McSween et al.: Recent Advances in and 53

Recent Advances in Meteoritics and Cosmochemistry

Harry Y. McSween Jr. University of Tennessee

Dante S. Lauretta University of Arizona

Laurie A. Leshin Arizona State University

Major advances in research on extraterrestrial (, , inter- planetary dust , and ) since the first edition of Meteorites and the Early are highlighted. Topics include the importance of newly recognized groups; new discoveries about the presolar and nebular components of and inter- planetary dust particles; improvements in early solar system chronology using short-lived radio- ; new insights into cosmochemical abundances, fractionations, and nebular reservoirs; and advances in reading nebular and prenebular records through a haze of secondary processes. Some significant new insights based on these data are that the early solar system experienced a bewildering variety of nucleosynthetic inputs, the was a dynamic entity with transient heating events, and the system of and planets evolved more rapidly than previously appreciated.

1. INTRODUCTION omit martian and lunar meteorites from consideration, ex- cept where they bear on the timing of planet and The goal of the first edition of Meteorites and the Early early differentiation. Solar System (Kerridge and Matthews, 1988) was to inter- pret the meteoritic record in terms of constraints on theo- 2. EXTRATERRESTRIAL MATERIALS ries of the origin and early of the solar system. AVAILABLE FOR STUDY That is also the intent of this volume. Here we briefly high- significant new discoveries in meteoritics and cosmo- 2.1. Newly Recognized Groups since the publication of the first edition. The following chapters will explain in more detail how these attempts to document differences breakthroughs have constrained our understanding of pro- and linkages among meteorites — a critical first step be- cesses and events prior to and within the early solar sys- cause variations and trends among members of a group can tem. The breakthroughs introduced here are assigned to ep- reveal the processes that produced them. In the first edition, ochs, following the general organization of the book. 9 groups of chondrites, 4 groups of , 2 stony- We acknowledge that our choices of critical advances in iron groups, and 13 groups were recognized. meteoritics and cosmochemistry are subjective but, we be- Other anomalous meteorites (distinct individual specimens lieve, defensible. In citing literature, we have focused on or groups having less than five members) were also known. original discovery papers or, in some cases, comprehensive Since that time, new meteorites found in Antarctica and hot reviews. To make this task tractable, we consider research deserts have considerably expanded our collections, and a on meteoritic samples per se and do not review the consid- recent compilation of meteorites (including ungrouped sam- erable progress made in providing geologic context through ples, clasts in , and micrometeorites) suggested that the identification and study of their or cometary perhaps ~135 asteroidal parent bodies may be represented parent bodies. A comprehensive treatment of advances in (Meibom and Clark, 1999). asteroid , spacecraft encounters with , Several new classes of chondrites — one distinct - and mechanisms for the delivery of meteorites from aster- drite group (the Rumuruti or R group) and four carbona- oids to can be found in a recently published compan- ceous chondrite groups (CR, CH, CB, CK) — have been volume, Asteroids III (Bottke et al., 2002). Likewise, the defined. The R chondrites (Bischoff et al., 1993; Rubin context and insights provided by new astrophysical theory and Kallemeyn, 1994; Schulze et al., 1994; Kallemeyn et and astronomical observations are not catalogued here, but al., 1996) are the most highly oxidized anhydrous chon- will be considered in other chapters. Given that the present drite group, containing no and high fayalite volume is not concerned with later planetary evolution, we contents, with fewer than ordinary chondrites

53 54 Meteorites and the Early Solar System II

experienced such low degrees of that they retain relict chondritic textures. However, we favor applying the classification to all residues from partial melting, regard- less of the degree of melting. Iron/magnesium/manganese provide an effective means of distinguishing primitive achondrites and (igneous) achondrites (Goodrich and Delaney, 2000). Newly classified groups of primitive achondrites include the - (Fig. 2) (Mc- Coy et al., 1996, 1997), (Nehru et al., 1992), and (Benedix et al., 1998). , although not a newly defined group, are now also recognized as primitive achondrites, and the complementary basaltic component for Fig. 1. Photomicrograph of the 013 Rumaruti chon- these residues occurs as plagioclase-bearing clasts (Kita et drite (width of section = 36 mm), showing the brecciated texture that is common in these meteorites. Large clasts at the upper cen- al., 2004). ter and right are impact melts, whereas other clasts are unmelted Among the achondrites, (Mittlefehldt and Lind- but show different degrees of thermal . Courtesy strom, 1990) constitute a newly defined group due to the of A. Bischoff, University of Münster. addition of new meteorites. These basaltic meteorites are dominated by high abundances of refractory elements and low oxidation state. A few lunar and martian meteorites (all (Fig. 1). The CR (Weisberg et al., 1993), CH (Grossman achondrites) were recognized prior to publication of the first et al., 1988; Scott, 1988), and CB (Weisberg et al., 2001) edition, but not discussed in that volume; the numbers of groups are among the most primitive types of chondrites these meteorites have markedly increased. The discovery that (Krot et al., 2002a). These chondrites have large amounts the NWA 011 basaltic (Fig. 3) has distinct Fe/Mn of metal, but are classified as carbonaceous based on chem- and O from otherwise similar (Yamaguchi istry and O isotopes. The CK group (Kallemeyn et al., 1991) et al., 2002) demonstrates that multiple differentiated aster- contains the most highly metamorphosed carbonaceous oids yielded basaltic meteorites. chondrites. However, Greenwood et al. (2003) have ques- tioned whether CK and equilibrated CV chondrites are re- 3. THE PRESOLAR EPOCH ally distinct groups, and Rubin et al. (2003) suggested that the CB chondrite designation may be misleading because 3.1. Presolar Grains that group may have formed by nonnebular processes. Several remarkable chondrites that have proved difficult The study of minute grains found in the fine- to classify have been described as well. The newly recov- grained () portions of chondrites has burgeoned since ered meteorite (Brown et al., 2000), a carbona- the first edition, owing to the isolation of these grains in ceous chondrite of uncertain affinity, contains volatile-ele- the laboratory and their analysis using the ion microprobe. ment abundances straddling those of CI and CM chondrites The phases most intensely studied are , silicon (Mittlefehldt, 2002), along with chondrules and inclusions carbide, , , , , and similar to those in CM chondrites (Simon and Grossman, (Anders and Zinner, 1993; Ott, 1993; Bernatowicz 2003). However, Tagish Lake experienced a more perva- sive alteration history than CMs. Anomalous ordinary chon- drites of very low metamorphic grade and containing large quantities of refractory inclusions have also been described (Kimura et al., 2002).

2.2. Newly Recognized Achondrite Groups

Primitive achondrites, which were not distinguished from achondrites (crystallized melts) in the first edition, are now generally recognized to be residues from partial melting (Goodrich and Delaney, 2000). The major-element compo- sitions of most primitive achondrites are approximately chondritic, but elements residing in with low melt- ing points and incompatible trace elements that are concen- trated in partial melts have been depleted in them. Some Fig. 2. Photomicrograph of Acapulco, a primitive achondrites have experienced higher degrees of () (width of section = 4.7 mm), showing its thoroughly melting, so that they no longer retain chondritic major-ele- recrystallized texture. Courtesy of T. McCoy, Smithsonian Insti- ment compositions, and other primitive achondrites have tution. McSween et al.: Recent Advances in Meteoritics and Cosmochemistry 55

The exotic of presolar grains is demonstrated by their isotopic compositions, the diversity of which points toward formation in multiple stellar environments. For ex- ample, the carriers of the 22Ne-rich components Ne-E(L) and Ne-E(H) (released at low and high respec- tively), which provided the first hint that chondrites con- tained interstellar materials, have now been identified as graphite (Amari et al., 1990) and SiC (Lewis et al., 1990), respectively. The morphologies and microstructures of pre- solar grains also reveal information on the conditions of dust formation in stellar regions (Bernatowicz et al., 1996, 2003). Lack of sputtering effects and the possibility of organic coatings suggest mantles of may have protected SiC grains in the (Bernatowicz et al., 2003). Presolar grains occur in the matrices of all chondrite Fig. 3. Photomicrograph of Northwest Africa 011, a unique ba- groups in varying proportions (Huss and Lewis, 1995). saltic achondrite consisting mostly of large pigeonite grains in a Isotopic analyses of interstellar grains have provided groundmass of pigeonite and plagioclase (plain polarized light, rigorous tests of models for and evolution width of field = 5.2 mm). Courtesy of A. Yamaguchi, National in red giants, (AGB) , super- Institute of Polar Research. novae, and novae (Bernatowicz and Zinner, 1997; Zinner, 1998; Nittler, 2003). These data provide stunning confirma- tions of predictions of the products of s-process nucleosyn- and Zinner, 1997; Zinner, 1998; Hoppe and Zinner, 2000; thesis, although no pure r-process pattern has yet been Nittler, 2003). Titanium carbide and FeNi metal occur as found in presolar grains. These grains also provide informa- minute inclusions within presolar graphite grains (Fig. 4). tion on galactic chemical evolution. For example, isotopes All these phases are refractory, and the -bearing of Si and Ti in do not conform to predictions phases formed under reducing conditions. Presolar silicates for and are thought to reflect ranges have also now been recognized in both interplanetary dust of initial composition of parent stars (Alexander and Nittler, particles (Messenger et al., 2003) and chondrites (Nguyen 1999). and Zinner, 2004). 3.2. Interplanetary Dust Particles

