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In this work, we present the application of the uranium, thorium–helium (U,Th–He) dating method to two different types of gold objects: geologic gold deposits and archeological gold objects. Direct dating of geologic gold deposits is difficult without assuming contemporaneity between gold and datable hydrothermal minerals. We show that our results indicate that the applied dating method opens a new perspective for the dating of gold deposits without assuming contemporaneity between gold and datable hydrothermal minerals. The second application of our dating method is authenticating archeological gold objects. This is a major problem, as gold is probably the most difficult material in terms of detecting modern forgeries. The feasibility of this application was mentioned in 1996 in an earlier article in Gold Bulletin, Eugster (Gold Bull 29:101–104, 1996). In the past two decades, we applied the U,Th–He dating method to numerous gold antiquities in order to determine the time of their formation or their latest melting process, respectively. Gold always contains traces of uranium and thorium that produce alpha particles by radioactive decay which transform to helium. When gold is molten to manufacture an art object, the helium is lost, but gets stored again when the gold cools down. Thus, the radioactive clock starts anew. Here, we present the results for direct dating of gold deposits and for the authentication of some of the most remarkable artifacts and describe their history.

New analytical developments have made radiogenic helium ( 4 He) applicable to archeological gold artifacts for age determinations. Here we report the application of the U/Th– 4 He method to the direct dating of gold from the historically important gold deposit in Diamantina, Minas Gerais, Brazil. The U/Th– 4 He age of 515 ± 55 Ma for the Diamantina gold is corroborated by a new U/Pb age of 524 ± 16 Ma for rutile recovered from auriferous pockets. These ages tie the Diamantina gold mineralization to the Brasiliano orogenic event, in the context of the Gondwana amalgamation. Our results indicate that U/Th– 4 He dating of gold is possible, opening new perspectives for the dating of gold deposits without assuming contemporaneity between gold and datable hydrothermal minerals.

Forgeries of ancient gold objects are prevalent in almost every collection and some public exhibitions in the past have been exposed as containing forgeries to an embarrassing extent. This situation comes from the fact that it is sometimes impossible to unequivocally recognize forgeries based on their patina or manufacturing and decoration characteristics. We demonstrate that for 13 ancient gold objects the time of their last melting process can be estimated using the U,Th- 4 He dating technique. The extremely small quantities of radiogenic 4 He found, due to the young age and small sample size, require the use of a specially designed ultrasensitive mass spectrometer. We show that the proposed method is a powerful, and the only, quantitative tool in archaeometry for discriminating between fake and genuine ancient gold objects.

We analyzed the spallogenic, trapped, fissiogenic and radiogenic noble gas components in various bulk samples of the angrites D’Orbigny and Sahara 99555 as well as in glass separates of D’Orbigny. The D’Orbigny glass samples show hints of solar-like noble gases, as deduced from the trapped elemental and Ne isotopic compositions; the bulk samples do not contain detectable amounts of trapped gases. These observations indicate that D’Orbigny experienced a complex history shortly after its formation 4.56 Ga ago. The glass of D’Orbigny most likely represents magma that rose from the interior of the angrite parent body (APB) and was quenched near the surface. Hence, the APB may contain—similar to the interior of Earth and Mars—solar noble gases. This would call into question the suggested trapping mechanism for solar noble gases in the Earth and Mars, which involves the solution of early atmospheres into magma oceans, due to the APB’s inability to retain a primordial atmosphere. The first detection of—possibly parentless—radiogenic excess 129 Xe and solar noble gases in the glass of D’Orbigny indicates that the interior of APB degassed to a lesser degree than the outer regions. Therefore primordially trapped, fossil 129 I was kept. The APB was not completely devolatilized. Sahara 99555 yields a cosmic-ray exposure age of 6.8 ± 0.3 Ma, while D’Orbigny was exposed to cosmic rays for 11.9 ± 1.2 Ma. Both ages are different than those found in the other angrites. Hence, the angrites analyzed so far sampled surface material from the APB that was ejected in at least five events. In contrast to the bulk sample, the D’Orbigny glass separates yield concordant ages of only 3.0 ± 1.1 Ma, apparently suggesting a pre-exposure of the host material. However, such a scenario is unlikely, due to very similar Mn–Cr ages found in the bulk and glass of D’Orbigny. Most likely, this discrepancy is the result of additional, secondary gas-free glass. Such glass might have been formed during the meteorite’s entry into the Earth’s atmosphere. Isotopically anomalous Xe due to the decay of 247 Cm has not been found. The presence of 247 Cm in glass of D’Orbigny has been suggested based on Pb isotope constraints.

The iron meteorite Shisr 043 is a single mass of 8267 g found in the south Oman desert 42 km NE of the Shisr village. It is the first iron identified among the >1400 individual meteorites reported from Oman. The meteorite is a slightly elongated mass showing only minor rusting, a partially smooth and partially rough surface with octahedral cleavage, and a partially preserved metallic fusion crust typically 0.75 mm thick. The undeformed Widmanstatten pattern with a mean kamacite bandwidth of 1.0 0.1 mm (n = 97) indicates structural classification as a medium octahedrite. From the bulk composition, Ni = 8.06 wt%, Ga = 18.8 ppm, Ge = 37.25 ppm, and Ir = 3.92 ppm, the meteorite is classified as IIIAB, the most common group of iron meteorites. The cosmic-ray exposure (CRE) age based on 3He, 21Ne, 38Ar concentrations and 10Be-21Ne, 26Al-21Ne, and 36Cl-36Ar ratios is 290 ± 20 Ma. This age falls within the range observed for type IIIAB iron meteorites, but does not coincide with the main cluster. The cosmogenic noble gas and radionuclide data indicate that Shisr 043 had a relatively small preatmospheric mass. The low degree of weathering is consistent with a young terrestrial age of

An impressive daylight fireball was observed from Spain, Portugal, and the south of France at 16h46m45s UTC on January 4, 2004. The meteoroid penetrated into the atmosphere, generating shock waves that reached the ground and produced audible booms. The associated airwave was recorded at a seismic station located 90 km north of the fireball trajectory in Spain, and at an infrasound station in France located 750 km north-east of the fireball. The absolute magnitude of the bolide has been determined to be -18 ± 1 from a casual video record. The energy released in the atmosphere determined from photometric, seismic, and infrasound data was about 0.02 kilotons (kt). A massive fragmentation occurred at a height of 28 ± 0.2 km, resulting in a meteorite strewn field of 20 ± 6 km. The first meteorite specimen was found on January 11, 2004, near the village of Villalbeto de la Pena, in northern Palencia (Spain). To date, about 4.6 kg of meteorite mass have been recovered during several recovery campaigns. The meteorite is a moderately shocked (S4) L6 ordinary chondrite with a cosmic-ray-exposure age of 48 ± 5 Ma. Radioisotope analysis shows that the original body had a mass of 760 ± 150 kg, which is in agreement with the estimated mass obtained from photometric and seismic measurements.

We determined the He, Ne, and Ar isotopic abundances in the four acapulcoites Dhofar (DHO) 125, DHO 290, DHO 312, and Graves Nunataks 98028, the metal-rich diogenite Northwest Africa (NWA) 1982, and a unique achondrite, NWA 1058, that resembles the acapulcoites in its chemical composition. The noble gases in these meteorites consist of three components: trapped gases, cosmic-ray produced nuclides, and nuclides produced by K, Th, and U decay. The four acapulcoites yield cosmic-ray exposure (CRE) ages in the range of 5.0–5.7 Ma and confirm earlier conclusions concerning break-up of all acapulcoites from a common S-type parent asteroid, possibly in three events 4.9, 5.9, and 14.8 Ma ago. We also discuss the other characteristics (mineralogy, chemistry, formation ages, and oxygen and trapped noble gas isotopes) of all other acapulcoites and their relatives, the lodranites. We propose that the acapulcoite/lodranite parent asteroid had a shell structure similar to that of the H chondrites: The less metamorphosed acapulcoites correspond to the H3 and H4 chondrites and originate from the exterior layers, whereas the more severely metamorphosed lodranites, similar to the H5 and H6 chondrites, represent the inner regions of their parent body. Ungrouped achondrite NWA 1982, probably a diogenite, shows a CRE age of 18.9 ± 2.0 Ma that falls on the major exposure age cluster of the diogenites. The unique achondrite NWA 1058 differs in cosmic-ray exposure age (38.9 ± 4.0 Ma) and in oxygen-isotopic composition from the acapulcoites and lodranites and is probably a winonaite.

