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1.
Astrobiology ; 19(12): 1419-1432, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31424278

RESUMO

This report reviews how terrestrial hot spring systems can sustain diverse and abundant microbial communities and preserve their fossil records. Hot springs are dependable water sources, even in arid environments. They deliver reduced chemical species and other solutes to more oxidized surface environments, thereby providing redox energy and nutrients. Spring waters have diverse chemical compositions, and their outflows create thermal gradients and chemical precipitates that sustain diverse microbial communities and entomb their remnants. These environments probably were important habitats for ancient benthic microbial ecosystems, and it has even been postulated that life arose in hydrothermal systems. Thermal spring communities are fossilized in deposits of travertine, siliceous sinter, and iron minerals (among others) that are found throughout the geological record back to the oldest known well-preserved rocks at 3.48 Ga. Very few are known before the Cenozoic, but it is likely that there are many more to be found. They preserve fossils ranging from microbes to trees and macroscopic animals. Features on Mars whose morphological and spectroscopic attributes resemble spring deposits on Earth have been detected in regions where geologic context is consistent with the presence of thermal springs. Such features represent targets in the search for evidence of past life on that planet.

2.
Geobiology ; 17(2): 151-160, 2019 03.
Artigo em Inglês | MEDLINE | ID: mdl-30450841

RESUMO

Ooids are accretionary grains commonly reported from turbulent, shallow-water environments. They have long been associated with microbially dominated ecosystems and often occur in close proximity to, or embedded within, stromatolites, yet have historically been thought to form solely through physicochemical processes. Numerous studies have revealed both constructive and destructive roles for microbes colonizing the surfaces of modern calcitic and aragonitic ooids, but there has been little evidence for the operation of these processes during the Archean and Proterozoic, when both ooids and microbially dominated ecosystems were more widespread. Recently described carbonate ooids from the 2.9 Ga Pongola Supergroup, South Africa, include well-preserved examples composed of diagenetic dolomite interpreted to have formed from a high-Mg-calcite precursor. Spatial distributions of organic matter and elements associated with metabolic activity (N, S, and P) were interpreted as evidence for a biologically induced origin. Here, we describe exceptionally well-preserved ooids composed of calcite, collected from Earth's oldest known carbonate lake system, the ~2.72 Ga Meentheena Member (Tumbiana Formation), Fortescue Group, Western Australia. We used optical microscopy, Raman spectroscopy, XRD, SEM-EDS, LA-ICP-MS, EA-IRMS, and a novel micro-XRF instrument to investigate an oolite shoal deposited between stromatolites that preserve abundant evidence for microbial activity. We report an extremely fine, radial-concentric, calcitic microfabric that is similar to the primary and early diagenetic fabrics of calcitic ooids reported from modern temperate lakes. Early diagenetic silica has trapped isotopically light and thermally mature organic matter. The close association of organic matter with mineral phases and microfabrics related to primary and early diagenetic processes suggest incorporation of organic matter occurred during accretion, likely due to the presence of microbial biofilms. We conclude that the oldest known calcitic ooids were likely formed through processes similar to those that mediate the accretion of ooids in similar environments today, including formation within a microbial biosphere.


Assuntos
Fenômenos Fisiológicos Bacterianos , Biofilmes , Carbonato de Cálcio/análise , Carbonatos/análise , Sedimentos Geológicos/química , Lagos/química , Paleontologia , Austrália Ocidental
3.
Nat Commun ; 8: 16149, 2017 08 16.
Artigo em Inglês | MEDLINE | ID: mdl-28812546

RESUMO

This corrects the article DOI: 10.1038/ncomms15263.

4.
Nat Commun ; 8: 15263, 2017 05 09.
Artigo em Inglês | MEDLINE | ID: mdl-28486437

RESUMO

The ca. 3.48 Ga Dresser Formation, Pilbara Craton, Western Australia, is well known for hosting some of Earth's earliest convincing evidence of life (stromatolites, fractionated sulfur/carbon isotopes, microfossils) within a dynamic, low-eruptive volcanic caldera affected by voluminous hydrothermal fluid circulation. However, missing from the caldera model were surface manifestations of the volcanic-hydrothermal system (hot springs, geysers) and their unequivocal link with life. Here we present new discoveries of hot spring deposits including geyserite, sinter terracettes and mineralized remnants of hot spring pools/vents, all of which preserve a suite of microbial biosignatures indicative of the earliest life on land. These include stromatolites, newly observed microbial palisade fabric and gas bubbles preserved in inferred mineralized, exopolymeric substance. These findings extend the known geological record of inhabited terrestrial hot springs on Earth by ∼3 billion years and offer an analogue in the search for potential fossil life in ancient Martian hot springs.