Tiny interplanetary dust particles (IDPs), collected in the stratosphere by aircraft, were described in the first edition. Advances in microanalytical technology have allowed im- proved characterization of these very small meteoritic ma- terials (Rietmeijer, 1998). Interplanetary dust particles sam- ple, at least in part, parent bodies distinct from those of macrometeorites. The first edition focused on the , textures, and optical properties (from transmission spectra) of IDPs. More recent research indicates that most IDPs are more primitive than CI chondrites. Bradley et al. (1996) obtained the first reflectance spectra of anhydrous IDPs, for which there are no meteorite counterparts. They suggested that these IDPs are samples of primitive P or D asteroids in the outer main belt. Some anhydrous IDPs are probably from (Brownlee et al., 1995). Detailed studies reveal that anhydrous IDPs contain abundant (organic) and silicate stardust (Messenger, 2000; Messenger et al., 2003). with embedded metal and sulfide (GEMS) (Fig. 5) are an- Fig. 4. Ultrathin section of presolar graphite, containing a 70- nm-long of TiC that served as a nucleation center for con- other interesting component of IDPs (Bradley, 1994). These densation of graphite in the outflowing around an AGB . grains have appreciable histories, as expected if The graphite structure is concentric layers, and the radial spokes they once resided in the interstellar medium, so they may are an effect. Courtesy of T. J. Bernatowicz, be the irradiated remnants of cosmically abundant presolar Washington University. silicate grains. However, very few GEMS have anomalous 56 Meteorites and the Early Solar System II

A significant discovery concerning organic compounds is the determination that nonbiogenic amino are pres- ent as nonracemic mixtures in carbonaceous chondrites. Small but measurable excesses of the L-enantiomers of amino acids have been demonstrated to have a nonbiologic (Cronin and Pizzarello, 1997) and nonterrestrial (Engel and Macko, 1997) origin. How slightly optically active organic compounds would be produced in the interstellar medium is not understood, but selective destruction of one enanti- omer by UV circularly polarized light from stars in a presolar cloud has been invoked. Hydrocarbons with large H- and N-isotopic anomalies in anhydrous IDPs likely formed in molecular clouds (Keller et al., 2004), although organic occurs in comparable abundance in hydrated IDPs (Flynn et al., 2003).

4. THE DISK FORMATION EPOCH Fig. 5. Brightfield transmission electron micrograph of glass with embedded metal and sulfides (GEMS) within a thin section of 4.1. Presolar Grain Survival and Chronology an interplanetary dust . GEMS are composed of rounded, nanometer-sized and pyrrhotite in Mg-rich sili- cate glass. The properties of GEMS appear to have been shaped by Because of destructive oxidation reactions, the lifetimes chronic exposure to , and they resemble amor- of presolar SiC grains exposed to a hot nebula are short phous silicates in the interstellar medium. Courtesy of J. Bradley, compared to nebula cooling timescales (Mendybaev et al., Lawrence Livermore National Laboratory. 2002). Attempts to date presolar silicon carbide grains based on the production of spallogenic 21Ne give surprisingly low ages of ~10–130 Ma (Tang and Anders, 1988). However, recoil suggest that micrometer-sized SiC grains O isotopic compositions (Messenger et al., 2003) of the will have lost virtually all Ne produced in the interstellar magnitude of other presolar oxides (Nittler et al., 1997). medium (Ott and Begemann, 2000), casting doubt on these ages. 3.3. Organic Compounds 4.2. Nebular Elemental and Isotopic Abundances The structure and stable isotopic composition of organic compounds in chondrites reflect complex interstellar, nebu- Anders and Grevesse (1989), Lodders (2003), and Palme lar, and planetary processes whose resolution may be con- and Jones (2003) compiled new average solar system ele- founded by terrestrial (Gilmour, 2003). The mental and isotopic abundances for CI chondrites. These first edition focused on abiotic synthesis mechanisms in- were compared with solar photosphere compositions, which ferred for the most extensively studied organic compounds have also been updated (Palme and Jones, 2003, and refer- in CM carbonaceous chondrites. ences therein). The solar O abundance has been revised down- Compound-specific stable- measurement on me- ward by 50% and the C abundance by a smaller amount teoritic organic matter is a significant new development. The (Allende Prieto et al., 2001), leading to a higher C/O ratio D/H enrichment of bulk organic matter, described in the first and thus somewhat more reducing nebular gas than envi- edition, has now been measured in amino and sulfonic acids sioned in the first edition (Allende Prieto et al., 2002). There (Cooper et al., 1997) and suggests synthesis by ion-- have also been significant downward revisions in S, Se, and cule reactions in the interstellar medium. Enrichment of 33S P, and new solar abundances of light elements support the in sulfonic is attributed to UV irradiation in an inter- previous conclusion that Li is depleted in the . stellar environment (Cooper et al., 1997). Values of δ13C The smoothness of heavy-element abundance patterns in low-molecular-weight compounds become more positive was formerly used to support the choice of CI chondrites as the amount of C in the increases, whereas the in determining solar system abundances; however, some opposite trend is observed in high-molecular-weight com- measured discontinuities are real (Burnett et al., 1989) so pounds (Sephton et al., 1999, 2000). These are kinetic sig- this reasoning is flawed. The recognition that sulfate veins of both bond formation (synthesis from simpler in probably formed during the meteorite’s residence compounds) and bond destruction ( of higher ho- on Earth (Gounelle and Zolensky, 2001) suggests open-sys- mologs to form lower ones). Such trends may suggest that tem modification of soluble components like S. The Tagish the carbon skeletons formed within icy mantles on inter- Lake meteorite has been suggested to be a better proxy for stellar grains, where radiation-induced reactions create and solar system abundances than CI chondrites (Brown et al., destroy organic matter. 2000; Zolensky et al., 2002). McSween et al.: Recent Advances in Meteoritics and Cosmochemistry 57

4.3. Isotopic Reservoirs ply to other nebular materials, perhaps explaining an appar- ent age difference of several million years (based on 26Al) The slope of the O-isotope mixing line for bulk refractory between CAIs and chondrules. However, this age difference inclusions (calcium-aluminum-rich inclusions, or CAIs) is is supported by 53Mn and 129I data (Swindle et al., 1996) ~0.95, but new microanalyses of inclusions suggest a slope and very precise Pb-Pb ages (Amelin et al., 2002) for CAIs of 1.00 (Young and Russell, 1998). The distinction is impor- and chondrules. tant for distinguishing between competing mechanisms for As noted in the first edition, short-lived radionuclide production of a 16O-rich reservoir. One interpretation is that chronometers commonly show inconsistent timescales, a this reservoir represents a nucleosynthetic enrichment in the problem that has not yet been fully resolved. However, 129I- nebula, possibly inherited from a nearby . An al- 129Xe dates for unshocked meteorites can now be reconciled ternative hypothesis is -independent fractionation of with 26Al and 53Mn chronologies (Gilmour et al., 2000). 16O (Thiemens, 1996), perhaps through self-shielding of CO The age of the solar system is now based on a combina- in the nebula (Clayton, 2002). A 0.95 slope would rule out tion of long- and short-lived chronometers applied to refrac- the possibility of mass-independent chemical fractionation of tory inclusions in chondrites. 235U/238U-207Pb/206Pb ages of O isotopes in the nebula, but either mechanism is permitted 4566 Ma for Allende CAIs (Allègre et al., 1995) and 4567 Ma by a 1.00 slope (Ireland and Fegley, 2000). Analyses of O for Efremovka CAIs (Amelin et al., 2002) may be a lower isotopes in condensate in amoeboid olivine aggre- age limit if the inclusions were altered. This age is slightly gates (AOAs) suggest a 16O-rich nebular gas (Krot et al., older than the 4559-Ma estimate in the first edition. Lug- 2002b), whereas chondrules generally formed in equilibrium mair and Shukolyukov (2001) defined lower (4568 Ma) and with a more 16O-poor gas. The 16O-rich gas may have re- upper (4571 Ma) age limits, based on constraints from sulted from mass-independent fractionation or 53Mn-53Cr, in agreement with the upper limit for the CAI of dust-enhanced regions. 207Pb-206Pb age and with 26Al and 129I data for the Ste. Marguerite. 5. THE FIRST NEBULAR EPOCH Unambiguous evidence of three especially important extinct radionuclides has been discovered since the first 5.1. Nebular Chronology and Origin of edition. Two of these bear directly on the question of the Short-lived Radioisotopes sources of short-lived nuclides, with apparently contradic- tory implications. The finding of live 10Be in CAIs (McKee- The first edition included seven chapters on chronology, gan et al., 2000) is important because this is not reflecting the importance of understanding the temporal produced via nucleosythesis in stars and thus is generally sequence and duration of early solar system events and interpreted to be evidence for local production of at least processes. The most significant new advance in meteorite some short-lived isotopes by spallation reactions in the neb- geochronology is the development of new high-resolution ula. However, 10Be and 26Al are decoupled in many CAIs chronometers based on short-lived radionuclides. The six (Marhas et al., 2002), suggesting that 26Al was not a prod- extinct radionuclides discussed in the first edition have now uct of spallation. Evidence in meteorites for live 60Fe (Shu- been augmented by meteorite dating techniques based on kolyukov and Lugmair, 1993; Tachibana and Huss, 2003), 10Be-10B, 41Ca-41K, 60Fe-60Ni, 146Sm-142Nd, 182Hf-182W, which is only formed through stellar nucleosynthesis, also 92Nb-92Zr, 187Re-187Os, and 107Pd-107Ag (McKeegan and contradicts the idea that all short-lived radioactivities were Davis, 2004). A major challenge in using these isotopic sys- locally produced. These nuclides were probably produced tems is in understanding how they were produced, which in stars and imported within presolar grains (MacPherson bears on what events are actually dated. et al., 2003). Finally, with a half- of 103 Ka, 41Ca is the Significant advances have been made in the 53Mn-53Cr shortest-lived isotope yet confirmed to be present in chon- (Lugmair and Shukolyukov, 2001) system, which appears to drites (Srinivasan et al., 1994). This age constrains the time- be a useful chronometer despite evidence that 53Mn was not scale from synthesis to injection of short-lived isotopes to distributed homogeneously in the nebula. This chronometer be very short. dates fractionation of Mn from Cr, due primarily to Mn vol- atility (Palme, 2001). However, 53Mn data have found a 5.2. Nebular Condensates and Residues variety of applications, such as constraining the timing of aqueous alteration to form carbonates in carbonaceous chon- The requirement for a hot nebula to allow vaporization drites to <20 m.y. after accretion (Endress et al., 1996). and condensation, a popular idea in the first edition, has now Considerable attention has also been focused on 26Al- been circumvented by models in which heating of the disk 26Mg. The idea that 26Al was homogenously distributed in occurs close to the protosun and the materials are redistrib- the neb-ula (MacPherson et al., 1995) has been challenged uted outward (the X- model). Shu et al. (1996) de- by argu-ments that it was produced by local irradiation in scribed a scenario in which various chondrite components an X-wind region of the early Sun (Gounelle et al., 2001). might have been formed far from the positions of their ac- If refractory condensates incorporated this nuclide and were cretion into chondrites. The existence of 10Be in CAIs (Mc- then dispersed, the canonical 26Al/27Al ratio would not ap- Keegan et al., 2000), not formed during stellar nucleosyn- 58 Meteorites and the Early Solar System II