Gujba is a coarse-grained meteorite fall composed of 41 vol% large kamacite globules, 20 vol% large light-colored silicate globules with cryptocrystalline, barred pyroxene and barred olivine textures, 39 vol% dark-colored, silicate-rich matrix, and rare refractory inclusions. Gujba resembles Bencubbin and Weatherford in texture, oxygen-isotopic composition and in having high bulk delta N-15 values (approximately +685%0). The He-3 cosmic-ray exposure age of Gujba (26 +/- 7 Ma) is essentially identical to that of Bencubbin, suggesting that they were both reduced to meter-size fragments in the same parent-body collision. The Gujba metal globules exhibit metal-troilite quench textures and vary in their abundances of troilite and volatile siderophile elements. We suggest that the metal globules formed as liquid droplets either via condensation in an impact-generated vapor plume or by evaporation of preexisting metal particles in a plume. The lower the abundance of volatile elements in the metal globules, the higher the globule quench temperature. We infer that the large silicate globules also formed from completely molten droplets; their low volatile-element abundances indicate that they also formed at high temperatures, probably by processes analogous to those that formed the metal globules. The coarse-grained Bencubbin-Weatherford-Gujba meteorites may represent a depositional component from the vapor cloud enriched in coarse and dense particles. A second class of Bencubbin-like meteorites (represented by Hammadah a1 Hamra 237 and QUE 94411) may be a finer fraction derived from the same vapor cloud

We determined the mineralogical and chemical characteristics and the He, Ne, and Ar isotopic abundances of 2 meteorites that fell in China and of 2 meteorites that were recovered by the 15th Chinese Antarctic Research Expedition. Guangmingshan (H5), Zhuanghe (H5), and Grove Mountain (GRV) 98002 (L5) yield cosmic ray exposure (CRE) ages of 68.7 ± 10.0 Ma, 3.8 ± 0.6 Ma, and 17.0 ± 2.5 Ma, respectively. These ages are within the range typically observed for the respective meteorite types. GRV 98004 (H5) had an extremely short parent body-Earth transfer time of 0.052 ± 0.008 Ma. Its petrography and mineral chemistry are indistinguishable from other typical H5 chondrites. Only 3 other meteorites exist with similarly low CRE ages: Farmington (L5), Galim (LL6), and ALH 82100 (CM2). We show that several asteroids in Earth-crossing orbits, or in the main asteroid belt with orbits close to an ejection resonance, are spectrally matching candidates and may represent immediate precursor bodies of meteorites with CRE ages ≤0.1 Ma.

The meteorite Northwest Africa 773 (NWA 773) is a lunar sample with implications for the evolution of mafic magmas on the moon. A combination of key parameters including whole-rock oxygen isotopic composition, Fe/Mn ratios in mafic silicates, noble gas concentrations, a KREEP-like rare earth element pattern, and the presence of regolith agglutinate fragments indicate a lunar origin for NWA 773. Partial maskelynitization of feldspar and occasional twinning of pyroxene are attributed to shock deformation. Terrestrial weathering has caused fracturing and precipitation of Carich carbonates and sulfates in the fractures, but lunar minerals appear fresh and unoxidized. The meteorite is composed of two distinct lithologies: a two-pyroxene olivine gabbro with cumulate texture, and a polymict, fragmental regolith breccia. The olivine gabbro is dominated by cumulate olivine with pigeonite, augite, and interstitial plagioclase feldspar. The breccia consists of several types of clasts but is dominated by clasts from the gabbro and more FeO-rich derivatives. Variations in clast mineral assemblage and pyroxene Mg/(Mg + Fe) and Ti/(Ti + Cr) record an igneous Fe-enrichment trend that culminated in crystallization of fayalite + silica + hedenbergitebearing symplectites. The Fe-enrichment trend and cumulate textures observed in NWA 773 are similar to features of terrestrial ponded lava flows and shallow-level mafic intrusives, indicating that NWA 773 may be from a layered mafic intrusion or a thick, differentiated lava flow. NWA 773 and several other mafic lunar meteorites have LREE-enriched patters distinct from Apollo and Luna mare basalts, which tend to be LREE-depleted. This is somewhat surprising in light of remote sensing data that indicates that the Apollo and Luna missions sampled a portion of the moon that was enriched in incompatible heatproducing elements.

The cosmic ray exposure (CRE) ages of aubrites are among the longest of stone meteorites. New aubrites have been recovered in Antarctica, and these meteorites permit a substantial extension of the database on CRE ages, compositional characteristics, and regolith histories. We report He, Ne, and Ar isotopic abundances of nine aubrites and discuss the compositional data, the CRE ages, and regolith histories of this class of achondrites. A Ne three-isotope correlation reveals a solar-type ratio of 20Ne/22Ne = 12.1, which is distinct from the present solar wind composition and lower than most ratios observed on the lunar surface. For some aubrites, the cosmic ray-produced noble gas abundances include components produced on the surface of the parent object. The Kr isotopic systematics reveal significant neutron-capture-produced excesses in four aubrites, which is consistent with Sm and Gd isotopic anomalies previously documented in some aubrites. The nominal CRE ages confirm a non-uniform distribution of exposure times, but the evidence for a CRE age cluster appears doubtful. Six meteorites are regolith breccias with solar-type noble gases, and the observed neutron effects indicate a regolith history. ALH aubrites, which were recovered from the same location and are considered to represent a multiple fall, yield differing nominal CRE ages and, if paired, document distinct precompaction histories.

The trapped noble gases Ar, Kr and Xe in several achondrites were analysed. We chose separates of the lodranites Lodran and Graves Nunataks 95209 and bulk samples of the Tatahouine diogenite, Pasamonte eucrite, five aubrites and two angrites. Among these, Lodran, Tatahouine, Pasamonte and the aubrite Norton County have been reported to contain U-Xe, a noble gas component assumed to be the most primitive component in the solar system. U-Xe might have been incorporated into the early Earth. We found large concentrations of Xe in several separates of the Lodran lodranite, however, none of the measurements revealed U-Xe composition. The Xe composition of all achondrites can straightforwardly be explained with mixtures of trapped common Xe-Q, absorbed air and various amounts of fissiogenic and cosmogenic Xe. Reanalysis of literature data for Pasamonte, Angra dos Reis and some aubrites is consistent with Xe-Q as the trapped endmember component and contributions of fissiogenic Xe. The presence of Xe-Q in many primitive achondrites is in agreement with the formation of their parent bodies from originally chondritic precursor material. The Ar-Xe elemental composition of Lodran and the aubrites indicate subsolar composition, which is commonly found in E chondrites. This result supports a model of formation of the aubrites from E-chondritic precursor material.

The short-lived Hf-182-W-182-isotope system is an ideal clock to trace core formation and accretion processes of planets. Planetary accretion and metal/silicate fractionation chronologies are calculated relative to the chondritic Hf-182-W-182-isotope evolution. Here, we report new high-precision W-isotope data for the carbonaceous chondrite Allende that are much less radiogenic than previously reported and are in good agreement with published internal Hf-W chronometry of enstatite chondrites. If the W-isotope composition of terrestrial rocks, representing the bulk silicate Earth, is homogeneous and 2.24 epsilon(182W) units more radiogenic than that of the bulk Earth, metal/silicate differentiation of the Earth occurred very early. The new W-isotope data constrain the mean time of terrestrial core formation to 34 million years after the start of solar system accretion. Early terrestrial core formation implies rapid terrestrial accretion, thus permitting formation of the Moon by giant impact while Hf-182 was still alive. This could explain why lunar W-isotopes are more radiogenic than the terrestrial value. Copyright (C) 2002 Elsevier Science Ltd.

