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Description: Clustering of cosmic-ray exposure ages of H chondritic meteorites occurs at 7 {+-} 3 and 30 {+-} 6 Myr ago. There is independent evidence that comet storms have occurred at the same times, based on the fossil record of family and genus extinctions, impact craters and glass, and geomagnetic reversals. We suggest that H chondrites were formed by the impact of shower comets on asteroids. The duration of the most recent comet shower was {le} 4 Myr, in agreement with storm theory.
Date: October 1, 1987
Creator: Perlmutter, S. & Muller, R.A.
Partner: UNT Libraries Government Documents Department

Comparison with European observations of meteor impact

Description: A model for the inference of object size and speed from observations is used to discuss European observations of impact. It compares the observed and predicted breakup altitudes for the objects larger than one meter and observes useful correlations. Trends in magnitude correlate well with measured velocities, altitudes, and trajectories and inferred size and strength parameters, but each parameter is subject to dispute, which can only be addressed when the sensitivity of predictions to uncertainties in these parameters is assessed.
Date: June 1, 1997
Creator: Canavan, G. H.
Partner: UNT Libraries Government Documents Department


Description: In order to decide the value and type of information to be obtained from outer space with regard to its pertinence for the evolution of life, a brief review is presented of the current status of our thinking on the origin of life on earth. This points up the particular kinds of chemicals whose presence, or absence, on other astral bodies might be significant. Heretofore, the only data available are the result of telescopic spectroscopy. We report here information indicating the presence in meteorites of complex organic materials, some of them apparently uniquely pertinent to life processes.
Date: December 7, 1959
Creator: Calvin, Melvin & Vaughn, Susan K.
Partner: UNT Libraries Government Documents Department

Mass Estinctions Caused by Large Bolide Impacts

Description: In this talk, I will describe the wealth of evidence that has forced my colleagues and me to conclude that the great mass extinctions, 65 million years ago, were caused by a large bolide impact on the earth. Bolide is a new word to most people, and it means any piece of solar system debris, such as a meteorite, asteroid, or comet nucleus. As I will show, the bolide responsible for the extinction of most of the then existing species, including the dinosaurs, was about 10 kilometers in diameter.
Date: January 1, 1987
Creator: Lavarez, Luis W.
Partner: UNT Libraries Government Documents Department

Ultrafast growth of wadsleyite in shock-produced melts and its implications for early solar system impact processes

Description: We observed micrometer-sized grains of wadsleyite, a high-pressure phase of (Mg,Fe)2SiO4, in the recovery products of a shock experiment. We infer these grains crystallized from shock-generated melt over a time interval of <1 fs, the maximum time over which our experiment reached and sustained pressure sufficient to stabilize this phase. This rapid crystal growth rate (=1 m/s) suggests that, contrary to the conclusions of previous studies of the occurrence of high-pressure phases in shock-melt veins in strongly shocked meteorites, the growth of high-pressure phases from the melt during shock events is not diffusion-controlled. Another process, such as microturbulent transport, must be active in the crystal growth process. This result implies that the times necessary to crystallize the high-pressure phases in shocked meteorites may correspond to shock pressure durations achieved on impacts between objects 1-5 m in diameter and not, as previously inferred, =1-5 km in diameter. These results may also provide another pathway for syntheses, via shock recovery, of some high-value, high-pressure phases.
Date: December 1, 2009
Creator: Tschauner, Oliver; Asimow, Paul; Kostandova, Natalia; Ahrens, Thomas; Ma, Chi; Sinogeikin, Stanislav et al.
Partner: UNT Libraries Government Documents Department

Comparison with Russian analyses of meteor impact

Description: The inversion model for meteor impacts is used to discuss Russian analyses and compare principal results. For common input parameters, the models produce consistent estimates of impactor parameters. Directions for future research are discussed and prioritized.
Date: June 1, 1997
Creator: Canavan, G. H.
Partner: UNT Libraries Government Documents Department

Soft x-ray shock loading and momentum coupling in meteorite and planetary materials.