5.3. Nebular Chemical Fractionations

Cosmochemical behavior is dominated by element vola- tility, presumably reflecting either incomplete condensation or evaporation. The refractory elements are always assumed to be present in chondritic (CI) relative proportions; how- ever, two cases have now been shown to violate this as- sumption. Refractory Re/Os ratios in carbonaceous chon- drites are systematically lower than those in ordinary and enstatite chondrites (Walker et al., 2002), and Nb/Ta ratios in chondrites are variable (Weyer et al., 2003). Moderately volatile elements are depleted in achondrite parent bodies and in planets, relative to chondrites. How- ever, measured 41K/39K ratios among the terrestrial planets, the Moon, achondrites, and chondrites are uniform to within Fig. 6. Backscattered electron image of a CAI in the Adelaide ~2‰ (Humayun and Clayton, 1995). This lack of K-iso- . Corundum (cor) is replaced by hibonite tope fractionation has been argued to preclude evaporation (hib), which is in turn corroded by (grs). The inferred as an explanation for the observed volatile depletions. How- sequence is consistent with the equilibrium conden- ever, evaporation of nebular crystalline dust prior to its ac- sation at a total pressure ≤10–5 bar and ~1000 CI dust/gas enrich- cretion into planetesimals is possible (Young, 2000). ment relative to solar composition. Courtesy of A. Krot, University of Hawai‘i. 6. THE SECOND NEBULAR EPOCH

6.1. Chondrules thesis, has been taken as support for the X-wind model. However, there are still many proponents of the hot nebula Four chapters in the first edition were devoted to chon- hypothesis, which is consistent with models and observa- drules. New observational, experimental, and theoretical tions of the earliest era of disk formation when mass accre- studies of chondrules have resulted in some changes, many tion rates were high (e.g., Bell et al., 2000). Regardless of of which were detailed in Chondrules and the Protoplane- which model is advocated, it is clear that we envision a tary Disk (Hewins et al., 1996). The presence of C as a re- more dynamic nebula with transient heating events. ducing agent in precursors produces character- Refractory inclusions (CAIs) were described in the first istic mineralogical features of chondrules (Connolly et al., edition as nebular condensates, commonly modified by 1994). Melting intervals for chondrules, previously thought melting, recrystallization, and alteration (Fig. 6). These an- cient objects are now generally understood to be mixtures of condensate materials and refractory residues from evapora- tion (Ireland and Fegley, 2000). High- conden- sation is required to produce the observed fractionations in refractory trace elements, whereas the widespread persis- tence of mass-dependent isotopic fractionation in refractory elements such as Mg and Si indicates evaporation (Gross- man et al., 2002). It is now recognized that the large CAIs in Allende have been extensively processed after accretion and are not representative of CAIs in other meteorite classes. Calcium-aluminum-rich inclusions in other chondrite groups have now been characterized (MacPherson, 2003). Amoeboid olivine aggregates (AOAs) are the most com- mon type of refractory inclusions in many types of carbona- ceous chondrites. Detailed studies of AOAs, which provide a compositional link between CAIs and chondrules, indicate they are clumps of lower-temperature nebula condensates that originated in a 16O-rich gaseous reservoir (Krot et al., 2002b). Smooth, concentric zoning of some FeNi metal grains in primitive CH chondrites suggests their formation Fig. 7. X-ray elemental map in Ni Kα of a zoned FeNi metal by gas- condensation (Meibom et al., 1999). These grain from the Hammadah al Hamra 237 carbonaceous chondrite. grains (Fig. 7) may be the first documented metal conden- This metal grain is inferred to be a nebular condensate. Courtesy sates. of A. Krot, University of Hawai‘i. McSween et al.: Recent Advances in Meteoritics and Cosmochemistry 59

to have lasted for hours, are now restricted to a few min- are dominated by soluble carboxyl and dicarboxyl com- utes, to allow retention of moderately volatile elements pounds but few amino compounds. Its abundant aromatic (Hewins, 1997). Moreover, volatile retention apparently compounds have a more restricted distribution than those requires that chondrules could not have formed in the ca- in other carbonaceous chondrites (Pizzarello et al., 2001), nonical nebula, but must have formed by flash heating at possibly reflecting catalytic processes that tend to be more higher pressures (Yu and Hewins, 1998). Many chondrules selective than other synthetic pathways. Tiny, hollow or- appear to have experienced multiple heating events (Rubin ganic globules (Fig. 8) in Tagish Lake (Nakamura et al., and Krot, 1996), and most were not completely melted. 2002) are similar to material produced by laboratory simula- Correlations between the relative ages, based on 26Al, and tion of UV photolysis of analogs. bulk compositions of chondrules (Mostefaoui et al., 2002) Calculations support the idea that the soluble fraction of suggest that Si and volatile elements evaporated from chon- the organic compounds in chondrites formed during aque- drule melts and then recondensed as precursors for the next ous alteration of parent bodies (Schulte and Shock, 2004). generation of chondrules. Experiments constrain peak tem- Some progress has been made in characterizing the insolu- peratures to 1770–2120 K, and chondrule cooling rates were ble macromolecular organic matter in carbonaceous chon- decidedly nonlinear, very fast and then slow, consistent with drites, cited as a daunting task in the first edition. Similarities shock melting (Desch and Connolly, 2002). The origin of among in CI and CM chondrites suggest chondrules remains enigmatic, but thermal processing of that essentially the same aromatic structural units were com- particles in nebular shock waves appears to meet most con- mon to all (Sephton et al., 1998, 2000). Cody et al. (2002) straints imposed by chondrule properties (Ciesla and Hood, determined that this material in Murchison was 61–66% 2002; Desch and Connolly, 2002). aromatic and that its aliphatic chains are highly branched.

6.2. Metal and Sulfide 6.5. Cosmogenic Nuclides

Metal grains in ordinary chondrites, suggested to be There is continuing disagreement over whether or not condensates in the first edition, have apparently been modi- meteorites show isotopic evidence of irradiation fied after accretion (Zanda et al., 1994). Sulfides in chon- by an energetic early Sun (Woolum and Hohenberg, 1993; drites are now understood to have formed by reaction of Wieler et al., 2000). As noted earlier, however, the discov- metal with the gaseous nebula. Lauretta et al. (1997) de- ery of the former presence of 10Be in refractory inclusions termined that corrosion of FeNi metal by H2S produces Fe- (McKeegan et al., 2000) attests to intense irradiation in the bearing sulfides rapidly enough to occur within the lifetime early solar system. The production by spallation of other of the nebula, and showed that sulfides produced in this way short-lived radionuclides found in chondrites has also been are morphologically similar to those in chondrite matrix. suggested (Gounelle et al., 2001); however, 10Be and 26Al are decoupled in many CAIs (Marhas et al., 2002). Some 6.3. Matrix short-lived nuclides appear to have been produced by spal- lation in the nebular, some by nucleosynthesis in other stars, The of chondrite matrices has become in- and some possibly (but not necessarily) by both processes. creasingly well characterized by application of transmission electron . Matrix is most easily studied in carbo- naceous chondrites (Buseck and Hua, 1993), where it is most abundant. New descriptions of matrix in the most primitive carbonaceous chondrites reveal amorphous silicate material, forsterite, and enstatite, with minor carbonaceous, refrac- tory, and presolar materials — apparently mixtures of nebu- lar materials and interstellar grains. Hydrothermal alteration of such matrix has produced the matrices of most carbona- ceous chondrites. The mineralogy of interstitial matrix and rims on chondrules in unequilibrated ordinary chondrites (Brearley, 1996) is more complex, consisting mostly of oli- vine, sometimes with amorphous silicate material, and py- roxenes, feldspars, metal, a variety of and sulfides, whitlockite, and various alteration phases.

