Thesis (Ph.D.)--University of Adelaide, School of Chemistry and Physics, 2003? / "July 2003." Includes bibliographical references (leaves 459-484). Also available in a print form.

This dissertation is an exploration of the effects of the collision of large asteroids and comets on the atmosphere of the Earth and Earthlike planets. The first task undertaken is the characterization of the impact rates in the inner solar system during the present time, and during the first billion years of Solar System history when the flux was changing rapidly. Once defined, these fluxes are used to model the long term cumulative effect of multiple impacts on planetary atmospheres. The implications of cometary impacts on evolution of the water and deuterium abundances on Venus are examined. The short lifetime of water on Venus suggests that the water abundance is in a quasi-steady-state balance between loss by escape and replenishment by infall. In addition, the observed deuterium-to-hydrogen ratio on Venus is consistent with a steady state and does not necessarily imply a past water excess. Results are presented of a model incorporating a stochastic cometary source and nonthermal escape of hydrogen that produces the observed water abundance and D/H ratio. The stochastic variability of each of these quantities is shown to be large. Water on Venus is likely to be in a near steady state mediated by large comet impacts. The early history of water on the planet has been obscured by a history of random impacts. A study of the effects of impact-generated dust clouds on the primitive Earth leads to the conclusion that such clouds were significant perturbers of the early climate. The Earth was shrouded by an optically-thick dust cloud for ≈ 150-250 m.y. During this time the surface temperature was equal to the planetary equilibrium temperature unless significant heating by impacts or surface heat flow existed beneath the dust cloud. An admixture of a few per cent of organic materials in the cloud may have significantly lowered the planetary bond albedo, thereby raising the equilibrium temperature. The epoch of continuous dust shrouding was followed by a period of stochastically intermittent dust clouds occuring at greater intervals as the early intense bombardment subsided towards the present day flux.

No description available.

Nearly 100 chondrules were extracted from -8.6g of the Mokoia (CV3) meteorite and have been analyzed by sequential instrumental neutron activation analysis (INAA). The resulting data were utilized in a comprehensive statistical characterization of these objects and, unlike similar investigations, virtually no loss of relevant data was incurred due to the use of inadequate or inappropriate software. Mass and elemental frequency distributions, correlation analysis and sorting coefficients support a "nebular" setting for chondrule genesis, and a scenario in which interstellar "dust-balls" (= chondrule precursors) are subject to some transient (short duration) high-energy process(es) followed by gravitationally or aerodynamically induced sorting, while it appears that an enhanced oxygen fugacity due to particle/gas fractionation may also be a factor. Conversely, a "planetary" setting for chondrule formation which requires the melting of pre-existing rocks (e.g., incompatible with the observed data. Factor analysis has led to the identification of the following precursor assemblages (i.e., factors) in the Mokoia chondrite: a refractory lithophile phase, a siderophile/chalcophile phase, a Mg-rich (silicate ?) phase, a refractory siderophile phase and a common lithophile phase. Previous studies of the Allende (CV3), Ornans (C03), Semarkona (LL3) and Chainpur (L3) meteorites are compared with these findings and interchondrite relationships are discussed (e.g., do these objects share similar parental materials, or are their compositions somehow complementary? were they formed in proximity with each other? etc.). A very unique oxide-sulfide-phosphate opaque assemblage was found in Mokoia and analyzed by INAA/electron-probe microanalysis, and may eventually serve to place constraints on the low-temperature thermal histories of chondrules or chondrites as well as provide information concerning the oxygen and sulfur fugacities within the Mokoia chondrite parent body. / Graduation date: 1991

Bound with: British Museum. A guide to the exhibition galleries. 1879. / Signed: Nevil Story-Maskelyne, Nov. 1, 1877.

No description available.

Prior to their retrieval from low Earth orbit (LEO), the individual solar cells that make up the 'V2' solar array panel from the Huhble Space Telescope (HST) were prone to hypervelocity (>5 km/s ) impact damage from micrometeoroids and space debris. The analysis of such passive collector surfaces allows sampling of micrometeoroids that have not undergone any terrestrial atmospheric alteration and better defines the population of space debris particles below the lmm size range. Herein a new approach has been taken to try and identify the nature atid origin of impact derived residues generated in the individual solar cells from the HST. A total of 25 solar cells were selected on the basis that they contained impact craters (100-1000?n diameter) rather than larger impact holes (1-3mm diameter), as preliminary studies indicated that they were more likely to retain impact residues. These were subsequently analysed using digitised hack-scattered electron imaging, coupled with digitised x-ray elemental mapping and micro-spot analysis to locate, identify and classify the residues. 29 impact craters were located on solar cells. In the analysis of the residues; 3 were identified residues as space debris in origin, 6 unclassified and 20 as micrometeoroid. The space debris derived residues were identified as remnants of a paint fragment, a stainless steel particle and a fragment of a printed circuit board. The micrometeoroid derived residues were sub-classified in terms of mineral chemistry, with apparent mafic- and phyllo- silicates being the dominant components, with minor iron-nickel metal and iron sulfides, suggesting a broadly chondritic origin. Fe-Ni rich residue was also identified that would appear to belong to a group of non-chondritic particles previously unrecognised. Possible refractory or Ca/Al rich inclusions from a primitive micrometeoroid were also observed as near intact Ca-rich fragments, the textures of the individual grains suggested that they were not merely terrestrial contamination. Laboratory impact studies, using a light-gas-gun to accelerate small fragments (125- 250?m) of known meteorite mineralogies up to 5km/s, and then impact them into solar cells have generated a suite of residues that are analogues of those observed from LEO studies. The silicate minerals generated residues that were intimately associated with the host melt glass. Metallic sulfides and metals generated surface and sub-surface immiscible droplets. Several craters also contained near-intact fragments of minerals. Overall. despite the small sample set examined. the observed dominance of micrometeoroid to space debris residue chemistry (correlating to particle size range of 8-80 ?m) corresponds well to the accepted flux models.

Thesis (M.S.)--University of Hawaii at Manoa, 2008. / Includes bibliographical references (leaves 208-234). / xiv, 234 leaves, bound ill. (some col.) 29 cm

Bound with: British Museum. A guide to the exhibition galleries. 1879. / Signed: Nevil Story-Maskelyne, Nov. 1, 1877.

Thesis (Ph. D.)--Columbia University, 1934. / Vita. Bibliography: p. 34-35.