Description: X-ray momentum coupling coefficients, C{sub M}, were determined by measuring stress waveforms in planetary materials subjected to impulsive radiation loading from the Sandia National Laboratories Z-machine. Results from the velocity interferometry (VISAR) diagnostic provided limited equation-of-state data as well. Targets were iron and stone meteorites, magnesium rich olivine (dunite) solid and powder ({approx}5--300 {mu}m), and Si, Al, and Fe calibration targets. All samples were {approx}1 mm thick and, except for Si, backed by LiF single-crystal windows. The x-ray spectrum included a combination of thermal radiation (blackbody 170--237 eV) and line emissions from the pinch material (Cu, Ni, Al, or stainless steel). Target fluences 0.4--1.7 kJ/cm{sup 2} at intensities 43--260 GW/cm{sup 2} produced front surface plasma pressures 2.6--12.4 GPa. Stress waves driven into the samples were attenuating due to the short ({approx}5 ns) duration of the drive pulse. Attenuating wave impulse is constant allowing accurate C{sub M} measurements provided mechanical impedance mismatch between samples and the window are known. Impedance-corrected C{sub M} determined from rear-surface motion was 1.9--3.1 x 10{sup -5} s/m for stony meteorites, 2.7 and 0.5 x 10{sup -5} s/m for solid and powdered dunite, 0.8--1.4 x 10{sup -5}.
Date: December 1, 2010
Creator: Lawrence, R. Jeffery; Remo, John L. & Furnish, Michael David
Partner: UNT Libraries Government Documents Department

Geochemical anomalies near the Eocene-Oligocene and Permian-Triassic boundaries

Description: Evidence is presented to support the theory that several mass extinctions, i.e., those that define the Permian-Triassic boundary, the Cretaceous-Tertiary boundary, and the Eocene-1 Oligocene boundary, were caused by impact on the earth of extraterrestrial objects having the composition of carbonaceous chondrites and diameters of about 10 km. The evidence consists of anomalously high concentrations of iridium and other siderophile elements at the stratigraphic levels defining the extinctions. (ACR)
Date: October 1, 1981
Creator: Asaro, F.; Alvarez, L.W.; Alvarez, W. & Michel, H.V.
Partner: UNT Libraries Government Documents Department


Description: The study of meteorite Murray has been reported in previous Quarterly Reports. This report gives further results with Murray, and information on another meteorite, Orgueil. A sample of Orgueil was sent from the Museum National d Histoire Naturelle, Paris. It fell in several pieces over an area of 2 square miles near Orgueil, France, in 1864. The elemental analysis of this meteorite is shown in Table 1. They extracted a 10.07-g sample of this meteorite with water, using the same procedure as that for Murray. The water extracted 1.32 g, which is at least twice as much material as was water-extracted from Murray. The elemental analysis of the water extract is given in Table II and its uv spectrum is shown in Figure 1. From an x-ray diffraction pattern it was determined that the water extract contained mostly MgSO{sub 4} {center_dot} 6H{sub 2}O with some calcium sulfate. Their spectrum (Figure 2) shows a strong SO{sub 4} band at 1100 cm{sup -1}, = strong H{sub 2}O bands at 1650 cm{sup -1} and 3200-3600 cm{sup -1}, and some unidentified peaks at 2300, 1400, and 980 cm{sup -1}. The approximately 8 g of Orgueil left after the water extraction was then extracted with purified chloroform. Approximately 50 mg of yellow material was extracted. Its uv spectrum is shown in Figure 3 and is identical to the spectrum of elemental sulfur. Whatever else may be extracted from the meteorites by organic solvents, the uv spectra show only sulfur.
Date: June 29, 1961
Partner: UNT Libraries Government Documents Department

Disturbance of isotope systematics in meteorites during shock and thermal metamorphism and implications for shergottite chronology

