Helium in Stone Meteorites.

Eberhardt, P.; Hess, David C.

doi:10.1086/146804

Cited by 54 publications

(15 citation statements)

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“…Although space erosion is undoubtedly of some importance, most workers no longer consider it to be the dominant factor; partly because there seems to be no correlation between friability and age, and partly because the erosion rates in the ion bombardment of stones and irons turn out to be nearly identical (HEYMANN and FLUIT, 1962;HEYMANN, 1964). EBERHARDT and HESS (1960) therefore suggested an alternative explanation: that the stones were being preferentially destroyed by collisions with other meteorites. This is probably the most satisfactory explanation of the scarcity of stones with high exposure ages.…”

Section: Collision Lifetimes and Exposure Agesmentioning

confidence: 99%

Origin, age, and composition of meteorites

1964

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There are perhaps as many opinions as to the origin of meteorites as there are students of meteorites. Probably in no other branch of natural science is there such a wealth of observational data coupled with such a lack of unanimity in interpretation." (WooD, 1963a) Abstract. This paper attempts to bring together and evaluate all significant evidence on the origin of meteorites.The iron meteorites seem to have formed at low pressures. Laboratory evidence shows that the absence of a Widmanst~itten pattern in meteorites with ~ 16 ~ Ni cannot be attributed to high pressures, but to supercooling or an unusually last cooling rate for these meteorites, which prevented the development of a pattern. The presence of tridymite in the Steinbach siderophyre provides further, direct proof that the Widmanst/itten pattern can form at pressures less than 3 kb. Neither diamond, nor cliftonite, nor cohenite are reliable pressure indicators in meteorites. Diamonds were formed by shock while cliftonite may have been derived from a cubic carbide such as Fe4C. Cohenite is apparently stabilized by kinetic rather than thermodynamic factors. Several lines of evidence suggest that the irons come from more than one parent body, perhaps as many as four.The frequency of pallasites is perfectly consistent with an origin in the transition zone between core and mantle of the parent body. "Hybrid" meteorites such as Brenham are not necessarily derived from the metal-silicate interface, but probably resulted from dendrite growth in the solidifying melt.Ordinary chondrites definitely are equilibrium assemblages rather than chance conglomerates. According to the best available evidence, Prior's rules seem to be valid. The metal particles in chondrites differentiated into kamacite and taenite in their present location, rather than in a remote earlier environment. Trace element abundances in ordinary and carbonaceous chondrites suggest that these meteorites accreted from two types of matter: an undepleted fraction that separated from its complement of gases at low temperatures, and a depleted fraction that lost its gases at high temperatures. These two fractions of primitive meteoritic matter are tentatively identified with the matrix and chondrules-phis-metal, respectively. New restrictive limits are placed on the iron-silicate fractionation in chondrites. No direct evolutionary path exists that connects the currently accepted solar abundances of Fe and Ni and the observed Fe/Si and Ni/Si ratios in chondrites. Apparently the solar abundance of iron is in error. The iron-silicate fractionation seems to have occurred while chondritic matter was in a more strongly reduced state than its present one.The U-He and K-At ages of hypersthene chondrites are systematically shorter than those of bronzite chondrites. Short ages are correlated with shock effects, and it seems that the hypersthene chondrites suffered reheating and partial-to-complete outgassing 0.4 AE ago. The cosmic-ray exposure ages of all classes of meteorite s cluster distinctly, indicating th...

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Section: Collision Lifetimes and Exposure Agesmentioning

confidence: 99%

Origin, age, and composition of meteorites

1964

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“…Over the years, several analyses of T. systematics were carried out. Conclusions regarding collisional destruction rates (Eberhardt & Hess 1960, Gault 1969, origin of meteorites (Arnold 1965, Wanke 1966, Wetherill 1985, parent-body stratigraphy (Crabb & Schultz 1981), and collisional breakup events (Geiss et a1 1960, Anders 1964 were based on the distribution and clustering of exposure ages. Variations in T. systematics of different petrographic types among the chondrites as well as for gas-rich chondrites were considered by Crabb & Schultz (1981).…”

Section: Introductionmentioning

confidence: 99%

Cosmic-Ray Exposure History of Ordinary Chondrites

Marti¹,

Graf²

1992

Annu. Rev. Earth Planet. Sci.

201

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“…It is quite possible that this distribution would be narrowed considerably if radiation ages could be obtained from He 3 /H 3 ratios, just as it is the case with chondrites for which tritium contents are known. However, in some cases (for instance BEARDSLEY 18 or NADIABONDI 19 ) the He 3 contents are so much different from the average that radiation ages close to 22 m. y. cannot be expected for these falls, unless there exist much larger variations in production rates than those known from tritium determinations up to now.…”

Section: Radiation Ages Of Chondritesmentioning

confidence: 95%

Notizen: Radiation Ages of Chondrites

Geiss

Oeschger

Signer

1960

Zeitschrift Für Naturforschung A

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[1960] (im Erscheinen). The concentrations of tritium and of all the isotopes of helium, neon, and argon have been determined in some chondrites. The technical procedures have been described briefly in previous publications 1 ' 2 . The results pertinent to this note are summarized in a tritium measurement. Our rare gas results agree reasonably well with those of GOEBEL et al. Radiation Ages of ChondritesRadiation ages are calculated from He 3 /H 3 ratios, assuming equal direct production rates for tritium and helium-3. He 4 and A/K ages are estimated on the basis of the average contents of the elements uranium, thorium, and potassium in chondrites which are U = 1.1 • 10 -8 g/g 3 , Th/U = 3.6 4 , and K = 0.085% 5 < 6 . These ages are given in table 2, together with those from chondrites for which He 3 /H 3 radiation ages have been published before 8 . The results from Abee by BEGEMANN et al. 9 are not included here, as this stone is an achondrite according to UREY and MAYEDA 10 . In the histogram (Fig. 1) we have distinguished between two groups of chondrites: those with high and those with low radioactive He 4 and A/K ages. It is remarkable that all the chondrites belonging to the first 6

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Helium in Stone Meteorites.

Cited by 54 publications

References 0 publications

Origin, age, and composition of meteorites

Origin, age, and composition of meteorites

Cosmic-Ray Exposure History of Ordinary Chondrites

Notizen: Radiation Ages of Chondrites

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