Mineralogy, major element compositions of minerals, and elemental and oxygen isotopic compositions of the whole rock attest to a lunar origin of the meteorite Northwest Africa 032 (NWA 032), an unbrecciated basalt found in October 1999. The rock consists predominantly of olivine, pyroxene and chromite phenocrysts, set in a crystalline groundmass of feldspar, pyroxene, ilmenite, troilite and trace metal. Whole-rock shock veins comprise a minor, but ubiquitous portion of the rock. Undulatory to mosaic extinction in olivine and pyroxene phenocrysts and micro-faults in groundmass and phenocrysts also are attributed to shock. Several geochemical signatures taken together indicate unambiguously that NWA 032 originated from the Moon. The most diagnostic criteria include whole-rock oxygen isotopic composition and ratios of Fe:Mn in the whole rock, olivine, and pyroxene. A lunar origin is documented further by the presence of Fe-metal, troilite, and ilmenite; zoning to extremely Fe-rich compositions in pyroxene; the ferrous oxidation state of all Fe in pyroxene; and the rare-earth element pattern with a well-defined negative europium anomaly. This rock is similar in major element chemistry to basalts from Apollo 12 and 15, but is enriched in light rare-earth elements and has an unusually high Th/Sm ratio. Some Apollo 14 basalts yield a closer match to NWA 032 in rare-earth element patterns, but have higher concentrations of Al2O3. Ar-Ar step release results are complex, but yield a whole-rock age of ca. 2.8 Ga, suggesting that NWA 032 was extruded at 2.8 Ga or earlier. This rock may be the youngest sample of mare basalt collected to date. Noble gas concentrations combined with previously collected radionuclide data indicate that the meteorite exposure history is distinct from currently recognized lunar meteorites. In short, the geochemical and petrographic features of NWA 032 are not matched by Apollo or Luna samples, nor by previously identified lunar meteorites, indicating that it originates from a previously unsampled mare deposit. Detailed assessment of petrographic features, olivine zoning, and thermodynamic modelling indicate a relatively simple cooling and crystallization history for NWA 032. Chromite-spinel, olivine, and pyroxene crystallized as phenocrysts while the magma cooled no faster than 2 °C/hr based on the polyhedral morphology of olivine. Comparison of olivine size with crystal growth rates and preserved Fe-Mg diffusion profiles in olivine phenocrysts suggest that olivine was immersed in the melt for no more than 40 days. Plumose textures in groundmass pyroxene, feldspar, and ilmenite, and Fe-rich rims on the phenocrysts formed during rapid crystallization (cooling rates ~ 20 to 60 °C/hr) after eruption.

— Several solar gas rich lunar soils and breccias have trapped 40Ar/36Ar ratios >10, although solar Ar is expected to yield a ratio of

Following the discovery of an apparent precompaction irradiation of a chondrule, we studied the isotopic abundances of noble gases He, Ne, and Ar in separated chondrule and matrix samples of eight ordinary chondrites. The chondrules show systematically larger concentrations of cosmogenic He, Ne, and with one exception, Ar when compared to the corresponding matrix samples. Different exposure times were calculated based on production rates, which take into account the abundances of relevant target elements in each chondrule and matrix sample. The 81Kr-Kr method was used for samples of Bjurbole to verify that different exposure times are not due to either a bias in production rates or to systematic losses of noble gases from matrix. This method self-corrects for variable shielding, is independent of calculated production rates, and insensitive to gas loss. The results show that differences in exposure ages are due to different precompaction exposures of chondrules, or components thereof, before final assembly of the meteorite. For the Sena chondrite we studied various chondrule and matrix constituents. For this meteorite we found chondrule preexposures relative to the matrix material, with magnetic chondrules showing the largest effect.

— We derived the cosmic-ray and solar particle exposure history for the two lunar meteorites Elephant Moraine (EET) 96008 and Dar al Gani (DaG) 262 on the basis of the noble gas isotopic abundances including the radionuclide 81Kr. For EET 96008, we propose a model for the exposure to cosmic rays and solar particles in three stages on the Moon: an early stage ∼500 Ma ago, lasting less than 9 Ma at a shallow shielding depth of 20 g/cm2, followed by a stage when the material was buried, without exposure, until it was exposed in a recent stage. This recent stage, at a shielding depth in a range of 200–600 g/cm2, lasted for ∼26 Ma until ejection. This model is essentially the same as that previously found for lunar meteorite EET 87521; thus, pairing of the two Elephant Moraine lunar meteorites that were recovered on the same icefield in Antarctica is confirmed by our data. The cosmic-ray-produced isotopes, the trapped solar and lunar atmospheric noble gases, as well as the radionuclide 81Kr observed for the DaG 262 lunar meteorite are consistent with a one-stage lunar exposure history. The average burial depth of the Dar al Gani material before ejection was within a range of 50–80 g/cm2. The exposure to cosmic rays at this depth lasted 500–1000 Ma. This long residence time for Dar al Gani at relatively shallow depth explains the high concentrations of implanted solar noble gases.

— Acapulcoites and lodranites are believed to originate on a common parent body and to represent some of the earliest events in the differentiation of the chondritic asteroids. We have conducted isotopic studies of the noble gases He, Ne, Ar, Kr, and Xe, and determinations of the concentrations of the major elements and of the radionuclides 10Be, 26Al, and 36Cl in an attempt to constrain the cosmic-ray exposure history of two members of the acapulcoite-lodranite clan recovered in Antarctica: Frontier Mountain (FRO) 95029 and Graves Nunataks (GRA) 95209. From cosmic-ray-produced 3He, 21Ne, and 38Ar and appropriate production rates, we derive parent-body breakup times of 4.59 ± 0.60 and 6.82 ± 0.60 Ma for FOR 95029 and GRA 95209, respectively. These times are consistent with those obtained from the pairs 10Be-21Ne and 26Al-21Ne; whereas the times inferred from the pair 36Cl-36Ar are slightly longer, perhaps because the 36Cl activities decreased as a result of decay on Earth. Terrestrial ages up to ∼50 ka for the two meteorites are consistent with the measured 36Cl activities of the metal phases. All acapulcoites and lodranites dated until now show cosmic-ray exposure ages in the range of 4–10 Ma. This is the same range as that found for the major exposure age cluster of the H chondrites. As a common parent body is improbable on the basis of the O-isotopic systematics, a common set of impactors might have affected the asteroid belt 4–10 Ma ago.

— We performed a comprehensive study of the noble gas isotopic abundances, radionuclide activities, and mineralogical and chemical composition of two mesosiderites and two iron meteorites. For the mesosiderites Dong Ujimqin Qi and Weiyuan, the silicate and the metal phases were studied. The anomalous ataxite Rafruti is not chemically related to any other meteorite class, whereas Ningbo is a type IVA octahedrite. The mineralogy and major and trace element abundances of the silicate phases of Dong Ujimqin Qi and Weiyuan are similar to those of other mesosiderites and distinct from those of the howardites. The cosmic-ray exposure history was studied based on the concentrations of the cosmogenic noble gas nuclei and radionuclide activities. For the iron meteorites, cosmic-ray exposure ages were calculated from the pairs 10Be-21Ne, 26Al-21Ne, and 36Cl-36Ar. Rafruti yields the youngest exposure age of all ataxites (6.8 ± 1.7 Ma), whereas that of Ningbo with 107 ± 15 Ma falls within the range observed for the other octahedrites. The parent body break-up times of the mesosiderites Dong Ujimqin Qi and Weiyuan are 252 ± 50 and 25.9 ± 5.0 Ma, respectively. We find no evidence for a common break-up event for the mesosiderites and the howardites.