6.4. Organic Compounds

The Tagish Lake meteorite’s fall and clean collection Fig. 8. TEM image of a hollow globule of organic matter (scale under subfreezing conditions make it a relatively uncon- bar = 200 nm) in the Tagish Lake carbonaceous chondrite. Cour- taminated sample. The organic components of Tagish Lake tesy of K. Nakamura, Kobe University. 60 Meteorites and the Early Solar System II

7. THE ACCRETION EPOCH measuring the times of cooling for ordinary chondrites metamorphosed at various peak temperatures (Göpel et al., 7.1. Mixing and Sorting of Nebular Components 1994; Trieloff et al., 2003). Differences in 182Hf-182W and 235U/238U-207Pb/206Pb ages (equal to 2–12 Ma for H chon- Presolar grains constrain mixing between reservoirs in drites) have been used to estimate the interval of ordinary the nebula. The average isotopic compositions of carbon and chondrite metamorphism (Humayun and Campbell, 2002). silicon in SiC grains are the same among different meteor- The chondrite classification system based partly on ther- ite groups, as would be expected if the nebula sampled a mal metamorphic grade was in wide use prior to the first well-mixed reservoir of debris from various stars (Huss and edition but the action of fluids, indicated by changes in oxi- Lewis, 1995; Russell et al., 1997). The limited size distri- dation state during ordinary chondrite metamorphism (Mc- butions of chondrules are now explained as the result of Sween and Labotka, 1993), had not been recognized. Scales aerodynamic sorting in turbulent nebula eddies (Cuzzi et al., quantifying the intensity of aqueous alteration (Browning 1996; Kuebler et al., 1999). et al., 1996) and shock metamorphism (Stöffler et al., 1991; Scott et al., 1992; Rubin et al., 1997) now allow effects 7.2. Sampling Other Accreted Materials accompanying these processes to be discerned. Noteworthy examples are destruction of presolar grains (Huss, 1990), Calculations of IDP orbital evolution show that the at- the redistribution of minor elements in chondritic metal dur- mospheric entry velocity of -derived dust is gener- ing metamorphism (Zanda et al., 1994), and the synthesis ally higher than that of asteroid-derived particles. Entry of new organic compounds during aqueous alteration and velocity controls the degree of atmospheric heating, which, heating (Sephton et al., 2003; Pearson et al., 2002). In the in turn, affects the abundances of 4He (Nier and Schlutter, first edition, aqueous alteration was described only as a par- 1993) and other volatile elements (especially zinc) (Kehm ent-body process, still a prominent view (Krot et al., 1995). et al., 2002), as well as mineralogy (Greshake et al., 1998). However, other observations suggest some carbonaceous These changes can potentially be used to identify IDPs of chondrite components may have been altered before accre- cometary origin. tion, either in the nebula or within small, precursor plane- Micrometeorites are larger than IDPs and are commonly tesimals (Metzler et al., 1992). melted partly or completely during atmospheric passage. Halite-bearing clasts (Fig. 9) have been discovered in The resulting cosmic spherules represent the peak in mass several recently fallen ordinary chondrite regolith breccias distribution of meteoritic materials accreted to Earth, so a (Zolensky et al., 1999). Irradiation effects show that these comprehensive chemical study of them may provide a less- salts are preterrestrial, and fluid inclusions demonstrate that biased sampling of asteroid compositions than do meteor- they formed by precipitation from aqueous at low ites. Most cosmic spherules have CM-chondrite-like com- temperatures in asteroid regoliths (Whitby et al., 2000). positions (Brownlee et al., 1997).

8. THE PARENT BODY EPOCH

The nebular record in meteorites is commonly obscured, at least in part, by parent-body processes — thermal meta- morphism, aqueous alteration, melting, impact brecciation, and shock metamorphism. The first edition devoted six chap- ters to these topics, but ambiguities remained. Significant advances in unraveling these geologic overprints in mete- orites now enable a better understanding of which materi- als and properties are of nebular origin and which are not.

8.1. Chondritic Parent Bodies

All asteroids have been heated to some degree, probably by radioactive decay of short-lived nuclides such as 26Al (MacPherson et al., 1995; Russell et al., 1996; Srinivasan et al., 1999; Kita et al., 2000). Thermal evolution models based on 26Al heating provide a context for interpreting measureable properties in chondrites — equilibration tem- peratures, cooling rates, and radiometric ages (McSween et al., 2002). These models are appropriate for bodies that Fig. 9. Halite crystals (3–4 nm) in the Zag ordinary chondrite develop concentric metamorphic zones, and the existence demonstrate the former presence of evaporating fluids in asteroids. of such “onion-shell” asteroids has been demonstrated by Courtesy of M. Zolensky, NASA Johnson Space Center. McSween et al.: Recent Advances in Meteoritics and Cosmochemistry 61

