, bacterium-shaped objects (BSOs) ancient life on Mars. In spite of new observations and up to several hundred nanometers long that resemble fos­ interpretations, the question of ancient life on Mars remains silized terrestrial microorganisms; and lastly, 10-100 nm unresolved. Putative biogenic, nanometer magnetite has now magnetite (Fe304), pyrrhotite (Fel_xS), and greigite (Fe3S4) become a leading focus in the debate. crystals. These minerals were cited as evidence because of their similarity to biogenic magnetic minerals in terrestrial Addresses magnetotactic bacteria. *Department of Physics, California Polytechnic State University, San Luis Obispo, California 93407, USA; e-mail: [email protected] The ancient life on Mars hypothesis has been extensively tDepartments of Geology and Chemistry/Biochemistry, Arizona State challenged, and alternative non-biological processes have University, Tempe, Arizona 85287-1404, USA; e-mail: [email protected] been proposed for each of the four features cited by McKay et al. [4]. In this paper we review the current situa­ tion regarding their proposed evidence, focusing on the Abbreviations putative biogenic magnetite crystals. BCM biologically controlled mineralization BIM biologically induced mineralization BSO bacterium-shaped object Evidence for and against ancient Martian life PAH polycyclic aromatic hydrocarbon PAHs and BSOs Reports of contamination by terrestrial organic materials [5°,6°] and the similarity of ALH84001 PAHs to non-bio­ genic PAHs in carbonaceous chondrites [7,8] make it Introduction difficult to positively identify PAHs of non-terrestrial, bio­ A 2 kg carbonaceous stony meteorite, designated genic origin.
    [Show full text]
  • Brecciation and Chemical Heterogeneities of CI Chondrites
    Geochimica et Cosmochimica Acta 70 (2006) 5371–5394 www.elsevier.com/locate/gca Brecciation and chemical heterogeneities of CI chondrites Andreas Morlok a,b,*, Addi Bischoff a, Thomas Stephan a, Christine Floss c, Ernst Zinner c, Elmar K. Jessberger a a Institut fu¨r Planetologie, Wilhelm-Klemm-Strasse 10, 48149 Mu¨nster, Germany b Department of Earth and Planetary Sciences, Faculty of Science, Kobe University, Kobe 657-8501, Japan c Laboratory for Space Sciences and Physics Department, Washington University, St. Louis, MO, USA Received 5 December 2005; accepted in revised form 3 August 2006 Abstract Fragments in the size range from 40 lm to several hundred lm in the CI chondrites Orgueil, Ivuna, Alais, and Tonk show a wide range of chemical compositions with variations in major elements such as iron (10.4–42.4 wt% FeO), silicon (12.7–42.2 wt% SiO2), and sulfur (1.01–15.8 wt% SO3), but also important minor elements such as phosphorous (up to 5.2 wt% P2O5) or calcium (up to 6.6 wt% CaO). These variations are the result of the varying mineralogical compositions of these fragments. The distribution of phyl- losilicates, magnetites, and possibly ferrihydrite, in particular, control the abundances of these elements. High REE contents—up to 150 times the solar abundances—were observed in phosphates, while matrix and sulfates are REE-depleted. The studied 113 fragments were subdivided into eight lithologies with similar mineralogical and thus chemical properties. The most common is the CGA lithology, consisting of a groundmass of Mg-rich, coarse-grained phyllosilicates and varying abundances of inclusions such as magnetite.
    [Show full text]