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Chilling in Antarctica - meteorites weathering the coldSteer, E. D.; Schwenzer, S. P.; Wright, I. P.; Grady, M. M. (2014-06)Meteorites that fall in Antarctica can reside there for up to 1 Ma before collection . In this time, water can access their inside as thin films along grain boundaries, altering the mineralogy. The alteration products affect the suitability of samples for studies and capture a record of the environmental conditions in which they formed . To better understand the unique processes of cold desert weathering and the chemical signatures that accompany it, this study focuses on the small scale changes caused by proximity of different mineral species to one another. For this, rim and interior thin sections from the L6 chondrite Queen Alexandra Range 94214 were studied, both texturally and chemically using a combination of optical microscopy, SEM, EMPA and LA-ICP-MS at The Open University . Native Fe-Ni, and sulphide minerals are observed to weather initially, causing iron staining to radiate from the weathering minerals across large parts of the meteorite (all of the rim and 40% of the interior). This staining is a visual sign of deposits from the weathering minerals, deposited from a fluid that is likely acidic. We demonstrate how this fluid, derived from the weathering of native Fe-Ni and sulphide minerals, alters major and trace element composition within the silicates.  Benoit, P.H. and Sears, D.W.G (1999) JGR. 14159-14168.  Hallis, L.J. (2013) MAPS. 1-15.  Steer, E.D. et al. (2014) LPSC Abstract #1958.
Testing the survival of microfossils in artificial martian sedimentary meteorites during entry into Earth?s atmosphere: the STONE 6 experimentElsevier, 2011-07-20Abstract If life ever appeared on Mars, could we find traces of primitive life embedded in sedimentary meteorites? To answer this question, a 3.5 billion-year-old volcanic sediment containing microfossils was embedded in the heat shield of a space capsule in order to test survival of the rock and the microfossils during entry into the Earth?s atmosphere (the STONE 6 experiment). The silicified volcanic sediment from the Kitty?s Gap Chert (Pilbara, Australia) is considered to be an excellent analogue for Noachian-age volcanic sediments. The microfossils in the chert are also analogues for potential martian life. An additional goal was to investigate the survival of living microorganisms (Chroococcidiopsis) protected by a 2 cm thick layer of rock in order to test whether living endolithic organisms could survive atmospheric entry when protected by a rocky coating. Mineralogical alteration of the sediment due to shock heating was manifested by the formation of a fusion crust, cracks in the chert due to prograde and retrograde changes of ? quartz to ? quartz, increase in the size of the fluid inclusions, and dewatering of the hydromuscovite-replaced volcanic protoliths. The carbonaceous microfossils embedded in the chert matrix survived in the rock away from the fusion crust but there was an increase in the maturity index of the kerogen towards the crust. We conclude that this kind of sediment can survive atmospheric entry and, if it contains microfossils, they could also survive. The living microorganisms were, however, completely carbonised by flame leakage to the back of the sample and therefore non-viable. However, using an analytical model to estimate the temperature reached within the sample thickness, we conclude that, even without flame leakage, the living organisms probably need to be protected by at least 5 cm of rock in order to be shielded from the intense heat of entry.
Meteorites, Mars and Beagle 2 - from novel analysis in the laboratory to pioneering experiments in spaceWright, I.P. (2003)On 25 December 2003, the British-built Beagle 2 probe will land on the surface of Mars to carry out one of the most potentially important pieces of analytical science ever conceived: to search for evidence of extra terrestrial life. Dr Ian Wright of the Open University talks us through the difficulties of performing measurements in such a harsh environment.