8.2. Differentiated Parent Bodies Schoenberg et al., 2002; Yin et al., 2002) significantly low- ered the formation ages of Earth (11–30 Ma) and A new development in understanding achondrite mag- (<15 Ma) relative to the formation time of CAIs, suggesting matism is evidence supporting that eucrites and related di- rapid accretion and differentiation of the terrestrial planets. ogenites may have formed in a magma body of asteroidal scale (Righter and Drake, 1997; Ruzicka et al., 1997). 9.2. Organic and Putative Biogenic Substances However, despite extensive petrographic and geochemical studies, there is still little consensus on major questions of Chyba and Sagan (1992) concluded that the dominant petrogenesis (Mittlefehldt et al., 1998). Angrites source of organic material to the early Earth was IDPs, provide an interesting comparison with eucrites, mimick- which are ~10% organics by mass, because their gentle ing the dichotomy of alkaline and tholeiitic basalts on Earth atmospheric deceleration could deliver organic compounds (Mittlefehldt and Lindstrom, 1990). Angrites and eucrites intact. have similar O-isotopic compositions (Clayton and Mayeda, No review of advances in meteoritics or biogenic mol- 1996) and experiments suggest they could have been pro- ecules would be complete without mentioning ALH 84001, duced by melting similar chondritic protoliths under dif- originally misclassified as a but recognized as ferent conditions. The paucity of meteoritic basalt a unique by Mittlefehldt (1994). If for groups relative to other differentiated meteorites might be no other reason, ALH 84001 is important as the oldest explained by volcanism (Wilson and Keil, 1991). (~4.5 Ga) planetary sample (Nyquist et al., 2001). The pro- Ureilites, the most perplexing primitive achondrites, were posal that this meteorite contains evidence of extraterrestrial formerly argued to be cumulates but are now generally life (McKay et al., 1996) generated a firestorm of contro- viewed as smelting residues (Goodrich, 1992; Walker and versy that placed meteoritics on the front pages of news- Grove, 1993; Singletary and Grove, 2003). Supporting the papers. The meteoritics responded with an out- interpretation that the parent body did not undergo pouring of research on carbonates, nanophase magnetites, extensive melting is the surprising finding that ureilites have putative microfossils, and organic compounds. Although primitive O-isotopic compositions that correlate with the Fe few planetary scientists have accepted the proffered evi- contents of olivine and (Clayton and Mayeda, dence for this hypothesis, its lingering effects are a revital- 1988). ized Mars exploration program focused on the search for New information on Fe-Ni phase equilibria, such as a life, as well as a significant increase in the price of mete- revised Fe-Ni phase diagram (Yang et al., 1996), has pro- orites. Scientific consequences include research on the for- vided an improved understanding of the cooling histories mation and stability of polycyclic aromatic hydrocarbons, of asteroid cores. An investigation of Ni-rich areas of wid- recognition of the difficulties in identifying potential min- manstätten patterns in iron meteorites (Yang et al., 1997) eralogic or isotopic and , discovery of indicated these are not , as previously thought, but novel mechanisms for carbonate formation, and acknowl- intergrowths of tetrataenite, martensite, and awaruite. This edgment that terrestrial micro- eventually con- revelation constitutes a drastic revision of iron meteorite taminate all meteorites (Steele et al., 2000). mineralogy, and its implications for Fe-Ni phase relations are not yet clear. Hopfe and Goldstein (2001) have signifi- 9.3. Implications of Cosmic-Ray cantly revised the metallographic cooling rate method. Exposure Ages The difficulties in segregating metallic liquids from host silicates have been clarified (Taylor, 1992). Numerical mod- The large number of exposure ages for different mete- els of fractional crystallization in irons have become more orite groups now available (Wieler and Graf, 2001; Herzog, sophisticated, and now explore the effects of imperfect mix- 2003) permits new insights into the of ing, immiscibility, and trapping of S-rich liquid (Haack . The pronounced age clumps for various groups and McCoy, 2003, and references therein). Application of suggest that a small number of collisions produced a large Re-Os dating has demonstrated that the cores represent- fraction of known meteorites. In the first edition, the reign- ing all the various iron meteorite groups crystallized within ing view was that Earth capture depended on impact injec- 100 m.y. of each other (Smoliar et al., 1996; Shen et al., tion of meteoroids into chaotic . However, the 1996). calculations of Gladman et al. (1997) showed that trans- port through resonances took much less time than clocked 9. THE PLANETARY EPOCH by cosmic-ray exposure ages. The order-of-magnitude dis- crepancies have now been resolved by considering the role 9.1. Formation Chronology of the Yarkovsky effect (small accelerations produced by asymmetric solar heating) in slowly moving meteoroids into The application of 182Hf-182W to iron meteorites and resonances (Farinella et al., 1998). chondrites has constrained the early times of core forma- tion in asteroids (Lee and Halliday, 1997). A revision in the Acknowledgments. Thoughtful reviews by H. Palme and E. W-isotopic composition for chondrites (Kleine et al., 2002; Zinner have improved this chapter. We also thank various indi- 62 Meteorites and the Early Solar System II viduals who provided images, each identified in the respective Clayton R. N., Mayeda T. K., Taliaferri E., Spanding R., captions. MacRae N. D., Hoffman E. L., Mittlefehldt D. W., Wacker J. F., Bird J. A., Campbell M. D., Carpenter R., Gingerich H., REFERENCES Glatiotis M., Greiner E., Mazur M. J., McCausland P. J., Plotkin H., and Mazur T. R. (2000) The fall, recovery, orbit, Alexander C. M. O’D. and Nittler L. R. (1999) The galactic chemi- and composition of the Tagish Lake metorite: A new type of cal evolution of Si, Ti and O isotopes. Astrophys. J., 519, 222– carbonaceous chondrite. , 290, 320–325. 235. Browning L. B., McSween H. Y., and Zolensky M. E. (1996) Allègre C. J., Gerard M., and Göpel C. (1995) The age of the Correlated alteration effects in CM carbonaceous chondrites. Earth. Geochim. Cosmochim. Acta, 59, 1445–1456. Geochim. Cosmochim. Acta, 60, 2621–2633. Allende Prieto C., Lambert D. L., and Asplund M. (2001) The Brownlee D. E., Joswiak D. J., Schlutter D. J., Pepin R. O., Bra- forbidden abundance of in the sun. Astrophys. J. Lett., dley J. P., and Love S. J. (1995) Identification of individual 556, L63–L66. cometary IDPs by thermally stepped He release (abstract). In Allende Prieto C., Lambert D. L., and Asplaund M. (2002) A Lunar and XXVI, pp. 183–184. Lunar and reappraisal of the solar photospheric C/O ratio. Astrophys. J. Planetary Institute, Houston. Lett., 573, L137–L140. Brownlee D. E., Bates B., and Schramm L. (1997) The elemental Amari S., Anders E., Virag A., and Zinner E. (1990) Interstellar composition of stony cosmic spherules. Meteoritics & Planet. graphite in meteorites. Nature, 345, 238–240. Sci., 32, 157–175. Amelin Y., Krot A. N., Hutcheon I. D., and Ulyanov A. A. (2002) Burnett D. S., Woolum D. S., Benjamin T. M., Rogers P. X. Z., Lead isotopic ages of chondrules and calcium-aluminum-rich Duffy C. J., and Maggiore C. (1989) A test of the smoothness inclusions. Science, 297, 1678–1683. of the elemental abundances of carbonaceous chondrites. Geo- Anders E. and Grevesse N. (1989) Abundances of the elements: chim. Cosmochim. Acta, 53, 471–481. Meteoritic and solar. Geochim. Cosmochim. Acta, 53, 197–214. Buseck P. R. and Hua X. (1993) Matrices of carbonaceous chon- Anders E. and Zinner E. (1993) Interstellar grains in primitive drite meteorites. Annu. Rev. Earth Planet. Sci., 21, 255–305. meteorites: Diamond, silicon carbide and graphite. Meteorit- Chyba C. F. and Sagan C. (1992) Endogenous production, exog- ics, 28, 490–514. enous delivery and impact-shock synthesis of organic mole- Bell K. R., Cassen P. M., Wasson J. T., and Woolum D. S. (2000) cules: An inventory for the origins of life. Nature, 355, 125– The FU Orionis phenomenon and solar nebular material. In 132. and Planets IV (V. Manning et al., eds.), pp. 897– Ciesla F. J. and Hood L. L. (2002) The nebular shock wave model 926. Univ. of Arizona, Tucson. for chondrule formation: Shock processing in a particle-gas Benedix G. K., McCoy T. J., Keil K., Bogard D. D., and Garrison suspension. Icarus, 158, 281–293. D. H. (1998) A petrologic and isotopic study of winonaites: Clayton R. N. (2002) Self-shielding in the solar nebula. Nature, Evidence for early partial melting, brecciation, and metamor- 415, 860–861. phism. Geochim. Cosmochim. Acta, 62, 2535–2554. Clayton R. N. and Mayeda T. K. (1988) Formation of ureilites by Bernatowicz T. J. and Zinner E. K. (1997) Astrophysical Impli- nebular processes. Geochim. Cosmochim. Acta, 52, 1313–1318. cations of the Laboratory Study of Presolar Materials. Ameri- Clayton R. N. and Mayeda T. K. (1996) Oxygen isotope studies can Institute of , New York. 750 pp. of achondrites. Geochim. Cosmochim. Acta, 60, 1999–2017. Bernatowicz T. J., Cowsik R., Gibbons P. C., Lodders K., Fegley Cody G. D., Alexander C. M. O’D., and Tera F. (2002) Solid- B., Amari S., and Lewis R. S. (1996) Constraints on stellar state (1H and 13C) nuclear magnetic resonanance spectroscopy grain formation from presolar graphite in the Murchison mete- of insoluble organic in the : A orite. Astrophys. J., 472, 760–782. self-consistent quantitative analysis. Geochim. Cosmochim. Bernatowicz T. J., Messenger S., Pravdivtseva O., Swan P., and Acta, 66, 1851–1865. Walker R. M. (2003) Pristine presolar silicon carbide. Geochim. Connolly H. C., Hewins R. H., Ash R. D., Zanda B., Lofgren Cosmochim. Acta, 67, 4679–4691. G. E., and Bourot-Denise M. (1994) Carbon and the forma- Bischoff A., Palme H., Schultz L., Weber D., Weber H. W., and tion of reduced chondrules. Nature, 371, 136–139. Spettel B. (1993) Acfer 182 and paired samples, an iron-rich Cooper G. W., Thiemens M. H., Jackson T.-L., and Chang S. carbonaceous chondrite: Similarities with ALH85085 and its (1997) Sulfur and isotope anomalies in meteorite relationship to CR chondrites. Geochim. Cosmochim. Acta, 57, sulfonic acids. Science, 277, 1072–1074. 2631–2648. Cronin J. R. and Pizzarello S. (1997) Enantiomeric excesses in Bottke W. F. Jr., Cellino A., Paolicchi P., and Binzel R. P., eds. meteoritic amino acids. Science, 275, 951–955. (2002) Asteroids III. Univ. of Arizona, Tucson. 785 pp. Cuzzi J. N., Dobrovolskis A. R., and Hogan R. C. (1996) Turbu- Bradley J. P. (1994) Chemically anomalous, preaccretionally ir- lence, chondrules, and planetesimals. In Chondrules and the radiated grains in interplanetary dust from comets. Science, (R. H. Hewins et al., eds.), pp. 35–43. 265, 925–929. Cambridge Univ., New York. Bradley J. P., Keller L. P., Brownlee D. E., and Thomas K. L. Desch S. J. and Connolly H. C. (2002) A model of the thermal (1996) Reflectance spectroscopy of interplanetary dust parti- processing of particles in solar nebula shocks: Application to cles. Meteoritics & Planet. Sci., 31, 394–402. the cooling rates of chondrules. Meteoritics & Planet. Sci., 37, Brearley A. J. (1996) The nature of matrix in unequilibrated chon- 183–207. dritic meteorites and its possible relationship to chondrules. In Endress M., Zinner E., and Bischoff A. (1996) Early aqueous Chondrules and the Protoplanetary Disk (R. H. Hewins et al., activity on primitive meteorite parent bodies. Nature, 279, 701– eds.), pp. 137–152. Cambridge Univ., Cambridge. 703. Brown P. G., Hildebrand A. R., Zolensky M. E., Grady M., Engel M. H. and Macko S. A. (1997) Isotopic evidence for extra- McSween et al.: Recent Advances in Meteoritics and Cosmochemistry 63