Description: Shock and thermal metamorphism of meteorites from differentiated bodies such as the Moon and Mars have the potential to disturb chronometric information contained in these meteorites. In order to understand the impact-related mechanisms and extent of disturbance to isochrons, we undertook experiments to shock and heat samples of 10017, a 3.6 billion year old lunar basalt. One sub-sample was shocked to 55 GPa, a second subsample was heated to 1000 C for one week, and a third sub-sample was maintained as a control sample. Of the isotope systems analyzed, the Sm-Nd system was the least disturbed by shock or heat, followed by the Rb-Sr system. Ages represented by the {sup 238}U-{sup 206}Pb isotope system were degraded by shock and destroyed with heating. In no case did either shock or heating alone result in rotated or reset isochrons that represent a spurious age. In some cases the true crystallization age of the sample was preserved, and in other cases age information was degraded or destroyed. Although our results show that neither shock nor thermal metamorphism alone can account for the discordant ages represented by different isotope systems in martian meteorites, we postulate that shock metamorphism may render a meteorite more susceptible than unshocked material to subsequent disturbance during impact-related heating or aqueous alteration on Mars or Earth. The combination of these processes may result in the disparate chronometric information preserved in some meteorites.
Date: December 10, 2008
Creator: Gaffney, A M; Borg, L E & Asmerom, Y
Partner: UNT Libraries Government Documents Department


Description: We have analyzed available instrumental and eyewitness records associated with the fireball leading to the fall of the Tagish Lake meteorite. Initial chemical and physical studies of this carbonaceous chondrite have shown it to be unique. It is one of the most primitive meteorites yet recovered and extremely friable. By determining the original bodies trajectory, velocity and physical breakup in the atmosphere we can characterise the fireball as intermediate between Type II and Type IIIa, following the classification of Ceplecha et al. Modelling of the object suggests an initial porosity of the pre-atmospheric body in the range 40-60%. The initial fragmentation occurred under less than 0.3 MPa dynamic pressure. Determination of Tagish Lake's orbit suggests a nominal linkage to parent bodies in the main asteroid belt, though association with short-period comets cannot be strictly excluded. It is suggested that Tagish Lake represents an intermediate object between chondritic asteroids and cometary bodies and our results are consistent with a linkage to D-class asteroids based on results from reflectance-spectra work.
Date: January 1, 2001
Creator: Brown, P. G. (Peter G.) & ReVelle, D. O. (Douglas O.)
Partner: UNT Libraries Government Documents Department

The age of the martian meteorite Northwest Africa 1195 and the differentiation history of the shergottites

Description: Samarium-neodymium isotopic analyses of unleached and acid-leached mineral fractions from the recently identified olivine-bearing shergottite Northwest Africa 1195 yield a crystallization age of 348 {+-} 19 Ma and an {var_epsilon}{sub Nd}{sup 143} value of +40.1 {+-} 1.3. Maskelynite fractions do not lie on the Sm-Nd isochron and appear to contain a martian surface component with low {sup 147}Sm/{sup 144}Nd and {sup 143}Nd/{sup 144}Nd ratios that was added during shock. The Rb-Sr system is disturbed and does not yield an isochron. Terrestrial Sr appears to have affected all of the mineral fractions, although a maximum initial {sup 87}Sr/{sup 86}Sr ratio of 0.701614 {+-} 16 is estimated by passing a 348 Ma reference isochron through the maskelynite fraction that is least affected by contamination. The high initial {var_epsilon}{sub Nd}{sup 143} value and the low initial {sup 87}Sr/{sup 86}Sr ratio, combined with the geologically young crystallization age, indicate that Northwest Africa 1195 is derived from a source region characterized by a long-term incompatible element depletion. The age and initial Sr and Nd isotopic compositions of Northwest Africa 1195 are very similar to those of Queen Alexandra Range 94201, indicating these samples were derived from source regions with nearly identical Sr-Nd isotopic systematics. These similarities suggest that these two meteorites share a close petrogenetic relationship and might have been erupted from a common volcano. The meteorites Yamato 980459, Dar al Gani 476, Sayh al Uhaymir 005/008, and Dhofar 019 also have relatively old ages between 474-575 Ma and trace element and/or isotopic systematics that are indicative of derivation from incompatible-element-depleted sources. This suggests that the oldest group of meteorites is more closely related to one another than they are to the younger meteorites that are derived from less incompatible-element-depleted sources. Closed-system fractional crystallization of this suite of meteorites is modeled with the MELTS algorithm ...
Date: April 5, 2007
Creator: Symes, S; Borg, L; Shearer, C & Irving, A
Partner: UNT Libraries Government Documents Department

