2016.66 9 25 17 hsi 10

Aaron J. Celestian

and 7 more

AbstractThe Getty Museum recently acquired the Borghese-Windsor Cabinet (Figure \ref{620486}), a piece of furniture extensively decorated with agate, lapis lazuli, and other semi-precious stones.  The cabinet is thought to have been built around 1620 for Camillo Borghese (later Pope Paul V).  The Sixtus Cabinet, built around 1585 for Pope Sixtus V (born Felice Peretti di Montalto), is of similar design to the Borghese-Windsor and also ornately decorated with gemstones.  Although there are similarities in gemstones between the two cabinets, the Sixtus and Borghese-Windsor cabinets vary in their agate content.  It was traditionally thought that all agate gemstones acquired during the 16th and 17th centuries were sourced from the Nahe River Valley near Idar-Oberstein, Germany.  It is known that Brazilian agate began to be imported into Germany by the 1800s, but it is possible that some was imported in the 18th century or earlier.  A primary research goal was to determine if the agates in the Borghese-Windsor Cabinet are of single origin, or if they have more than one geologic provenance. Agates are made of SiO2, mostly as the mineral quartz, but also as metastable moganite.  Both quartz and moganite will crystallize together as the agate forms, but moganite is not stable at Earth's surface and will convert to quartz over tens of millions of years \cite{Moxon_2004,Peter_J_Heaney_1995,G_slason_1997}, thus relatively older agate contains less moganite.  Agate from the Idar-Oberstein is Permian in age (around 280 million years old), while agate from Rio Grande do Sul of Brazil generally formed during the Cretaceous (around 120 million years old).  It is thought that Rio Grande do Sul would have been a primary source of material exported to Europe because it is one of Brazil's oldest and largest agate gemstone producers.  Since Cretaceous agate from Brazil is many millions of years younger than Permian agate from Germany, the quartz to moganite ratios between the two localities should be quite different.  The agate gemstones of the Borghese-Windsor Cabinet cannot be removed for detailed Raman mapping experiments.    Because of this, we first analyzed multiple agate specimens from the collections of the Natural History Museum of Los Angeles (NHMLA) and the Smithsonian Institution National Museum of Natural History (NMNH) using three different techniques: Raman mapping, XRF mapping, and hyperspectral imaging. Raman spectroscopy provides an easy method to distinguish the relative quartz:moganite ratios and XRF analysis provides a measure of bulk geochemistry in agates.  Maps have advantages over line scans and point analysis in that they give a better representation of the mineral content, can be used to exclude trace mineral impurities, and yield better counting statistics and averaging.   Hyperspectral imaging provides a range of optical data from IR through UV wavelengths.   
Mineral Sciences LaboratoryThe Mineral Sciences Laboratory is on public display as of November 2017.  All experimental stations, collections, and equipment are on view and scientific content is communicated to the visitor by signage, gallery interpreter engagement, video, and social media to our more than 800,000 physical visitors a year.  The Natural History Museum of Los Angeles County is located at 900 Exposition Blvd., Los Angeles. It is open daily 9:30 a .m. to 5 p .m. The Museum was the first dedicated museum building in Los Angeles, opening its doors in 1913. It has amassed one of the world’s most extensive and valuable collections of natural and cultural history — with more than 35 million objects, some as old as 4.5 billion years. The Natural History Family of Museums includes NHMLA, the La Brea Tar Pits and Museum (Hancock Park/Mid - Wilshire), and the William S. Hart Park and Museum (Newhall, California). The Family of Museums serves more than 1 million families and visitors annually and is a national leader in research, exhibitions, and education.  Raman MicroscopyThe Mineral Sciences Department is outfitted with a Horiba ExploRa+ dispersive Raman microscope.  Two lasers can be selected, a 532 nm and a 785 nm, with automated calibration for each laser using a silicon standard.  Typical Raman spectra for the 532 nm laser can be collected from 70 cm-1 to > 5000 cm-1, while the 785 nm laser spectral range is nominally from 80 cm-1 through 2500 cm-1.  Beam size at the sample is approximately 1.2 μm. Slits can be used to obtain better spectral resolution from a selection of 50 μm, 100 μm, 200 μm, and the microscopic can be used in confocal mode by selecting a pinhole, 100 μm, 200 μm, and 500 μm.  Laser power at the sample is adjustable, with a maximum of 15.2 mW (532 nm) at the sample.  Diffraction grating options are 600 gr/mm, 1200 gr/mm, 1800 gr/mm, and 2400 gr/mm, where the 1800 gr/mm is most commonly used.  A 10x (0.1 N.A.), 100x (0.9 N.A.), and 100x (0.7 N.A) long working distance objectives are available.  An automated XYZ stage controls sample positioning and mapping procedures. X-ray Fluorescence MicroscopeThe micro-XRF analyzer (Horiba XGT-7200) is used for single point, multi-point (user selected or line-scan), hyperspectral mapping analysis, and transmitted X-ray imaging.  The spatial resolution of the instrument is adjustable by means of computer-controlled switching between the 50 μm and 1.2 mm X-ray mono-capillary guide tube.  Dual vacuum modes (full and partial) allow for solid and liquid analysis.  Partial vacuum analysis keeps the sample at room pressure and the vacuum is applied to the detector and X-ray optics.  The elemental range is from Na to U, and Rh target is used with a maximum tube power at 50 kV and 1 mA.X-ray DiffractionSingle CrystalThe Rigaku R-Axis II is used to determine the atomic structure of crystals.  Crystals typically need to be less than 300 microns on edge, and larger than 5 microns on edge.  The R-Axis II also can do powder diffraction of single crystals or aggregates of crystals that would normally be too small for dedicated powder diffraction instruments.PowderThe Proto AXRD is a low power (600W, copper) X-ray powder diffractometer with a 6-sample autochanger.  The autochanger rotates the sample during data collection to help increase powder averaging statistics.  The AXRD is equipped with a Dectris Mythen linear detector.  Data from this instrument are used for mineral phase analysis as well as Rietveld refinement in some cases.  
Lpsc 2019 figure 1