We studied the cosmic-ray records of the H6 chondrite ALH76008 in a bulk sample, in a chondrule fragment, and in matrix material. The matrix was separated into olivine/pyroxene, plagioclase, and metal concentrates. For all samples He, Ne, and Ar isotopic measurements were performed. The cosmic-ray exposure age of the bulk chondrite is 1.72 ± 0.11 Ma, whereas the 3He, 21Ne, and 38Ar ages of the chondrule exceed those of bulk material by 31%, 67%, and 55%, respectively. The radiation environment in the early solar system is ill defined, but for current production rates this translates into a precompaction exposure time of 0.90 Ma. Furthermore, the plagioclase (mainly anorthite) concentrate, representing a few percent of the total meteorite, contains solar-type noble gases that reveal differential irradiation of ALH76008 components. We observe a trapped ratio 20Ne/22Ne = 12.3 ± 0.3, a value that is between those of solar wind and solar energetic particles. This is the first clear identification of differential irradiation conditions between a chondrule and the bulk chondrite; the short exposure age may favor the resolution of differential exposure histories.

— We report the noble gas isotopic abundances of five dimict breccias and one cataclastic anorthosite that were collected at the Apollo 16 landing site. Orbital and surface photographs indicate that rays from South Ray crater, an almost 1 km wide young crater in the Cayley plains, extend several kilometers from their source into the area that was sampled by the Apollo 16 mission. Previous studies have shown that South Ray crater formed 2 Ma ago and that a large number of rocks might originate from this cratering event. On the basis of cosmic-ray produced nuclei, we find that the six rocks investigated in this work yield the same lunar surface exposure age. Using literature data, we recalculate the exposure ages of additional 16 rocks with suspected South Ray crater origin and obtain an average exposure age of 2.01 ± 0.10 Ma. In particular, all nine dimict breccias (a type of rock essentially restricted to the Apollo 16 area consisting of anorthosite and breccia phases) dated until now yield an average ejection age of 2.06 ± 0.17 Ma. We conclude that they must originate from the Cayley formation or from bedrock underlying the Cayley plain. We determined the gas retention ages for the dimict breccias based on the 40K-40Ar and U,Th-136Xe dating methods: rock 64425 yields a 40K-40Ar age of 3.96 Ga and rock 61016 a U,Th-136Xe age of 3.97 Ga. These results, together with 39Ar-40Ar ages obtained by other workers for rocks 64535 (3.98 Ga) and 64536 (3.97 Ga), show that the dimict breccias formed 3.97 Ga ago.

Noble gas isotopic abundances of ten lodranites (EET84302, FRO90011, Gibson, LEW86220, LEW88280, Lodran, MAC88177, QUE93148, Y74357, Y791491) and four acapulcoites (Acapulco, ALH81187, ALH81261, ALH84190), as well as major, minor, and trace element compositions of six lodranites (EET84302, Gibson, LEW88280, Lodran, MAC88177, Y791491), are reported. Because existing empirical production rate models for cosmic-ray-produced nuclides in achondrites could not account for the effects of bulk chemical composition and for the unique shielding conditions in lodranites and acapulcoites, we modeled the production rates of cosmogenic nuclides in lodranites and acapulcoites by galactic and solar cosmic rays using a purely physical model. All lodranites and acapulcoites are relatively small meteorites having preatmospheric radii ≤ 200 mm, one-half of them even ≤75 mm. Evidence was found for solar-cosmic ray produced nuclides in the acapulcoites ALH77081, ALH81187, ALH81261, and ALH84190. The derived cosmic-ray exposure ages of all lodranites (with the exception of QUE93148 with 15 Ma) and all acapulcoites cluster around 6 Ma, suggesting, supported by the similar abundances of cosmogenic nuclides, similar shielding conditions, and similar chemical compositions, that they all originate from one ejection event from the same parent body. Within error limits identical abundances of cosmogenic nuclides, identical shielding conditions, and identical cosmic-ray exposure ages support pairing between ALH77081 and ALH81261, and ALH81187 and ALH84190.

We present He, Ne, and Ar data on stepwise heating experiments for the CM-2 chondrite LEW90500 and on noble gas isotopic abundances of the anomalous CK chondrite Maralinga. In LEW90500 we observe at least 0.20 × 10−8 cm3STP/g Ne-E probably originating from the decay of presolar 22Na. Planetary He is characterized by 4He/3He = 6500. For planetary-type trapped noble gases we obtain 20Netr = 13.4 × 10−8 cm3STP/g and (36Ar/20Ne)tr = 5.6. The cosmic-ray exposure age, based on 21Nec is 0.24 Ma. We review the literature data of the other CM-2 chondrites and find a Ne-E component in most of them; the largest concentration is observed in Mighei (0.53 × 10−8 cm3STP/g). The exposure age distribution of the CM-2 chondrites confirms previous studies that report generally young ages (

— We report the elemental and isotopic composition of the noble gases as well as the chemical abundances in pyroxene, maskelynite/mesostasis glass, and bulk material of Shergotty and of bulk samples from Chassigny and Yamato 793605. The 40K-40Ar isochron for the Shergotty minerals yields a gas retention age of 196 Ma, which is, within errors, in agreement with previously determined Rb-Sr internal isochron ages. Argon that was trapped at this time has a 40Ar/36Ar ratio of 1100. For Chassigny and Y-793605, we obtain trapped 40Ar/36Ar ratios of 1380 and 950, respectively. Using these results and literature data, we show that the three shergottites, Shergotty, Zagami, and QUE 94001; the lherzolites ALH 77005, LEW 88516, and Y-793605; as well as Chassigny and ALH 84001 contain a mixture of Martian mantle and atmospheric Ar; whereas, the trapped 40Ar/36Ar ratio of the nakhlites, Nakhla, Lafayette, and Governador Valadares cannot be determined with the present data. We show that Martian atmospheric trapped Ar in Martian meteorites is correlated with the shock pressure that they experienced. Hence, we conclude that the Martian atmospheric gases were introduced by shock into the meteoritic material. For the Shergotty minerals, we obtain 3He-, 21Ne-, and 38Ar-based cosmic-ray exposure ages of 3.0 Ma, and for the lherzolite Y-793605, 4.0 Ma, which confirms our earlier conclusion that the lherzolites were ejected from Mars ∼1 Ma before the shergottites. Chassigny yields the previously known ejection age of 11.6 Ma.

— We measured the noble gas isotopic abundances in lunar meteorite QUE 94269 and in bulk-, glass-, and crystal-phases of lunar meteorite QUE 94281. Our results confirm that QUE 94269 originated from the same meteorite fall as QUE 93069: both specimens yield the same signature of solar-particle irradiation and also the cosmogenic noble gases are in agreement within their uncertainities. Queen Alexandra Range 93069/94269 was exposed to cosmic rays in the lunar regolith for ∼1000 Ma, and it trapped 3.5 × 10−4 cm3STP/g solar 36Ar, the other solar noble gases being present in proportions typical for the solar-particle irradiation. The bulk material of QUE 94281 contains about three times less cosmogenic and trapped noble gases than QUE 93069/94269 and the lunar regolith residence time corresponds to 400 ± 60 Ma. We show that in lunar meteorites the trapped solar 20Ne/22Ne ratio is correlated with the trapped ratio 40Ar/36Ar, that is, trapped 20Ne/22Ne may also serve as an antiquity indicator. The upper limits of the breccia compaction ages, as derived from the trapped ratio 40Ar/36Ar for QUE 93069/94269 and QUE 94281 are ∼400 Ma and 800 Ma, respectively. We found very different regolith histories for the glass phase and the crystals separated from QUE 94281. The glass phase contains much less cosmogenic and solar noble gases than the crystals, in contrast to the glasses of lunar meteorite EET 87521, that were enriched in noble gases relative to the crystalline material. The QUE 94281 phases yield a 40K-40Ar gas retention age of 3770 Ma, which is in the range of that for lunar mare rocks.