Uranium-lead isotope systematics of Mars inferred from the basaltic shergottite QUE 94201

Description: Uranium-lead ratios (commonly represented as {sup 238}U/{sup 204}Pb = {mu}) calculated for the sources of martian basalts preserve a record of petrogenetic processes that operated during early planetary differentiation and formation of martian geochemical reservoirs. To better define the range of {mu} values represented by the source regions of martian basalts, we completed U-Pb elemental and isotopic analyses on whole rock, mineral and leachate fractions from the martian meteorite Queen Alexandra Range 94201 (QUE 94201). The whole rock and silicate mineral fractions have unradiogenic Pb isotopic compositions that define a narrow range ({sup 206}Pb/{sup 204}Pb = 11.16-11.61). In contrast, the Pb isotopic compositions of weak HCl leachates are more variable and radiogenic. The intersection of the QUE 94201 data array with terrestrial Pb in {sup 206}Pb/{sup 204}Pb-{sup 207}Pb/{sup 204}Pb-{sup 208}Pb/{sup 204}Pb compositional space is consistent with varying amounts of terrestrial contamination in these fractions. We calculate that only 1-7% contamination is present in the purified silicate mineral and whole rock fractions, whereas the HCl leachates contain up to 86% terrestrial contamination. Despite the contamination, we are able to use the U-Pb data to determine the initial {sup 206}Pb/{sup 204}Pb of QUE 94201 (11.086 {+-} 0.008) and calculate the {mu} value of the QUE 94201 mantle source to be 1.823 {+-} 0.008. This is the lowest {mu} value calculated for any martian basalt source, and, when compared to the highest values determined for martian basalt sources, indicates that {mu} values in martian source reservoirs vary by at least 100%. The range of source {mu} values further indicates that the {mu} value of bulk silicate Mars is approximately three. The amount of variation in the {mu} values of the mantle sources ({mu} {approx} 2-4) is greater than can be explained by igneous processes involving silicate phases alone. We suggest the possibility that ...
Date: December 22, 2006
Creator: Gaffney, A M; Borg, L E & Connelly, J N
Partner: UNT Libraries Government Documents Department

"Ages" of the Sikhote Alin Meteorite

Description: The potassium-argon age of the Siknote Alin iron raeteorite was determined. The value is 1.7 plus or minus 0.2 x 10/sup 9/ years. Previous lead data suggest an age of 4.6 x 10/sup 9/ years. The date of solidification may be the sum of these two ages. (auth)
Date: January 1, 1962
Creator: Sisher, D. E.
Partner: UNT Libraries Government Documents Department


Description: Isotopic assays have been made on the Cr in samples from 14 different chrominiferous minerals from different geographic and meteoritic sources. The results of the assays indicate that it is not possible to state unequivocally that variations in isotopic composition have been observed. (auth)
Date: March 14, 1962
Creator: Svec, H.J.; Flesch, G.D. & Capellen, J.
Partner: UNT Libraries Government Documents Department

Thermal Radiative Heat Transfer to Space From a Body Enclosed by a Semitransparent Body

Description: Bumpers were proposed for protecting space radiator systems from penetration by meteoroids. The development of equations to determine the thermal energy dissipation to space by a hot body completely enclosed by a second body is presented. The particular case of heat dissipation from space radiators enclosed within the bumpers is considered, and the criteria for selection of bumper materials for a minimum weight radiator system are discussed. (auth)
Date: May 1, 1960
Creator: Hefner, R. J.
Partner: UNT Libraries Government Documents Department