5.
Appl Environ Microbiol ; 83(13)2017 07 01.
Artigo em Inglês | MEDLINE | ID: mdl-28455341

RESUMO

To investigate the function of 2-methylhopanoids in modern cyanobacteria, the hpnP gene coding for the radical S-adenosyl methionine (SAM) methylase protein that acts on the C-2 position of hopanoids was deleted from the filamentous cyanobacterium Nostoc punctiforme ATCC 29133S. The resulting ΔhpnP mutant lacked all 2-methylhopanoids but was found to produce much higher levels of two bacteriohopanepentol isomers than the wild type. Growth rates of the ΔhpnP mutant cultures were not significantly different from those of the wild type under standard growth conditions. Akinete formation was also not impeded by the absence of 2-methylhopanoids. The relative abundances of the different hopanoid structures in akinete-dominated cultures of the wild-type and ΔhpnP mutant strains were similar to those of vegetative cell-dominated cultures. However, the ΔhpnP mutant was found to have decreased growth rates under both pH and osmotic stress, confirming a role for 2-methylhopanoids in stress tolerance. Evidence of elevated photosystem II yield and NAD(P)H-dependent oxidoreductase activity in the ΔhpnP mutant under stress conditions, compared to the wild type, suggested that the absence of 2-methylhopanoids increases cellular metabolic rates under stress conditions.IMPORTANCE As the first group of organisms to develop oxygenic photosynthesis, Cyanobacteria are central to the evolutionary history of life on Earth and the subsequent oxygenation of the atmosphere. To investigate the origin of cyanobacteria and the emergence of oxygenic photosynthesis, geobiologists use biomarkers, the remnants of lipids produced by different organisms that are found in geologic sediments. 2-Methylhopanes have been considered indicative of cyanobacteria in some environmental settings, with the parent lipids 2-methylhopanoids being present in many contemporary cyanobacteria. We have created a Nostoc punctiforme ΔhpnP mutant strain that does not produce 2-methylhopanoids to assess the influence of 2-methylhopanoids on stress tolerance. Increased metabolic activity in the mutant under stress indicates compensatory alterations in metabolism in the absence of 2-methylhopanoids.


Assuntos
Nostoc/metabolismo , Triterpenos/metabolismo , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Concentração de Íons de Hidrogênio , Isomerismo , Metilação , Nostoc/química , Nostoc/genética , Nostoc/crescimento & desenvolvimento , Osmose , Triterpenos/química
7.
Proc Natl Acad Sci U S A ; 112(7): 2087-92, 2015 Feb 17.
Artigo em Inglês | MEDLINE | ID: mdl-25646436

RESUMO

The recent discovery of a deep-water sulfur-cycling microbial biota in the ∼ 2.3-Ga Western Australian Turee Creek Group opened a new window to life's early history. We now report a second such subseafloor-inhabiting community from the Western Australian ∼ 1.8-Ga Duck Creek Formation. Permineralized in cherts formed during and soon after the 2.4- to 2.2-Ga "Great Oxidation Event," these two biotas may evidence an opportunistic response to the mid-Precambrian increase of environmental oxygen that resulted in increased production of metabolically useable sulfate and nitrate. The marked similarity of microbial morphology, habitat, and organization of these fossil communities to their modern counterparts documents exceptionally slow (hypobradytelic) change that, if paralleled by their molecular biology, would evidence extreme evolutionary stasis.