terrestrial non-racemic amino acids in the Murchison meteorite. ing rate method revised: Application to iron meteorites and Nature, 389, 265–268. . Meteoritics & Planet. Sci., 36, 135–154. Farinella P., Vokrouhlický D., and Hartmann W. (1998) Meteor- Hoppe P. and Zinner E. (2000) Presolar dust grains from meteor- ite delivery via Yarkovsky orbital drift. Icarus, 132, 378–387. ites and their stellar sources. J. Geophys. Res., 105, 10371– Flynn G. J., Keller L. P., Feser M., Wirick S., and Jacobsen C. 10385. (2003) The origin of organic matter in the solar system: Evi- Humayun M. and Clayton R. N. (1995) Potassium isotope cosmo- dence from the interplanetary dust particles. Geochim. Cosmo- chemistry: Genetic implications of volatile element depletion. chim. Acta, 67, 4791–4806. Geochim. Cosmochim. Acta, 59, 2131–2148. Gilmour I. (2003) Structural and isotopic analysis of organic Humayun M. and Campbell A. J. (2002) The duration of ordinary matter in carbonaceous chondrites. In Treatise on Geochemis- chondrite metamorphism inferred from tungsten microdistribu- try, Vol. 1: Meteorites, Comets, and Planets (A. M. Davis, ed.), tion in metal. Earth Planet. Sci. Lett., 198, 225–243. pp. 269–290. Elsevier, Oxford. Huss G. R. (1990) Ubiquitous interstellar diamond and SiC in Gilmour J. D., Whitby J. A., Turner G., Bridges J. C., and primitive chondrites: Abundances reflect metamorphism. Na- Hutchison R. (2000) The iodine-xenon system in clasts and ture, 347, 159–162. chondrules from ordinary chondrites: Implications for early Huss G. R. and Lewis R. S. (1995) Presolar diamond, SiC, and solar system chronology. Meteoritics & Planet. Sci., 35, 445– graphite in primitive chondrites: Abundances as a of 455. meteorite class and petrologic type. Geochim. Cosmochim. Gladman B. J., Migliorini F., Morbidelli A., Zappala V., Michel Acta, 59, 115–160. P., Cellino A., Froeschle C., Levinson H. F., Bailey M., and Ireland T. R. and Fegley B. Jr. (2000) The solar system’s earliest Duncan M. (1997) Dynamical lifetimes of objects injected into chemistry: Systematics of refractory inclusions. Intern. Geol. asteroid belt resonances. Science, 277, 197–201. Rev., 42, 865–894. Goodrich C. A. (1992) Ureilites: A critical review. Meteoritics, Kallemeyn G. W., Rubin A. E., and Wasson J. T. (1991) The com- 27, 327–352. positional classification of chondrites: V. The Karoonda (CK) Goodrich C. A. and Delaney J. S. (2000) Fe/Mg-Fe/Mn relations group of carbonaceous chondrites. Geochim. Cosmochim. Acta, of meteorites and primary heterogeneity of primitive achon- 55, 881–892. drite parent bodies. Geochim. Cosmochim. Acta, 64, 149–160. Kallemeyn G. W., Rubin A. E., and Wasson J. T. (1996) The com- Göpel C., Manhes G., and Allègre C. J. (1994) U-Pb systematics positional classification of chondrites: VII. The R chondrite of phosphates from equilibrated ordinary chondrites. Earth group. Geochim. Cosmochim. Acta, 60, 2243–2256. Planet. Sci. Lett., 121, 153–171. Kehm K., Flynn G. J., Sutton S. R., and Hohenberg C. M. (2002) Gounelle M. and Zolensky M. E. (2001) A terrestrial origin for Combined noble gas and trace element measurements on indi- sulfate veins in CI1 chondrites. Meteoritics & Planet. Sci., 36, vidual stratospheric interplanetary dust particles. Meteoritics 1321–1329. & Planet. Sci., 37, 1323–1335. Gounelle M., Shu f. H., Shang H., Glassgold A. E., Rehm K. E., Kerridge J. F. and Matthews M. S., eds. (1988) Meteorites and and Lee T. (2001) Extinct radioactivities and protosolar cos- the Early Solar System. Univ. of Arizona, Tucson. 1268 pp. mic rays: Self-shielding and light elements. Astrophys. J., 548, Keller L. P., Messenger S., Flynn G. J., Clemett S., Wirick S., 1051–1070. and Jacobsen C. (2004) The nature of molecular cloud mate- Greenwood R. C., Kearsley A. T., and Franchi I. A. (2003) Are rial in interplanetary dust. Geochim. Cosmochim. Acta, 68, CK chondrites really a distinct group or just equilibrated CVs? 2577–2589. (abstract). Meteoritics & Planet. Sci., 38, A96. Kimura M., Hiyagon H., Palme H., Spettel B., Wolf D., Clayton Greshake A., Klock W., Arndt P., Maetz M., Flynn G. J., Bajt S., R. N., Mayeda T. K., Sato T., Suzuki T., and Kojima H. (2002) and Bischoff A. (1998) Heating experiments simulating atmo- Anomalous H-chondrites, Y792947, Y93408 and Y82038, with spheric entry heating of micrometeorites: Clues to their par- abundant refractory inclusions and very low metamorphic ent body sources. Meteoritics & Planet. Sci., 33, 267–290. grade. Meteoritics & Planet. Sci., 37, 1417–1434. Grossman J. N., Rubin A. E., and MacPherson G. J. (1988) ALH Kita N. T., Nagahara H., Togashi S., and Morishita T. (2000) A 85085: A unique volatile-poor carbonaceous chondrite with short duration of chondrule formation in the solar nebula: possible implications for nebular fractionation processes. Earth Evidence from 26Al in Semarkona ferromagnesian chondrules. Planet. Sci. Lett., 91, 33–54. Geochim. Cosmochim. Acta, 64, 3913–3922. Grossman L., Ebel D. S., and Simon S. B. (2002) Formation of Kita N. T., Ikeda Y., Togashi S., Liu Y., Morishita Y., and Weisberg refractory inclusions by evaporation of condensate precursors. M. K. (2004) Origin of ureilites inferred from a SIMS oxygen Geochim. Cosmochim. Acta, 66, 145–161. isotopic and trace element study of clasts in the Dar al Gani Haack H. and McCoy T. J. (2003) Iron and stony-iron meteorites. 319 polymict ureilite. Geochim. Cosmochim. Acta, 68, 4213– In Treatise on , Vol. 1: Meteorites, Comets, and 4235. Planets (A. M. Davis, ed.), pp. 325–345. Elsevier, Oxford. Kleine T., Munker C., Mezger K., and Palme H. (2002) Rapid Herzog G. F. (2003) Cosmic-ray exposure ages of meteorites. In accretion and early core formation on asteroids and the terres- Treatise on Geochemistry, Vol. 1: Meteorites, Comets, and trial planets from Hf-W chronometry. Nature, 418, 952–955. Planets (A. M. Davis, ed.), pp. 347–380. Elsevier, Oxford. Krot A. N., Scott E. R. D., and Zolensky M. E. (1995) - Hewins R. H. (1997) Chondrules. Annu. Rev. Earth Planet. Sci., ogical and chemical modification of components in CV3 chon- 25, 61–83. drites: Nebular or asteroidal processing? Meteoritics, 30, 748– Hewins R. H., Jones R. H., and Scott E. R. D., eds. (1996) Chon- 775. drules and the Protoplanetary Disk. Cambridge Univ., New Krot A. N., Meibom A., Weisberg M. K., and Keil K. (2002a) The Yor k. CR chondrite clan: Implications for early solar system pro- Hopfe W. D. and Goldstein J. I. (2001) The metallographic cool- cesses. Meteoritics & Planet Sci., 37, 1451–1490. 64 Meteorites and the Early Solar System II

