244 research outputs found
Recommended from our members
The distribution of asteroids: evidence from Antarctic micrometeorites
The relative abundances of types amongst 550 AMMs are reported. These suggest that C-type asteroids vary from petrologic type 1 to 3.2 and that the majority of S-type asteroids are chondrule-rich
Recommended from our members
Microbial D/H fractionation in extraterrestrial materials: application to micrometeorites and Mars
High D/H terrestrial alteration of micrometeorites is described and suggested to be a result of microbial isotopic fractionation by methanogens. Applications to other planetary materials, including martian meteorites, are also considered
The weathering of micrometeorites from the Transantarctic Mountains
Micrometeorites are cosmic dust particles recovered from the
Earth's surface that dominate the influx of extraterrestrial material
accreting to our planet. This paper provides the first in-depth study of
the weathering of micrometeorites within the Antarctic environment that
will allow primary and secondary features to be distinguished. It is
based on the analysis of 366 particles from Larkman Nunatak and 25 from
the Transantarctic Mountain collection. Several important morphological
categories of weathering effects were identified: (1) irregular and
faceted cavities, (2) surface etch pits, (3) infilled cavities, (4)
replaced silicate phases, and (5) hydrated and replaced metal. These
features indicate that congruent dissolution of silicate phases, in
particular olivine, is important in generating new pore space within
particles. Comparison of the preservation of glass and olivine also
indicates preferential dissolution of olivine by acidic solutions during
low temperature aqueous alteration. Precipitation of new hydrous phases
within cavities, in particular ferrihydrite and jarosite, results in
pseudomorph textures within heavily altered particles. Glass, in
contrast, is altered to palagonite gels and shows a sequential
replacement indicative of varying water to rock ratios. Metal is variably
replaced by Fe-oxyhydroxides and results in decreases in Ni/Fe ratio. In
contrast, sulphides within metal are largely preserved. Magnetite, an
essential component of micrometeorites formed during atmospheric entry,
is least altered by interaction with the terrestrial environment. The
extent of weathering in the studied micrometeorites is sensitive to
differences in their primary mineralogy and varies significantly with
particle type. Despite these differences, we propose a weathering scale
for micrometeorites based on both their degree of terrestrial alteration
and the level of encrustation by secondary phases. The compositions and
textures of weathering products, however, suggest open system behaviour
and variable water to rock ratios that imply climatic variation over the
lifetime of the micrometeorite deposits
Recommended from our members
Ancient Cosmic Dust from Triassic Halite
We describe the discovery of fossil micrometeorites in ancient Triassic rock salt; the first to be found in salt and the oldest complete micrometeorites found to date. We present an estimated flux rate of micrometeorites to Earth at this time
Recommended from our members
Cryptoendolith alteration of Antarctic sandstone substrates: pioneers or opportunists?
The cryptoendolithic habitat of the Antarctic Dry Valleys has been considered a good analogy for past Martian ecosystems, if life arose on the planet. Yet cryptoendoliths are thought to favor the colonization of rocks that have a preexisting porous structure, e. g., sandstones. This may weaken their significance as exact analogues of potential rock-colonizing organisms on Mars, given our current understanding of the dominant volcanic nature of Martian geology. However, the production of oxalic acid, by these lichendominated communities, and its weathering potential indicate that it could be an aid in rock colonization, enabling endoliths to inhabit a wider variety of rock types. Utilizing ICP-AES and scanning electron microscope techniques, this study investigates elemental and mineralogical compositions within colonized and uncolonized layers in individual sandstone samples. This is in order to determine if the weathering of mineral phases within the colonized layers causes an increase in the amount of pore space available for colonization. The results show that colonized layers are more weathered than uncolonized, deeper portions of the rock substrate. Layers within uncolonized samples have uniform compositions. Differences between the colonized and uncolonized layers also occur to varying extents within colonized rocks of different mineralogical maturities. The results confirm that cryptoendoliths modify their habitat through the production of oxalic acid and suggest that over time this directly increases the porosity of their inhabited layer, potentially increasing the biomass it can support
Recommended from our members
Cryptoendolith colonization of diverse substrates (1): cultivation and characterization
We are investigating whether cryptoendolithic microorganisms are able to colonize diverse substrates through biogenic weathering. This first part of the study involves the cultivation and characterization of microbial consortia from Antarctic sandstone habitats
Recommended from our members
The petrology of fine-grained micrometeorites: Evidence for the diversity of primitive asteroids
We report the discovery by analytical TEM of serpentine and phases interpreted as dehydroxylates of serpentine in ultramicrotomed sections of a number of fine-grained Antarctic micrometeorites
The effect of composition and zoning on infra-red spectra of the Martian silicate minerals
http://www.lpi.usra.edu/meetings/lpsc2012/pdf/2199.pd
Cobalt and chromium exposure affects osteoblast function and impairs the mineralization of prosthesis surfaces in vitro.
Cobalt (Co) and chromium (Cr) ions and nanoparticles equivalent to those released through tribo-corrosion of prosthetic metal-on-metal (MOM) bearings and taper junctions are detrimental to osteoblast activity and function in-vitro when examined as individual species. Here we examined the effects of Co(2+) :Cr(3+) and Co(2+) :Cr(6+) combinations on osteoblast-like SaOS-2 cellular activity, alkaline phosphatase (ALP) activity and mineralization to better reflect clinical exposure conditions in vivo. We also assessed the effect of Co(2+) :Cr(3+) combinations and Co:Cr nanoparticles on SaOS-2 cell osteogenic responses on grit-blasted, plasma-sprayed titanium-coated and hydroxyapatite-coated prosthesis surfaces. Cellular activity and ALP activity were reduced to a greater extent with combination treatments compared to individual ions. Co(2+) and Cr(3+) interacted additively and synergistically to reduce cellular activity and ALP activity respectively, whilst the Co(2+) with Cr(6+) combination was dominated by the effect of Cr(6+) alone. Mineralization by osteoblasts was greater on hydroxyapatite-coated surfaces compared to grit-blasted and plasma-sprayed titanium-coated surfaces. Treatments with Co(2+) :Cr(3+) ions and Co:Cr nanoparticles reduced the percentage mineralization on all surfaces, with hydroxyapatite-coated surfaces having the least reduction. In conclusion, our data suggests that previous studies investigating individual metal ions underestimate their potential clinical effects on osteoblast activity. Furthermore, the data suggests that hydroxyapatite-coated surfaces may modulate osteoblast responses to metal debris. This article is protected by copyright. All rights reserved
- …