Exposure Histories of Lunar Meteorites Northwest Africa 032 and DHOFAR 081

Description: Recent additions to the list of lunar meteorites include Northwest Africa (NWA) 032 and Dhofar 081. NWA 032 is an unbrecciated basalt, found in Morocco; Dhofar 081 is a fragmented feldspathic breccia, found in Oman. Our goal is the determination of the cosmic ray exposure history of these objects. Most lunar meteorites have complex cosmic ray exposure histories, having been exposed both at some depth on the lunar surface (2{pi} irradiation) before their ejection and as small bodies in space (4{pi} irradiation) during transport from the Moon to the Earth. These exposures were then followed by residence on the Earth's surface, the terrestrial residence time. Unraveling the complex history of these objects requires the measurement of at least four cosmogenic nuclides. The specific goals of these measurements are to constrain the depth of the sample at the time of ejection from the Moon, the transit time from the time of ejection to the time of capture by the Earth, and the residence time on the Earth's surface. These exposure durations in conjunction with the sample depth on the Moon can then be used to model impact and ejection mechanisms. To investigate the complex exposure histories of lunar meteorites, we measured cosmogenic nuclides, {sup 36}Cl (half-life = 3.01 x 10{sup 5} yr), {sup 26}Al (7.05 x 10{sup 5} yr), and {sup 10}Be (1.5 x 10{sup 6} yr) in NWA 032 and Dhofar 081. The measurements of {sup 41}Ca (1.04 x 10{sup 5} yr) are in progress.
Date: April 1, 2001
Creator: Nishiizumi, K. & Caffee, M.
Partner: UNT Libraries Government Documents Department

The discovery of fullerenes in the 1.85 billion-year-old Sudbury meteorite crater

Description: Fullerenes (C{sub 60}, C{sub 70}) have been identified by laser time-of-flight and electron-ionization mass spectroscopy in rock samples (black tuff in the Onaping formation) from the crater. They were likely synthesized within the impact plume from carbon contained in the meteorite. The isotopic ratios suggest {sup 13}C enrichment. They are associated with sulfur which may have protected them. This is the largest known deposit of naturally occurring fullerenes.
Date: February 1, 1996
Creator: Becker, L.; Bada, J.L.; Winans, R.E.; Hunt, J.E.; Bunch, T.E. & French, B.M.
Partner: UNT Libraries Government Documents Department

Formation of magnetite and iron-rich carbonates by thermophilic iron-reducing bacteria

Description: Laboratory experiments were performed to study the formation of iron minerals by a thermophilic (45 to 75 C) fermentative iron-reducing bacterial culture (TOR39) obtained from the deep subsurface. Using amorphous Fe(III) oxyhydroxide as an electron acceptor and glucose as an electron donor, TOR39 produced magnetite and iron-rich carbonates at conditions consistent, on a thermodynamic basis, with Eh ({minus}200 mV to {minus}415 mV) and pH (6.2 to 7.7) values determined for these experiments. Analyses of the precipitating solid phases by X-ray diffraction showed that the starting amorphous Fe(III) oxyhydroxide was nearly completely converted to magnetite and Fe-rich carbonate after 20 days of incubation. Increasing bicarbonate concentration in the chemical milieu resulted in increased proportions of siderite relative to magnetite and the addition of MgCl{sub 2} caused the formation of magnesium-rich carbonate in addition to siderite. The results suggest that the TOR39 bacterial culture may have the capacity to form magnetite and iron-rich carbonates in a variety of geochemical conditions. These results may have significant implications for studying the past biogenic activities in the Martian meteorite ALH84001.
Date: June 1, 1997
Creator: Zhang, C.; Liu, S.; Roh, Y.; Cole, D.; Phelps, T.; Vali, H. et al.
Partner: UNT Libraries Government Documents Department

Chinguetti - terrestrial age and pre-atmospheric size

Description: Chinguetti is a 4.5 kg mesosiderite find recovered from the Adra region of Mauretania. In this paper the authors analyse a portion of the recovered sample for cosmogenic radionuclides to determine its terrestrial age, and to determine its pre-atmospheric radius. They determined the terrestrial age of Chinguetti to be < 30 ky. They constrain the pre-atmospheric radius to 50--80 cm and the shielding depths of 15--25 cm. These data indicate that Chinguetti is a comparatively recent fall.
Date: January 14, 2000
Creator: Welten, K C; Masarik, J; Bland, P A; Caffee, M W; Russell, S S; Grady, M M et al.
Partner: UNT Libraries Government Documents Department