Krot A. N., McKeegan K. D., Leshin L. A., MacPherson G. J., Meibom A. and Clark B. E. (1999) Evidence for the insignificance and Scott E. R. D. (2002b) Existence of a 16O-rich gaseous of ordinary chondritic material in the asteroid belt. Meteorit- reservoir in the solar nebula. Science, 295, 1051–1054. ics & Planet. Sci., 34, 7–24. Kuebler K. E., McSween H. Y., Carlson W. D., and Hirsch D. Meibom A., Pataev M. I., Krot A. N., Wood J. A., and Keil K. (1999) Sizes and of chondrules and metal- grains (1999) Primitive FeNi metal grains in CH carbonaceous chon- in ordinary chondrites: Possible implications for nebular sort- drites formed by condensation from a gas of solar composi- ing. Icarus, 141, 96–106. tion. J. Geophys. Res., 104, 22053–22059. Lauretta D. S., Lodders K., and Fegley B. (1997) Experimental Mendybaev R. A., Beckett J. R., Grossman L., Stolper E., Coo- simulations of sulfide-formation in the solar nebula. Science, per R. F., and Bradley J. P. (2002) Volatilization kinetics of 277, 358–360. silicon carbide in reducing : An experimental study with Lee D.-C. and Halliday A. N. (1997) Hf-W isotopic evidence for applications to the survival of presolar grains in the solar rapid accretion and differentiation in the early solar system. nebula. Geochim. Cosmochim. Acta, 66, 661–682. Science, 274, 1876–1879. Messenger S. (2000) Identification of molecular-cloud material in Lewis, R. S., Amari S., and Anders E. (1990) Meteoritic silicon interplanetary dust particles. Nature, 404, 968–971. carbide: Pristine material from carbon stars. Nature, 348, 293– Messenger S., Keller L. P., Stademann F. J., Walker R. M., and 298. Zinner E. (2003) Samples of stars beyond the solar system: Lodders K. (2003) Solar system abundances and condensation Silicate grains in interplanetary dust. Science, 300, 105–108. temperatures of the elements. Astrophys. J., 591(2), 1220–1247. Metzler K., Bishoff A., and Stoffler D. (1992) Accretionary dust Lugmair G. W. and Shukolyukov A. (2001) Early solar system mantles in CM chondrites: Evidence for solar nebula pro- events and timescales. Meteoritics & Planet. Sci., 36, 1017– cesses. Geochim. Cosmochim. Acta, 56, 2873–2897. 1026. Mittlefehldt D. W. (1994) ALH84001, a cumulate MacPherson G. J. (2003) Calcium-aluminum-rich inclusions in member of the martian meteorite clan. Meteoritics, 29, 214– chondritic meteorites. In Treatise on Geochemistry, Vol. 1: 221. Meteorites, Comets, and Planets (A. M. Davis, ed.), pp. 201– Mittlefehldt D. W. (2002) Geochemistry of the ungrouped carbon- 246. Elsevier, Oxford. aceous chondrite Tagish Lake, the anomalous CM chondrite MacPherson G. J., Davis A. M., and Zinner E. K. (1995) The Bells, and comparison with CI and CM chondrites. Meteorit- distribution of Al-26 in the early solar system — a reappraisal. ics & Planet. Sci., 37, 703–712. Meteoritics, 30, 365–386. Mittlefehldt D. W. and Lindstrom M. M. (1990) Geochemistry and MacPherson G. J., Huss G. R., and Davis A. M. (2003) Extinct genesis of the angrites. Geochim. Cosmochim. Acta, 54, 3209– 10Be in type A calcium-aluminum-rich inclusions from CV 3218. chondrites. Geochim. Cosmochim. Acta, 67, 3165–3179. Mittlehehldt D. W., McCoy T. J., Goodrich C. A., and Kracher Marhas K. K., Goswami J. N., and Davis A. M. (2002) Short-lived A. (1998) Non-chondritic meteorites from asteroidal bodies. nuclides in hibonite grains from Murchison: Evidence for solar In Planetary Materials (J. J. Papike, ed.), pp. 4-1 to 4-195. system evolution. Science, 298, 2182–2184. Reviews in Mineralogy, Vol. 36, Mineralogical Society of McCoy T. J., Keil K., Clayton R. N., Mayeda T. K., Bogard D. D., America. Garrison D. H., Huss G. R., Hutcheon I. D., and Wieler R. Moustefaoui S., Kita N. T., Togashi S., Tachibana S., Nagahara (1996) A petrologic, chemical, and isotopic study of Monu- H., and Morishita Y. (2002) The relative formation ages of ment Draw and comparison with other acapulcoites: Evidence ferromagnesian chondrules inferred from their initial 26Al/27Al. for formation by incipient partial melting. Geochim. Cosmo- Meteoritics & Planet. Sci., 37, 421–438. chim. Acta, 60, 2681–2708. Nakamura K., Zolensky M. E., Tomita S., Nakashima S., and McCoy T. J., Keil K., Clayton R. N., Mayeda T. K., Bogard D. D., Tomeoka K. (2002) Hollow organic globules in the Tagish Garrison D. H., and Wieler R. (1997) A petrologic study of Lake meteorite as possible products of primitive organic reac- lodranites: Evidence for early formation as partial melt resi- tions. Intern. J. Astrobiol., 1, 179–189. dues from heterogeneous precursors. Geochim. Cosmochim. Nehru C. E., Prinz M., Weisberg M. K. Ebihara M. E., Clayton Acta, 61, 623–637. R. N., and Mayeda T. K. (1992) Brachintes: A new primitive McKay D. S., Gibson E. K., Thomas-Keprta K. L., Vali H., achondrite group (abstract). Meteoritics, 27, 267. Romanek C. S., Clemett S. J., Chelier X. D. F., Maechling Nguyen A. and Zinner E. (2004) Discovery of ancient silicate C. R., and Zare R. N. (1996) Search for past : Pos- stardust in a meteorite. Science, 303, 1496–1499. sible relic biogenic activity in Martian meteorite ALH84001. Nier A. O. and Schlutter D. J. (1993) The thermal history of in- Science, 273, 924–930. terplanetary dust particles collected in the Earth’s stratosphere. McKeegan K. D. and Davis A. (2004) Early solar system chro- Meteoritics, 28, 675–681. nology. In Treatise on Geochemistry, Vol. 1: Meteorites, Com- Nittler L. R. (2003) Presolar stardust in meteorites: Recent ad- ets, and Planets (A. M. Davis, ed.), pp. 431–460. Elsevier, vances and scientific frontiers. Earth Planet. Sci. Lett., 209, Oxford. 259–273. McKeegan K. D., Chaussidon M., and Robert F. (2000) Incorpora- Nittler L. R., Alexander C. M. O’D., Gao X., Walker R. M., and tion of short-lived 10Be in a calcium-aluminum-rich inclusion Zinner E. (1997) Stellar : The properties and origins

from the . Science, 289, 1334–1337. of presolar Al2O3 in meteorites. Astrophys. J., 483, 475–495. McSween H. Y. and Labotka T. C. (1993) Oxidation during meta- Nyquist L. E., Bogard D. D., Shih C.-Y., Greshake A., Stoffler morphism of the ordinary chondrites. Geochim. Cosmochim. D., and Eugster O. (2001) Ages and geologic histories of mar- Acta, 57, 1105–1114. tian meteorites. Space Sci. Rev., 96, 105–164. McSween H. Y., Ghosh A., Grimm R. E., Wilson L., and Young Ott U. (1993) Interstellar grains in meteorites. Nature, 364, 25–33. E. D. (2002) Thermal evolution models of asteroids. In Aster- Ott U. and Begemann F. (2000) Spallation recoil and age of oids III (W. F. Bottke Jr. et al., eds.), pp. 559–571. Univ. of presolar grains in meteorites. Meteoritics & Planet. Sci., 35, Arizona, Tucson. 53–63. McSween et al.: Recent Advances in Meteoritics and Cosmochemistry 65