Assuntos
Bactérias/isolamento & purificação , Evolução Biológica , Fósseis/microbiologia , Enxofre/metabolismo , Bactérias/metabolismo
8.
Environ Microbiol ; 15(5): 1464-75, 2013 May.
Artigo em Inglês | MEDLINE | ID: mdl-22712472

RESUMO

Families of closely related chemical compounds, which are relatively resistant to degradation, are often used as biomarkers to help trace the evolutionary history of early groups of organisms and the environments in which they lived. Biomarkers derived from hopanoid variations are particularly useful in determining bacterial community compositions. 2-Methylhopananoids have been thought to be diagnostic for cyanobacteria, and 2-methylhopanes in the geological record are taken as evidence for the presence of cyanobacteria-containing communities at the time of sediment deposition. Recently, however, doubt has been cast on the validity of 2-methylhopanes as cyanobacterial biomarkers, since non-cyanobacterial species have been shown to produce significant amounts of 2-methylhopanoids. This study examines the diversity of hpnP, the hopanoid biosynthesis gene coding for the enzyme that methylates hopanoids at the C2 position. Genomic DNA isolated from stromatolite-associated pustular and smooth microbial mat samples from Shark Bay, Western Australia, was analysed for bacterial diversity, and used to construct an hpnP clone library. A total of 117 partial hpnP clones were sequenced, representing 12 operational taxonomic units (OTUs). Phylogenetic analysis showed that 11 of these OTUs, representing 115 sequences, cluster within the cyanobacterial clade. We conclude that the dominant types of microorganisms with the detected capability of producing 2-methylhopanoids within pustular and smooth microbial mats in Shark Bay are cyanobacteria.


Assuntos
Baías/microbiologia , Biomarcadores/análise , Cianobactérias/genética , Variação Genética , Sequência de Aminoácidos , Cianobactérias/classificação , Cianobactérias/isolamento & purificação , Primers do DNA/genética , Biblioteca Gênica , Dados de Sequência Molecular , Filogenia , Metiltransferases de Proteína/genética , RNA Ribossômico 16S/genética , Alinhamento de Sequência , Austrália Ocidental
9.
Astrobiology ; 12(12): 1143-53, 2012 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-23134090

RESUMO

There is concern in many developed countries that school students are turning away from science. However, students may be choosing not to study science and dismissing the possibility of a scientific career because, in the junior secondary years, they gain a false view of science and the work of scientists. There is a disparity between science as it is portrayed at school and science as it is practiced. This paper describes a study to explore whether engaging in science through astrobiology outreach activities may improve students' understanding of the nature and processes of science, and how this may influence their interest in a career in science. The results suggest that the students attending these Mars research-related outreach activities are more interested in science than the average student but are lacking in understanding of aspects of the nature of science. A significant difference was detected between pre- and posttest understandings of some concepts of the nature of science.


Assuntos
Exobiologia/educação , Ciência/educação , Criatividade , Humanos , Marte , Pesquisa/educação , Estudantes
10.
Astrobiology ; 10(9): 899-920, 2010 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-21118023

RESUMO

Morphologically diverse structures that may constitute organic microfossils are reported from three remote and widely separated localities assigned to the ca. 3400 Ma Strelley Pool Formation in the Pilbara Craton, Western Australia. These localities include the Panorama, Warralong, and Goldsworthy greenstone belts. From the Panorama greenstone belt, large (> 40 µm) lenticular to spindle-like structures, spheroidal structures, and mat-forming thread-like structures are found. Similar assemblages of carbonaceous structures have been identified from the Warralong and Goldsworthy greenstone belts, though these assemblages lack the thread-like structures but contain film-like structures. All structures are syngenetic with their host sedimentary black chert, which is associated with stromatolites and evaporites. The host chert is considered to have been deposited in a shallow water environment. Rigorous assessment of biogenicity (considering composition, size range, abundance, taphonomic features, and spatial distributions) suggests that cluster-forming small (<15 µm) spheroids, lenticular to spindle-like structures, and film-like structures with small spheroids are probable microfossils. Thread-like structures are more likely fossilized fibrils of biofilm, rather than microfossils. The biogenicity of solitary large (>15 µm) spheroids and simple film-like structures is less certain. Although further investigations are required to confirm the biogenicity of carbonaceous structures from the Strelley Pool Formation, this study presents evidence for the existence of morphologically complex and large microfossils at 3400 Ma in the Pilbara Craton, which can be correlated to the contemporaneous, possible microfossils reported from South Africa. Although there is still much to be learned, they should provide us with new insights into the early evolution of life and shallow water ecosystems.