We present a study of the noble gas isotopic abundances in two achondrites, Divnoe and the Asuka 881371 angrite. For Divnoe, we also performed chemical analyses of the major elements and of some minor and trace elements that are relevant for the comparison with other meteorite types and for the interpretation of the noble gas data. Based on the cosmic-ray produced noble gases, an exposure age of 5.4 ± 0.7 Ma for Asuka 881371 was obtained. This ejection time from the parent asteroid differs from those of the other three angrites—Angra dos Reis (55.5 Ma), LEW 86010 (17.6 Ma), and LEW 87051 (≥0.2 Ma). Whereas the U,Th- 4 He, and K- 40 Ar gas retention ages of Asuka 881371 are 3750 ± 1000 Ma and 3910 ± 500 Ma, respectively, we derive for the 244 Pu- 136 Xe system, a formation age of 4533 ± 40 Ma, which is contemporaneous with that of the other angrites Angra dos Reis and LEW 86010. For Divnoe the abundance patterns of the major lithophile, siderophile, refractory, and volatile elements, the isotopic abundance pattern for primordial trapped Xe, and the oxygen isotopes indicate that this unique meteorite is related to the brachinite achondrites. Assuming no pre-exposure to cosmic rays on the parent body, Divnoe's asteroid ejection event occurred 17.2 ± 2.3 Ma ago.

— We investigated the characteristics and history of lunar meteorites Queen Alexandra Range 93069, Yamato 793169 and Asuka 881757 based on the abundances of all stable noble gas isotopes, the concentrations of the radionuclides 10Be, 26Al, 36Cl, and 81Kr, and the abundances of Mg, Al, K, Ca, Fe, Cl, Sr, Y, Zr, Ba, and La. Based on the solar wind and cosmic-ray irradiations, QUE 93069 is the most mature lunar meteorite studied up to now. The 40Ar/36Ar ratio of the trapped component is 1.87 ± 0.16. This ratio corresponds to a time when the material was exposed to solar and lunar atmospheric volatiles ∼400 Ma ago. On the other hand, Yamato 793169 and Asuka 881757 contain very little or no solar noble gases, which indicates that these materials resided in the top layer of the lunar regolith only briefly or not at all. For all lunar meteorites, we observe a positive correlation of the concentrations of cosmic-ray produced with trapped solar noble gases. The duration of lunar regolith residence for the lunar meteorites was calculated based on cosmic-ray produced 21Ne, 38Ar, 78Kr, 83Kr, and 126Xe and appropriate production rates that were derived based on the target element abundances and the shielding indicator 131Xe/126Xe. For QUE 93069, Yamato 793169, and Asuka 881757, we obtained 1000 ± 400 Ma, 50 ± 10 Ma, and

— Glass-rich separates were prepared from a sample of the basaltic lunar meteorite EET87521 rich in dark glass. Noble gas isotopic abundances and 26Al and 10Be activities were measured to find out whether shock effects associated with lunar launch helped to assemble these phases. Similar 10Be and 26Al activities indicate that all materials in EET87521 had a common exposure history in the last few million years before launch. However, the glass contains much higher concentrations of trapped gases and records a much longer cosmic-ray exposure, 100 Ma–150 Ma, in the lunar regolith than does the bulk sample. The different histories show that the glass existed long before the ejection of EET87521. The trapped 40Ar/36Ar ratio of 1.6 ± 0.1 implies that the lunar exposure that produced most of the stable cosmogenic noble gases began 500 Ma ago. Cosmogenic and trapped noble gas components correlate strongly in various temperature-release fractions and phases of EET87521, which is probably because the glass contains most of the gas. The trapped solar ratios, 20Ne/22Ne = 12.68 ± 0.20 and 36Ar/38Ar = 5.24 ± 0.05 can be understood as resulting from a mixture consisting of ∼60% solar wind and 40% solar energetic particles (SEP). All EET87521 phases show a 40K-40Ar gas retention age of ∼3300 Ma, which is in the range of typical lunar mare basalts.

We determined the cosmic-ray produced noble gas abundances in eight diogenites, four eucrites, and four howardites. Using these and additional noble gas and chemical data from the literature, composition and shielding dependent production rates of achondrites for 3He, 21Ne, 38Ar, 78Kr, 83Kr, and126Xe were derived based on 81KrKr exposure ages. The cosmogenic ratio 22Ne/21Ne is found to be a valid shielding indicator for all howardites, eucrites, and diogenites (HEDs). This ratio correlates with other shielding dependent ratios, such as 78Kr/83Kr, 80Kr/83Kr, 124Xe/131Xe, 126Xe/131Xe, and 128Xe/131Xe. We show that strong correlations for these ratios also exist for basaltic lunar rocks. The new production rates were used for the calculation of exposure ages for all HEDs with known noble gas abundances. Two major exposure age clusters at 21 Ma and 38 Ma are observed in all three classes. We find that five asteroid break-up events, characterized by exposure ages 6 ± 1 Ma, 12 ± 2 Ma, 21 ± 4 Ma, 38 ± 8 Ma, and 73 ± 3 Ma produced all diogenites, fifteen out of seventeen howardites, and twenty-eight out of thirty-nine eucrites. We conclude that asteroidal or cometary impact events at such times on one or several parent bodies are responsible for the ejection of eucrites, howardites, and diogenites. Probable parent bodies are multiple 4 Vesta-derived kilometer-sized objects of basaltic achondritic composition reaching the 3:1 resonance region, a proposed source area for meteorites. The direct ejection from Vesta and capture by Earth of basaltic meteorites has been shown to be dynamically difficult. In such a scenario large events 38 Ma and 21 Ma ago are required, liberating simultaneously material representing Vesta's surface (eucrites, howardites) and interior regions (diogenites).

The 244Pu-fission-136Xe retention ages of howardites, eucrites, and diogenites (HEDs) show that these meteorites have retained Xe since they were formed about 4500 Ma ago. For the Garland diogenite and the Millbillillie eucrite, we obtain fission Xe ages of 4525 ± 40 Ma and 4486 ± 40 Ma, respectively. If Xe isotope data reported by other workers are also considered, we conclude that the monomict equilibrated eucrites Camel Donga, Juvinas, and Millbillillie formed about 40 Ma later than Pasamonte, a polymict unequilibrated eucrite. Stannern, a monomict equilibrated brecciated eucrite, yields a 244Pu-136Xe age of 4442 Ma. The 40K-40Ar retention ages fall, for most HEDs, into the 1000–4000 Ma age range, indicating that 40Ar is generally not well retained. The good retentivity for Xe of HEDs allows us to study primordial trapped Xe in these meteorites. Except for Shalka, in which other authors found Kr and Xe from terrestrial atmospheric contamination only, we present for the first time Kr and Xe isotopic data for diogenites. We studied Ellemeet, Garland, Ibbenbuhren, Shalka, and Tatahouine. We show that Tatahouine contains two types of trapped Xe: a terrestrial contamination acquired by an irreversible adsorption process and released at pyrolysis temperatures up to 800 °C, and indigenous primordial Xe released primarily between 800 °C and 1200 °C. The isotopic composition of this primordial Xe is identical to that proposed earlier to be present in primitive achondrites and termed U-Xe or “primitive” Xe, but it has not been directly observed in achondrites until now. This type of primitive Xe is important for understanding the evolution of other Xe reservoirs in the Solar System. Terrestrial atmospheric Xe (corrected for fission Xe and radiogenic Xe from outgassing of the Earth) is related to it by a mass dependent fractionation favoring the heavier Xe isotopes. This primitive Xe is isotopically very similar to solar Xe except for 134Xe and 136Xe. Solar Xe appears to contain an enrichment of unknown origin for these isotopes relative to the primitive Xe.

