Richard P. Feynman 1918-1988

Richard Feynman, simply put, was a genius. His quick wit and uncommon grasp of physics meant that any research area he encountered, he quickly mastered. Despite the fact that his own area of research was not geophysics, his life and work influenced almost all of us. Virtually every physics graduate student who started in the mid 60s or later was exposed to his Lectures on Physics, either by having them as a text for a course or by using them (as I did) to bone up for oral qualifying exams. Feynman diagrams appear in nearly every modern quantum mechanics textbook and are featured in his official Caltech portrait, which illustrates this article

Nitrogen Isotopes in Silicon Carbide: Stellar Nucleosynthesis?

Nitrogen in presolar SiC varies over a wide range of concentrations and is typically ^(14)N-rich relative to solar N, consistent with ^(15)N being consumed during CNO processing in stellar envelopes [e.g., 1]. Although C is also heavily processed in the envelopes [1], no clear isotopic correlation exists between C and N [e.g., 2], making N compositions difficult to interpret. Although the same general N features are seen in SiC from many meteorites, clear differences between meteorites have also been observed. In particular, Murchison SiC appears to have systematically higher ^(15)N/^(14)N ratios than Orgueil SiC [2,3]. Among ISN-poor SiC grains for both meteorites, ^(15)N/^(14)N and ^(28)Si/^(l4)N exhibit a positive correlation (Fig. 1)

Europium valence state distributions in equilibrated ordinary chondrites

It has been recognized for 30 years that the presence of Eu anomalies in REE patterns is due to the presence of divalent Eu, unique among the REE. However, it has not previously been possible to infer quantitative Eu^(+2)/Eu^(+3) ratios in natural samples. We have used ion probe data for lithophile trace elements for the phases in equilibrated ordinary chondrites [Guareiia (H6), Marion (L6) and St. Sevérin (LL6)] to perform mass-balance calculations that yield relatively precise Eu^(+2)/Eu^(+3) ratios

The Formation and Evolution of the First Massive Black Holes

The first massive astrophysical black holes likely formed at high redshifts (z>10) at the centers of low mass (~10^6 Msun) dark matter concentrations. These black holes grow by mergers and gas accretion, evolve into the population of bright quasars observed at lower redshifts, and eventually leave the supermassive black hole remnants that are ubiquitous at the centers of galaxies in the nearby universe. The astrophysical processes responsible for the formation of the earliest seed black holes are poorly understood. The purpose of this review is threefold: (1) to describe theoretical expectations for the formation and growth of the earliest black holes within the general paradigm of hierarchical cold dark matter cosmologies, (2) to summarize several relevant recent observations that have implications for the formation of the earliest black holes, and (3) to look into the future and assess the power of forthcoming observations to probe the physics of the first active galactic nuclei.Comment: 39 pages, review for "Supermassive Black Holes in the Distant Universe", Ed. A. J. Barger, Kluwer Academic Publisher

The solubility of quartz at high temperatures and pressures

In a recent paper by J. A. Wood, Jr. (this Journal, v. 256, p. 40, 1958) a theoretical discussion of the experimental data on the solubility of quartz in water was presented

On the formation of Fe-Ni metal in Renazzo-like carbonaceous chondrites

The Fe-Ni metal within chondrites has been postulated to have originated either through condensation or as a byproduct of chondrule formation. To test these hypotheses, we studied metal in three Renazzo-like carbonaceous (CR2) chondrites from three petrographic settings: inside chondrules, on chondrule rims, and in the matrix. Abundances of Fe, Ni, Co, Cr, and P were determined in situ by electron microprobe, and those of Os, Ir, Pt, and Au were measured by a newly developed ion microprobe technique. The refractory platinum group elements Os, Ir, and Pt behave coherently in CR2 metal. They are either all enriched, all depleted, or unfractionated with respect to Fe and cosmic ratios. Metal with approximately CI Os/Fe, Ir/Fe, and Pt/Fe occur primarily in chondrule interiors. All metal grains have essentially CI values of Ni/Fe and Co/Fe. Almost all metal grains have lower-than-CI ratios of the volatile elements, Au and P. We also estimated the bulk compositions via analyses of phases and modal recombination of a subset of the chondrules whose metal we analyzed. The bulk compositions of chondrules are generally unfractionated relative to CI chondrites for elements more refractory than ∼Cr but are depleted in more volatile elements. Abundances of siderophile elements correlate strongly with the metal abundance in the chondrules, which implies that siderophile depletions are due to expulsion of metal from the chondrule melts. The metal most likely originated during melting via reduction of oxides by C that was part of the chondrule precursor. During chondrule heating, molten metal efficiently extracted siderophile elements from the silicate melt. Rim metal consists of two types. One is like metal in chondrule interiors and was in the process of being expelled when the chondrules were quenched. The other shows systematic depletions in Os, Ir, and Pt relative to Fe and higher concentrations of Au and P than interior metal. This metal is attributed to recondensation from a vapor depleted in refractory siderophiles, a vapor most likely derived via evaporation from chondrules. Large, isolated matrix metal grains comprise the same two groups as rim grains and have the same origins. Bulk chondrule compositions and siderophile abundance patterns in metal indicate that the precursors of CR2 chondrules had CI-like abundances of refractory and moderately volatile elements but was likely depleted in the more volatile elements

A neodymium, strontium, and oxygen isotopic study of the Cretaceous Samail ophiolite and implications for the petrogenesis and seawater-hydrothermal alteration of oceanic crust

In the Samail ophiolite, ^(147)Sm-^(143)Nd,^(87)Rb-^(87)Sr, and ^(18)O/^(16)O isotopic systems have been used to distinguish between sea-floor hydrothermal alteration and primary magmatic isotopic variations. The Rb-Sr and ^(18)O/^(16)O isotopic systems clearly exhibit sensitivity to hydrothermal interactions with seawater while the Sm-Nd system appears essentially undisturbed. Internal isochrons have been determined by the ^(147)Sm-^(143)Nd method using coexisting plagioclase and pyroxene and give crystallization ages of 130 ± 12m.y. from Ibra and 100 ± 20 m.y. from Wadi Fizh. These ages are interpreted as the time of formation of the Samail oceanic crust and are older than the inferred emplacement age of 65–85 m.y. The initial ^(143)Nd/^(144)Nd ratios for a tectonized harzburgite, cumulate gabbros, plagiogranite, sheeted dikes and a basalt have a limited range in ε_(Nd) of from 7.5 to 8.6 for all lithologies, demonstrating a clear oceanic affinity and supporting earlier interpretations based on geologic observations and geochemistry. The ^(87)Sr/^(86)Sr initial ratios on the same rocks have an extremely large range of from 0.70296 to 0.70650 (ε_(Sr) = −19.7 to +30.5) and the δ^(18)O values vary from 2.6 to 12.7. These large variations are clearly consistent with hydrothermal interaction of seawater with the oceanic crust. A model is presented for the closed system exchange of Sr and O, that in principle illustrates how the Sr isotopic data may be utilized to estimate the water/rock ratio and subsequently used to evaluate the temperature of equilibration between the water and silicates from the ^(18)O/^(16)O water-rock fractionation