Palme H. (2001) Chemical and isotopic heterogeneity in protosolar meteorite. Geochim. Cosmochim. Acta, 62, 1821–1828. matter. Philos. Trans. R. Soc., 359, 2061–2075. Sephton M. A., Pillinger C. T., and Gilmour I. (1999) Small-scale Palme H. and Jones A. (2003) Solar system abundances of the hydrous pyrolysis of macromolecular material in meteorites. elements. In Treatise on Geochemistry, Vol. 1: Meteorites, Planet. Space Sci., 47, 181–187. Comets, and Planets (A. M. Davis, ed.), pp. 41–61. Elsevier, Sephton M. A., Pillinger C. T., and Gilmour I. (2000) Aromatic Oxford. moieties in meteoritic macromolecular materials: Analysis by Pearson V. K., Sephton M. A., Kearsley A. T., Bland P. A., Franchi hydrous pyrolysis and δ13C of individual compounds. Geo- I. A., and Gilmour I. (2002) Clay mineral — organic matter chim. Cosmochim. Acta, 64, 321–328. relationships in the early solar system. Meteoritics & Planet. Sephton M. A., Verchovsky A. B., Bland P. A., Gilmour I., Grady Sci., 37, 1829–1833. M. M., and Wright I. P. (2003) Investigating variations in car- Pizzarello S., Huang Y., Becker L., Roreda R. J., Nieman R. A., bon and isotopes in carbonaceous chondrites. Geo- Cooper G., and Williams M. (2001) The organic content of chim. Cosmochim. Acta, 67, 2093–2108. the Tagish Lake meteorite. Science, 293, 2236–2239. Shen J. J., Papanastassiou D. A., and Wasserburg G. J. (1996) Richter K. and Drake M. J. (1997) A magma on Vesta: Core Precise Re-Os determinations and systematics of iron meteor- formation and petrogenesis of eucrites and . Mete- ites. Geochim. Cosmochim. Acta, 60, 2887–2900. oritics & Planet. Sci., 32, 929–944. Shu F. H., Shang H., and Lee T. (1996) Toward an astrophysical Rietmeijer F. J. M. (1998) Interplanetary dust particles. In Plane- model of chondrites. Science, 271, 1545–1552. tary Materials (J. J. Papike, ed.), pp. 2-1 to 2-95. Reviews in Shukolyukov A. and Lugmair G. W. (1993) Live iron-60 in the Mineralogy, Vol. 36, Mineralogical Society of America. early solar system. Science, 259, 1138–1142. Rubin A. E. and Kallemeyn G. W. (1994) Pecora Escarpment Simon S. B. and Grossman L. (2003) Petrography and mineral 91002: A member of the new Rumuruti (R) chondrite group. chemistry of the anhydrous component of the Tagish Lake car- Meteoritics, 29, 255–264. bonaceous chondrite. Meteoritics & Planet. Sci., 38, 813–825. Rubin A. E. and Krot A. N. (1996) Multiple heating of chondrules. Singletary S. J. and Grove T. L. (2003) Early petrologic processes In Chondrules and the Protoplanetary Disk (R. H. Hewins et on the ureilite parent body. Meteoritics & Planet. Sci., 38, 95– al., eds.), pp. 173–180. Cambridge Univ., New York. 108. Rubin A. E., Keil K., and Scott E. R. D. (1997) Shock metamor- Smoliar M. I., Walker R. J., and Morgan J. W. (1996) Re-Os ages phism of enstatite chondrites. Geochim. Cosmochim. Acta, 61, of group IIA, IIIA, IVA, and IVB iron meteorites. Science, 271, 847–858. 1099–1102. Rubin A. E., Kallemeyn G. W., Wasson J. T., Clayton R. N., Srinivasan G., Ulyanov A. A., and Goswami J. N. (1994) 41Ca in Mayeda T. K., Grady M., Verchovsky A. B., Eugster O., and the early solar system. Astrophys. J. Lett., 431, L67–L70. Lorenzetti S. (2003) Formation of metal and silicate globules Srinivasan G., Goswami J. N., and Bhandari N. (1999) 26Al in in Gujba: A new Bencubbin-like . Geochim. Cos- eucrite Piplia Kalan: Plausible heat source and formation chro- mochim. Acta, 67, 3283–3298. nology. Science, 284, 1348–1350. Russell S. S., Srinivasan G., Huss G. R., Wasserburg G. J., and Steele A., Goddard D. T., Stapleton D., Toporski J. K. W., Peters MacPherson G. J. (1996) Evidence for widespread 26Al in the V., Bassinger V., Sharples G., Wynn-Williams D. D., and solar nebula and constraints for nebula time scales. Science, McKay D. S. (2000) Investigations into an unknown 273, 757–762. on the martian meteorite . Meteoritics & Russell S. S., Ott U., Alexander C. M., Zinner E. K., Arden J. W., Planet. Sci., 35, 237–241. and Pillinger C. T. (1997) Presolar silicon carbide from the Stöffler D., Keil K., and Scott E. R. D. (1991) Shock metamor- Indarch (EH4) meteorite: Comparison with silicon carbide phism of ordinary chondrites. Geochim. Cosmochim. Acta, 55, populations from other meteorite classes. Meteoritics & Planet. 3845–3867. Sci., 32, 719–732. Swindle T. D., Davis A. M., Hohenberg C. M., MacPherson G. J., Ruzicka A., Snyder G. A., and Taylor L. A. (1997) Vesta as the and Nyquist L. E. (1996) Formation times of chondrules and , eucrite and diogenite parent body: Implications for Ca-Al-rich inclusions: Constraints from short-lived radionu- the size of a core and for large-scale differentiation. Meteorit- clides. In Chondrules and the Protoplanetary Disk (R. H. ics & Planet. Sci., 32, 825–840. Hewins et al., eds.), pp. 77–86. Cambridge Univ., Cambridge. Schoenberg R., Kamber B. S., Collerson K. D., and Eugster O. Tachibana S. and Huss G. R. (2003) The initial abundance of 60Fe (2002) New W-isotope evidence for rapid terrestrial accretion in the solar system. Astrophys. J. Lett., 588, L41–L44. and very early core formation. Geochim. Cosmochim. Acta, 66, Tang M. and Anders E. (1988) Interstellar silicon carbide: How 3151–3160. much older than the solar system? Astrophys. J. Lett., 335, Schulte M. and Shock E. (2004) Coupled and L31–L34. mineral alteration on meteorite parent bodies. Meteoritics & Taylor G. J. (1992) Core formation in asteroids. J. Geophys. Res., Planet. Sci., 39, 1577–1590. 97, 14717–14726. Schulze H., Bischoff A., Palme H., Spettel B., Dreibus G., and Theimens M. H. (1996) Mass-independent isotopic effects in Otto J. (1994) Mineralogy and chemistry of Rumuruti: The chondrites: The role of chemical processes. In Chondrules and first meteorite fall of the new Rumuruti group. Meteoritics, 29, the Protoplanetary Disk (R. H. Hewins et al., eds.), pp. 107– 275–286. 118. Cambridge Univ., Cambridge. Scott E. R. D. (1988) A new kind of primitive achondrite, Allan Trieloff M., Jessberger E. K., Herrwerth I., Hopp J., Fleni C., Hills 85085. Earth Planet. Sci. Lett., 91, 1–18. Ghells M. Bourot-Denise M., and Pellas P. (2003) Structure Scott E. R. D., Keil K., and Stoffler E. (1992) Shock metamor- and thermal history of the H-chondrite parent asteroid revealed phism of carbonaceous chondrites. Geochim. Cosmochim. Acta, by thermochronometry. Nature, 422, 502–506. 56, 4281–4293. Walker D. and Grove T. (1993) Ureilite smelting. Meteoritics, 28, Sephton M. A., Pillinger C. T., and Gilmour I. (1998) δ13C of free 629–636. and macromolecular polyaromatic structures in the Murchison Walker R. J., Horan M. F., Morgan J. W., Becker H., Grossman 66 Meteorites and the Early Solar System II

J. N., and Rubin A. E. (2002) Comparative 187Re-187Os sys- Yang C.-W., Williams D. B., and Goldstein J. I. (1996) A revi- tematics of chondrites: Implications regarding early solar sys- sion of the Fe-Ni phase diagram at low temperatures (<400°C). tem processes. Geochim. Cosmochim. Acta, 66, 4187–4201. J. Phase Equilibria, 17, 522–531. Weisberg M. K., Prinz M., Clayton R. N., and Mayeda T. K. Yang C.-W., Williams D. B. and Goldstein J. I. (1997) Low-tem- (1993) The CR (Rennazo-type) carbonaceous chondrite group perature phase decomposition in metal from iron, stony-iron and its implications. Geochim. Cosmochim. Acta, 57, 1567– and stony meteorites. Geochim. Cosmochim. Acta, 61, 2943– 1586. 2956. Weisberg M. K., Prinz M., Clayton R. N., and Mayeda T. K. Yin Q., Jacobsen S. B., Yamashita K., Blichert-Toft J., Telouk P., (2001) A new metal-rich chondrite grouplet. Meteoritics & and Albarede F. (2002) A short timescale for terrestrial planet Planet. Sci., 36, 401–418. formation from Hf-W chronometry of meteorites. Nature, 418, Weyer S., Munker C., and Mezger K. (2003) Nb/Ta, Zr/Hf and 949–952. REE in the depleted mantle: Implications for the differentia- Young E. D. (2000) Assessing the implications of K isotope cos- tion history of the crust-mantle system. Earth Planet. Sci. Lett., mochemistry for evaporation in the preplanetary solar nebula. 205, 309–324. Earth Planet. Sci. Lett., 183, 321–333. Whitby J., Burgess R., Turner G., Gilmour J., and Bridges J. Young E. D. and Russell S. S. (1998) Oxygen reservoirs in the (2000) Extinct 129I in halite from a primitive meteorite: Evi- early solar nebula inferred from Allende CAI. Science, 282, dence for evaporite formation in the early solar system. Sci- 452–455. ence, 288, 1819–1821. Yu Y. and Hewins R. H. (1998) Transient heating and chondrule Wieler R. and Graf T. (2001) exposure history of formation: Evidence from loss in flash heating simu- meteorites. In Accretion of Extraterrestrial Material on Earth lation experiments. Geochim. Cosmochim. Acta, 62, 159–172. over Time (B. Peucker-Ehrenbrink. and B. Schmitz, eds.), Zanda B., Bourot-Denise M., Perron C., and Hewins R. H. (1994) pp. 221–240. Kluwer Academic/Plenum, New York. Origin and metamorphic redistribution of silicon, chromium, Wieler R., Pedroni A., and Leya I. (2000) Cosmogenic in and phosphorus in the metal of chondrites. Science, 265, 1846– mineral separates from Kapoeta: No evidence for an irradia- 1849. tion of its parent body regolith by an early active Sun. Mete- Zinner E. (1998) Stellar nucleosynthesis and the isotopic compo- oritics & Planet. Sci., 35, 251–257. sition of presolar grains from primitive meteorites. Annu. Rev. Wilson L. and Keil K. (1991) Consequences of explosive erup- Earth Planet. Sci., 26, 147–188. tions on small bodies: The case of the missing basalts on the Zolensky M. E., Bodnar R. J., Gibson E. K., Nyquist L. E., Reese parent body. Earth Planet. Sci. Lett., 104, 505–512. Y., Shih C.-Y., and Wiesmann H. (1999) Asteroidal Woolum D. S. and Hohenberg C. (1993) Energetic particle en- within fluid-inclusion-bearing halite in an H5 chondrite, Mona- vironment in the early solar system — extremely long pre- hans. Science, 285, 1377–1379. compaction meteoritic ages or an enhanced particle flux. In Zolensky M. E., Nakamura K., Gounelle M., Mikouchi T., Kasama Protostars and Planets III (E. H. Levy and J. I. Lunine, eds.), T., Tachikawa O., and Tonui E. (2002) Mineralogy of Tagish pp. 903–919. Univ. of Arizona, Tucson. Lake: An ungrouped type 2 carbonaceous chondrite. Meteor- Yamaguchi A., Clayton R. N., Mayeda T. K., Ebihara M., Oura itics & Planet. Sci., 27, 737–761. Y., Miura Y. N., Haramura H., Misawa K., Kojima H., and Nagao K. (2002) A new source of basaltic meteorites inferred from Northwest Africa 011. Science, 296, 334–336.