We report the noble gas concentrations and the Al-26, Be-10, Cl-36, and Ca-41 activities of the Antarctic lunar meteorite Elephant Moraine 87521. Although the actual exposure history of the meteorite may have been more complex, the following model history accounts satisfactorily for the cosmogenic nuclide data: A first stage of lunar irradiation for about 1 Ma at a depth of 1-5 g/sq cm followed, not necessarily directly, by a second one for 26 Ma at about 565 g/sq cm; launch from the moon less than 0.1 Ma ago; and arrival on earth 15-50 ka ago. The small concentration of trapped gases shows that except for some material that may have been introduced at the moment of launch, EET 87521 spent less than 1 Ma at a lunar depth less than 1 g/sq cm. EET 87521 has a K/Ar age in the range 3.0-3.4 Ga, which is typical for lunar mare basalts.

Lunar anorthositic breccias 60018 and 65315 contain a trapped Xe component with isotope ratios similar to those in terrestrial atmospheric Xe. We analyzed all five noble gases in eight grain size fractions of 60018 and in several bulk samples of 65315 in order to characterize the nature of the trapped components. Trapped gas abundances in 60018 are 100 to 1000 times lower than in a typical regolith breccia; they are grain size anticorrelated for grain sizes < 30 μm. In 65315, trapped He, Ne, and Ar concentrations are among the lowest ever observed for lunar material. Except for Xe, the isotopic abundances of the trapped components in both rocks are consistent with solar wind composition. Because of the uncertain results as to the origin of the terrestrial-like Xe component, we crushed samples of 60018 and 65315 in atmospheres spiked with 86Kr and 129Xe. These experiments showed unequivocally that anorthositic samples can be contaminated by Kr and Xe, and maybe also by Ar, from the ambient atmosphere. At least 75% of the acquired terrestrial and spike gases are released only at temperatures above 600°C. Krypton and xenon concentrations are grain-size anticorrelated, indicating surface adherence of the gas atoms. Furthermore, the amount of gas in a sample is approximately proportional to the partial pressure of the gas to which the sample was exposed, as described by Henry's law. Xenon uptake is about one order of magnitude more effective than Kr uptake, and activation energies, measured at room temperature, are in the range of 10–20 kJ/mol. Both characteristics are typical for ordinary physical adsorption. However, the high extraction temperatures show that somehow the gas atoms get fixed, either by strong chemisorptive bonding with activation energies around 200 kJ/mol, or by getting trapped beneath the surface. Therefore, we use the term “irreversible adsorption” for the phenomenon. Fixation is likely to take place during crushing, when mechanical, thermal, and maybe electromagnetic energy is supplied, although the air contamination of an uncrushed 65315 sample cannot be explained in this way. Irreversible adsorption of terrestrial Kr and Xe has been observed for several lunar anorthosites with low solar wind content, but also for some meteoritic samples, in particular diogenites, which are composed mainly of pyroxene. A similar process may have been responsible for the incorporation of nonterrestrial noble gas components into extraterrestrial material, e.g., the planetary trapped gases in meteorites or the surface-correlated components of 129Xe and fission-type Xe in some lunar breccias. Furthermore, other volatile elements might be affected by irreversible adsorption.

The original mass (15915 g) of the Twannberg IIG (low Ni-, high P) iron was found in 1984. Five additional masses (12 to 2488 g) were recovered between 2000 and 2007 in the area. The different masses show identical mineralogy consisting of kamacite single crystals with inclusions of three types of schreibersite crystals: cm-sized skeletal (10.5% Ni), lamellar (17.2% Ni), and 1-3 x 10 μm-sized microprismatic (23.9% Ni). Masses I and II were compared in detail and have virtually identical microstructure, hardness, chemical composition, cosmic-ray exposure (CRE) ages, and 10Be and 26Al activities. Bulk concentrations of 5.2% Ni and 2.0% P were calculated. The preatmospheric mass is estimated to have been at least 11,000 kg. The average CRE age for the different Twannberg samples is 230 ± 50 Ma. Detrital terrestrial mineral grains in the oxide rinds of the three larger masses indicate that they oxidized while they were incorporated in a glacial till deposited by the Rhone glacier during the last glaciation (Wrm). The find location of mass I is located at the limit of glaciation where the meteorite may have deposited after transport by the glacier over considerable distance. All evidence indicates pairing of the six masses, which may be part of a larger shower as is indicated by the large inferred pre-atmospheric mass.

The recently discovered Jiddat al Harasis (JaH) 073 strewn field is the largest found so far in the Sultanate of Oman, covering an area of 19 6 km. The 3463 single stones collected range in weight from 52.2 kg down to

Noble gas isotopes, radionuclides, and chemical abundances were studied in the lunar meteorites MAC88104 and MAC88105 collected in the MacAlpine Hills area of Antarctica. The concentrations of the noble gas isotopes and the radionuclide activities in the two meteorites are essentially identical, proving that the two meteorites are paired. From 40K-40Ar dating we obtain a gas retention age of 3550 ± 400 Ma, typical for lunar surface material. Probably before breccia compaction the MAC88104/5 material resided for 630 ± 200 Ma at an average shielding depth of 85 g cm 2 , that is, about 50 cm below the lunar surface in the lunar regolith, as judged from the concentration of cosmic-ray produced Kr and Xe isotopes. Although this duration of lunar regolith residence is relatively long, MAC88104/5 represent immature regolith material: the concentration of solar wind implanted noble gases are two orders of magnitude lower than those in mature lunar soil. The reason for that might be the relatively high average shielding. The 40 Ar 36Ar ratio of the trapped component is 5.7 ± 1.0, indicating an intermediate antiquity of the material; we estimate that the solar wind and lunar atmospheric particles were implanted about 2000 Ma ago. The radionuclide activities allow us to derive the exposure history of the MAC88104/5 material. The duration of the Moon-Earth transfer was ≦0.24 Ma. Production of the radionuclides on the lunar surface immediately before ejection is possible, but duration and shielding depth for such an exposure cannot be determined from our data. We obtain a terrestrial age of 0.1 ≦ tterr ≦ 0.6 Ma and an ejection time of MAC88104/5 from the Moon of 0.1 ≦ tejection ≦ 0.8 Ma. The exposure histories of the lunar meteorites discussed in this work indicate that at least two impact events are required for their ejection from the Moon. Our first noble gas results for lunar meteorite Yamato-793274 show that it represents mature lunar regolith material with relatively high concentrations of solar wind implanted noble gases and a duration of several hundred million years of exposure to cosmic rays.

We have studied noble gas isotopic abundances in the two angrites LEW86010 and LEW87051. Many characteristics of LEW86010 are similar to those observed for the basaltic achondrite Angra dos Reis, until recently the only known angrite. Fission Xe in LEW86010 originates almost entirely from 244Pu fission. We calculate an atomic ratio 244 Pu 150 Nd = 1.36 × 10 −3 that corresponds to a fission Xe retention age 19 ± 40 Ma younger than that of Angra dos Reis. Thus, LEW86010 formed contemporaneously with Angra dos Reis for which previous analyses yielded a formation age of 4550 Ma. The U/ Th-4He age (3700 Ma) of LEW86010 is higher than the K-40Ar gas retention age, a feature observed earlier for Angra dos Reis. LEW87051 shows the lowest nominal U/Th-4He gas retention age (4 Ma) ever observed for a stone meteorite. The cosmic-ray exposure histories are very different for the three angrites: for LEW86010 and LEW87051 we calculate 17.6 ± 1.0 Ma and ≧ 0.2 Ma, respectively, compared to a previously reported exposure age of 55.5 Ma for Angra dos Reis. For the radionuclide 81Kr we measured an activity of 0.012 dpm/kg in LEW86010 and derive a terrestrial age of 420 000 ± 100 000 years.