Scott M. Perl

and 3 more

Introduction & Motivation Indications of extant or extinct life in the Martian shallow subsurface can be preserved alongside the evaporitic mineral record within sites where dried ancient lake systems are observed. Biological chemical markers (biomarkers) lose molecular stability over time, and detections of these over geologic time present challenges to biogenic validation. Agnostic biomarkers and the preservation of those in-situ molecules can be aided by biological feedback to ecological stresses that have been interpreted throughout the late Noachian/early Hesperian \cite{Ehlmann_2014,Murchie_2009}. Global desiccation and surface wide UV exposure are the major obstacles to in-situ biological preservation in the shallow crust \cite{Cockell_2000}. Burial of sedimentary material from early Hesperian aqueous sites can provide significant protection from these damaging effects. The purpose of this paper is to discuss the biological feedback from microbial communities preserved within Martian analogue mineralogy. Furthermore, we explore how biosignature preservation pathways can outlast the original biology in slow-changing evaporite mineral records. Geobiological Preservation & TerrestrialBiological Adaptation: Our continued focus is evaporating and dried terrestrial lake beds \cite{Baxter_2018} since that has proven to be ideal for modern and older biogenic preservation (Perl in prep. 2019). Mineral-microbe interactions can produce nutrients and sustained μm-scale environments where nutrient cycling and metabolic processes continue to produce useful proteins that combat ecological stresses found in measured OTUs from amplification of 16S rRNA (Figure \ref{461273}). Stated differently, molecular adaptations from surviving bacteria allow for later generations to better utilize their environments thereby showing significant similarities between ancient and younger prokaryotes \cite{Maughan_2002}. On Earth these similarities can yield to difficulty between relative age dating of bacteria and ruling out “modern” contamination of older mineral samples. Sedimentological relative dating of minerals can greatly assist with regard to preservation of biological material. However continued metabolic processes in preserved settings will lead to taxa differences (via neighbor joining clustering \cite{Saitou1987} when compared to the non-preserved environment. Hence, the need for proper  baseline environmental controls and understanding of contamination either from younger fluids or rock and mineral fracture. Early Peptide ChainsIf an independent origin of life on Mars and accompanying evolution pathways existed, the earliest evolved simple polypeptides may not have had the capacity for adaptation in the timeframe of climate change on Mars. Biochemically though, the very existence of these polypeptides may have been enough to provide feedback to ecological stresses. The timelines of C,H,O,N,P,S, a solvent (water), and environmental conditions overlapping would be the indicator of the duration of habitability. This duration would parallel the adaptability of organisms and the synthesis of more complex peptide chains leading to a greater ability to adapt to the changing Martian surface over geologic time.