The chemical composition of the chondritic breccia Allan Hills 85085 does not match that of any known group of chondrites. In addition, this meteorite contains extremely fine-grained fragments and small chondrule-like inclusions. We investigated the noble gas isotopic abundances in bulk samples, in a fine-grained silicate fraction, and in a coarse-grained fraction containing the metal phase. Solar gases are present in the fine-grained silicates and indicate processing of the ALH85085 material in an asteroidal regolith. He and Ne are enriched in a < 40 μm grain size fraction indicating surface implantation of solar particles. The solar noble gas component is characterized by an elemental abundance pattern and isotopic ratios typical for lunar and asteroidal regolith material: 4He/36Ar= 469, 20Ne/36Ar = 4.2, 4He/3He= 2300 ± 600, 20Ne/22Ne= 12.5 ± 0.4. The major noble gas component in the bulk and coarse-grained fractions are planetary type trapped gases. Abundances and isotopic composition are similar to those in type-2 and -3 chondrites. In some respects ALH85085 resembles another unique chondrite, Kakangari, but it differs in its FeNi content that is almost twice as high as in Kakangari, and in other characteristics. Both, the cosmic-ray exposure age and the K—40Ar gas retention age, are relatively low: The travel time of ALH85085 as a small object in space was 1.7 ± 0.8Ma and a fraction of40Ar was lost as indicated by the40K—40Ar retention age of 2900 ± 300Ma.

— Richfield is a moderately shocked (shock stage S4) LL3.7 genomict breccia find consisting mainly of light-colored recrystallized clasts and dark clasts exhibiting significant silicate darkening; a few impact-melt-rock clasts and LL5 chondrite clasts also occur. The cosmic-ray exposure age of 14.5 Ma is indistinguishable from the main exposure peak for LL chondrites (15 Ma). Although the exposure ages indicate little He loss, the gas-retention ages indicate high gas losses that must have occurred prior to or during ejection from the LL parent body.

The lunar meteorite Sayh al Uhaymir 169 consists of an impact melt breccia extremely enriched with potassium, rare earth elements, and phosphorus [thorium, 32.7 parts per million (ppm); uranium, 8.6 ppm; potassium oxide, 0.54 weight percent], and adherent regolith. The isotope systematics of the meteorite record four lunar impact events at 3909 +/- 13 million years ago (Ma), approximately 2800 Ma, approximately 200 Ma, and0.34 Ma, and collision with Earth sometime after 9.7 +/- 1.3 thousand years ago. With these data, we can link the impact-melt breccia to Imbrium and pinpoint the source region of the meteorite to the Lalande impact crater.

Several recent papers have applied correlation analysis to climate-related time series in the hope of finding evidence for causal relationships. For a critical discussion of correlations between solar variability, cosmic rays, and cloud cover, see Laut [2003]. A prominent new example is a paper by Shaviv and Veizer [2003], which claims that fluctuations in cosmic ray flux reaching the Earth can explain 66% of the temperature variance over the past 520 m.y.,and that the sensitivity of climate to a doubling of CO2 is less than previously estimated.

We performed a comprehensive study of the noble gas isotopic abundances in thirty-six chondrites including twenty-seven chondrites recovered in China. The large data base allows us to recognize some new characteristics of the nuclear record in chondritic matter. The comparison of the trapped noble gas release pattern for ordinary and carbonaceous chondrites shows that the planetary trapped noble gases in ordinary chondrites are released mainly above 1200°C whereas ≥85% of these gases in carbonaceous chondrites are degassed at ≥ 200°C. There exists a clear correlation of the fraction of trapped Xe released at > 1200°C and petrologic type of chondrites. It thus appears that the carrier phases of the trapped noble gases in ordinary and in carbonaceous chondrites may not be the same. The Ngawi LL3 chondrite is solar gas rich. The solar gases in meteorites and lunar surface material are mixtures of solar wind (SW) and solar energetic particles (SEP). We show that the variations of the 3 He 4 He and 20 Ne 22 Ne ratios for solar gas-rich meteorites and lunar surface material could be either due to preferential diffusive losses of the lighter isotopes of He and Ne or due to a change of the SW/SEP flux ratio with time. Furthermore, we demonstrate that the 81Kr concentration is a function of the shielding depth of a sample within the meteoroid. Deviations from this depth dependency curve are observed for Jilin (H5), Lishui (L5), Suizhou (L6), and Dongtai (LL6). A complex exposure history for Jilin is thus confirmed and is possible for the other three chondrites. Cosmic-ray exposure ages are calculated based on six different nuclides—3He, 21Ne, 38Ar, 83Kr, 126Xe, and 81Kr-Kr. In most cases good agreement is observed for the ages derived from the different methods. Quality classes are assigned to the exposure ages, and the age distributions are discussed. In some meteorites we observe effects induced by secondary cosmicray-produced neutrons. Epithermal neutron fluxes, Jn(30–300 eV), and fast neutron fluxes, Jn(>5 MeV), are derived based on the reactions 79Br(n, γβ)80Kr and 24Mg(n, α)21Ne, respectively; and preatmospheric masses of the meteoroids are estimated. We show that the ratio J n (30–300 eV) J n (> 5 MeV) increases with increasing preatmospheric mass. We introduce a 3He exposure age/21Ne exposure age vs. 4He gas retention age/40Ar gas retention age diagram that is a powerful tool for distinguishing different thermal histories of meteoroids. Finally, in some chondrites we observe Xe produced by 244Pu fission and calculate the time span between fission-Xe retention in these chondrites and that of the Angra dos Reis achondrite. We find that the ordinary chondrites started to retain fission Xe 48 ± 30 Ma earlier than Angra dos Reis; we do not observe systematic differences between H, L, and LL or type 5 and 6 chondrites with respect to the time of fission Xe retention.

In our analysis [Rahmstorf et al., 2004], we arrived at two main conclusions: the data of Shaviv and Veizer [2003] do not show a significant correlation of cosmic ray flux (CRF) and climate, and the authors' estimate of climate sensitivity to CO2 based on a simple regression analysis is questionable. After careful consideration of Shaviv and Veizer's comment, we want to uphold and reaffirm these conclusions. Concerning the question of correlation, we pointed out that a correlation arose only after several adjustments to the data, including shifting one of the four CRF peaks and stretching the time scale. To calculate statistical significance, we first need to compute the number of independent data points in the CRF and temperature curves being correlated, accounting for their autocorrelation. A standard estimate [Quenouille, 1952] of the number of effective data points is NEFF ≅ N1+2∑k=1Nr1(k)r2(k) where N is the total number of data points and r1, r2 are the autocorrelations of the two series. For the curves of Shaviv and Veizer [2003], the result is NEFF = 4.8. This is consistent with the fact that these are smooth curves with four humps, and with the fact that for CRF the position of the four peaks is determined by four spiral arm crossings or four meteorite clusters, respectively; that is, by four independent data points. The number of points that enter the calculation of statistical significance of a linear correlation is (NEFF− 2), since any curves based on only two points show perfect correlation; at least three independent points are needed for a meaningful result.

We present a comprehensive study of the elemental and isotopic abundances of the noble gases He, Ne, Ar, Kr, and Xe in the meteorite Allan Hills A81005 from the Moon. In addition to a bulk sample five grain size fractions were analyzed. Chemical abundances relevant for the interpretation of the cosmic-ray-produced noble gases were determined and indicate that the grain size fractions are chemically uniform. Except for the fact that the trapped noble gas concentrations appear to be grain size correlated, the isotopic and elemental pattern of the trapped solar wind noble gases in A81005 are very similar to those observed in lunar soils and breccias. The A81005 material resided during (580 ± 180) m.y. in the nuclear active zone of the lunar regolith at an average shielding depth of about 40 g/cm2. From literature data we conclude that the Moon-Earth transit time lasted less than a few million years. Finally, A81005 was captured by the Earth more than 140,000 years ago as obtained from the abundance of cosmic-ray-produced81Kr.

A comprehensive study of the cosmic-ray exposure history of five ordinary chondrites from China was carried out using measurements of the noble gas isotopic abundances and 10 Be concentrations. The following average cosmic-ray exposure ages, based on cosmogenic 21 Ne and on 81 Kr Kr dating were obtained: Zhaodong (L4) — 15.7 ± 3.0 m.y., Nan Yang Pao (L6) — 48 ± 10.0 m.y., Guangrao (L6) — 16.8 ± 3.5 m.y., and Lunan (H6) — 26.7 ± 5.0 m.y. The H5 chondrite Zaoyang was exposed for only 0.90 ± 0.12 m.y. to galactic cosmic rays as calculated from the 10 Be activity and from the low amounts of cosmic-ray-produced noble gases. The Zhaodong chondrite contains large amounts of 80 Kr and 82 Kr produced by neutron capture of bromine. From the high slowing down density for neutrons we derive a preatmospheric mass of more than 1800 kg for this meteorite.

The isotope abundances of He, Ne, Ar, Kr, and Xe, including ^Kr, the oxygen isotopic composition, and the concentrations of Na, K, Sc, Ti, Cr, Fe, Co, Y, Zr, La, Sm, Eu, Hf, Ta, and W were determined for the lunar meteorite Yamato-86032. Based on the radionuclide ^Kr we obtain a terrestrial age of 72000±30000 years, whereas the cosmic-ray exposure age is 10.6±0.6 Ma assuming exposure of the meteorite as a small object in space. Exposure to cosmic rays occurred at shallow shielding of about 40g/cm^2. The K-Ar gas retention ages of two separate splits are 3680±300 Ma and 3810±400 Ma, respectively. All ages agree with those for the lunar meteorites Y-82192 and Y-82193 recovered in the same area on the antarctic ice. The small amounts of trapped solar wind noble gases indicate that the Y-86032 material was exposed only briefly, some grains perhaps not at all, to the solar wind. The concentrations are similar to those of the Yamato-82 lunar meteorites. The oxygen isotopic composition is within the range of that for lunar rocks. The chemical composition of the samples from Y-86032,Y-82192,and Y-82193 is uniform for most major elements but not for all minor and trace elements, probably due to inhomogeneity of the source material. From the fact that the history of Y-86032 is the same as that of Y-82192/3 we conclude that these three rocks are pieces of the same meteorite fall.

We analyzed the isotope abundances of He, Ne, Ar, Kr, and Xe in bulk samples and grain size separates of the lunar meteorites Yamato-82192 and -82193 collected in Antarctica. The history of exposure to cosmic rays and the terrestrial age is the same for both meteorites, confirming earlier suggestions that the two stones are fragments of the same meteorite fall. The terrestrial ages were determined using the radioisotope81Kr in combination with stable cosmic-ray-produced noble gases. For Y-82192 and Y-82193 we obtain 83,000 ± 35,000y and 75,000 ± 30,000y, respectively. The Moon-Earth transit time lasted about 8 ± 3My. The upper limit of this time, 10.7 ± 0.6My, is obtained if we assume that Y-82192/3 was not exposed to cosmic rays in the lunar regolith, i.e. that it was excavated from a depth completely shielded from cosmic rays by the same impact that launched it into Earth orbit. The lower limit for the Moon-Earth transit time, about 5 My, is given by the fact that 1.6 My10Be is present in equilibrium activity for a 4π exposure. If the Y-82192/3 material was ever exposed to cosmic rays in the lunar regolith this exposure must have lasted less than 11 My at shallow shielding of ⩽ 25 g/cm2. Abundances of trapped solar wind particles are extremely low. Only solar wind Ne and Ar could definitely be detected. Comparison of the histories of lunar meteorites Allan Hills A-81005 and Yamato-791197 studied earlier with the data for Yamato-82192/3 shows that at least two impacts on the Moon are responsible for ejecting the lunar meteorites which have so far been found on Earth.

81Kr-Kr exposure ages and the isotopic abundances of He, Ne, Ar, Kr, and Xe were measured for thirteen ordinary chondrites. Together with the 81Kr-Kr ages for four chondrites obtained earlier in our laboratory and two chondrites reported by other authors, this data base is used to derive cosmic-ray production rates for 3He, 21Ne, 38Ar, 83Kr, and 126Xe. Production rates are obtained as a function of the shielding dependent cosmogenic ratio (22Ne21Ne)c and of the chemical composition of CI, CM, CO, CV, H, L, LL, EH, and EL chondrites. The following production rate equations are proposed (P3),P21, and P38in units of 10−8 cm3 STP/g per Ma, P83and P126 in 10−12 cm3 STP/g per Ma): P3 = F[2.09 − 0.43(22Ne21Ne)c], FCI = 1.01, FCM = 1.00, FCO = 0.99, FCV = 0.99, FH = 0.98 , FL=1.00, FLL=1.00, Feh = 0.97, and FEL = 1.00 . P21 = 1.61F[21.77(22Ne21Ne)c− 19.32]−1, FCI = 0.67, FCM = 0.79, FCO = 0.96, FCV = 0.96, FH = 0.93 , FL=1.00, FLL=1.00, FEH = 0.78, and FEL = 0.96 . P38 = F[0.125 − 0.071(22Ne21Ne]c, FCI, = 0.75, FCM = 0.88, FCO = 1.03, FCV = 1.10, FH = 1.08 , FL=1.00, FLL=1.00, FEH = 0.98, and FEL = 0.89 . P83 = 0.0196F[0.62(22Ne21Ne)c − 0.53]−1, FCI = 0.71, FCM = 0.94,ifCO = 1.02, FCV = 1.13, FH = 1.00 , FL=1.00, FLL=1.00, FEH = 0.75, and FEL = 0.80 . P126 = F[0.0174 − 0.0094(22Ne21Ne)c], FCI = 0.66, FCM = 0.93, FCO = 1.18, FCV = 1.40, FH = 1.00 , FL = 1.00, FLL = 1.00, FEH = 0.72, and FEL = 0.72 . Exposure ages were calculated from cosmogenic 3He, 21Ne, and 38Ar concentrations in eleven chondrites which lack Kr data. The good agreement of the ages derived from different noble gases demonstrates the consistency of the adopted production rates. Finally, noble gas data from mineral separates and from stepped temperature fractions show that Kr and Xe extracted between 700 and 1200°C from a feldspar-rich separate have large excesses of the cosmogenic component. This should result in more accurate 81Kr-Kr and 126Xe ages than bulk chondrite analyses.

Noble gases in four sediment samples from the Cretaceous-Tertiary boundary collected near Stevns in Denmark were investigated to test the possibility of the presence of noble gases indicative for meteorites. All samples were also analyzed for the noble metals Os and Ir and twelve other elements. The observed enrichments of3He,4He and of Ar, Kr, and Xe relative to atmospheric abundances can be explained without invoking the addition of extraterrestrial material. The 20Ne/22Ne ratio and the Kr and Xe isotopic compositions are identical with the isotopic ratios in the terrestrial atmosphere. In contrast, the high noble metal concentrations indicate the presence of material with elemental abundances similar to chondritic matter. Compared to noble metals the noble gases are less sensitive tracers of an admixture of extraterrestrial matter in sediments.

In large asteroidal or cometary impacts on the moon, lunar surface material can be ejected with escape velocities. A few of these rocks were captured by Earth and were recently collected on the Antarctic ice. The records of noble gas isotopes and of cosmic ray-produced radionuclides in five of these meteorites reveal that they originated from at least two different impact craters on the moon. The chemical composition indicates that the impact sites were probably far from the Apollo and Luna landing sites. The duration of the moon-Earth transfer for three meteorites, which belong to the same fall event on Earth, lasted 5 to 11 million years, in contrast to a duration of less than 300,000 years for the two other meteorites. From the activities of cosmic ray-produced radionuclides, the date of fall onto the Antarctic ice sheet is calculated as 70,000 to 170,000 years ago.