Assuntos
Fósseis , Sedimentos Geológicos/química , Evolução Biológica , Ecossistema , Meteoroides , Origem da Vida , África do Sul , Austrália Ocidental
11.
Astrobiology ; 10(4): 413-24, 2010 May.
Artigo em Inglês | MEDLINE | ID: mdl-20528196

RESUMO

The origin of organic microstructures in the approximately 3 Ga Farrel Quartzite is controversial due to their relatively poor state of preservation, the Archean age of the cherts in which they occur, and the unusual spindle-like morphology of some of the forms. To provide more insight into the significance of these microstructures, nano-scale secondary ion mass spectrometry (NanoSIMS) maps of carbon, nitrogen, sulfur, silicon, and oxygen were obtained for spheroidal and spindle-shaped constituents of the Farrel Quartzite assemblage. Results suggest that the structures are all bona fide approximately 3 Ga microfossils. The spindles demonstrate an architecture that is remarkable for 3 Ga organisms. They are relatively large, robust, and morphologically complex. The NanoSIMS element maps corroborate their complexity by demonstrating an intricate, internal network of organic material that fills many of the spindles and extends continuously from the body of these structures into their spearlike appendages. Results from this study combine with previous morphological and chemical analyses to argue that the microstructures in the Farrel Quartzite comprise a diverse assemblage of Archean microfossils. This conclusion adds to a growing body of geochemical, stromatolitic, and morphological evidence that indicates the Archean biosphere was varied and well established by at least approximately 3 Ga. Together, the data paint a picture of Archean evolution that is one of early development of morphological and chemical complexity. The evidence for Archean evolutionary innovation may augur well for the possibility that primitive life on other planets could adapt to adverse conditions by ready development of diversity in form and biochemistry.


Assuntos
Biodiversidade , Ecossistema , Fósseis , Nanoestruturas/química , Espectrometria de Massa de Íon Secundário/métodos , Nanotecnologia , Fatores de Tempo , Austrália Ocidental
12.
J Proteome Res ; 8(5): 2218-25, 2009 May.
Artigo em Inglês | MEDLINE | ID: mdl-19206189

RESUMO

Responses to changes in external salinity were examined in Halobacterium salinarum NRC-1. H. salinarum NRC-1 grows optimally at 4.3 M NaCl and is capable of growth between 2.6 and 5.1 M NaCl. Physiological changes following incubation at 2.6 M NaCl were investigated with respect to growth behavior and proteomic changes. Initial observations indicated delayed growth at low NaCl concentrations (2.6 M NaCl), and supplementation with different sugars, amino acids, or KCl to increase external osmotic pressure did not reverse these growth perturbations. To gain a more detailed insight into the adaptive responses of H. salinarum NRC-1 to changes in salinity, the proteome was characterized using iTRAQ (amine specific isobaric tagging reagents). Three hundred and nine differentially expressed proteins were shown to be associated with changes in the external sodium chloride concentration, with proteins associated with metabolism revealing the greatest response.


Assuntos
Proteínas Arqueais/análise , Halobacterium salinarum/efeitos dos fármacos , Proteoma/análise , Proteômica/métodos , Cloreto de Sódio/farmacologia , Proteínas Arqueais/classificação , Proteínas Arqueais/metabolismo , Cromatografia Líquida/métodos , Relação Dose-Resposta a Droga , Halobacterium salinarum/crescimento & desenvolvimento , Halobacterium salinarum/metabolismo , Espectrometria de Massas/métodos , Proteoma/classificação , Proteoma/metabolismo , Fatores de Tempo
13.
Int J Mol Sci ; 9(12): 2622-38, 2008 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-19330097

RESUMO

QDs may offer significant advantages in environmental and bead-based applications where the target cells need to be discriminated above background fluorescence. We have examined the possible applications of QDs for flow cytometric measurements (FCM) by studying their excitation - emission spectra and their binding to paramagnetic beads. We labelled beads with either QDs or a commonly-used fluorochrome (FITC) and studied their fluorescence intensity by FCM. Flow cytometric comparisons indicated that the minimum fluorophore concentration required for detection of QDs above autofluorescent background was 100-fold less than for FITC.

14.
Astrobiology ; 7(4): 631-43, 2007 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-17723094

RESUMO

Recently, halite and sulfate evaporate rocks have been discovered on Mars by the NASA rovers, Spirit and Opportunity. It is reasonable to propose that halophilic microorganisms could have potentially flourished in these settings. If so, biomolecules found in microorganisms adapted to high salinity and basic pH environments on Earth may be reliable biomarkers for detecting life on Mars. Therefore, we investigated the potential of Resonance Raman (RR) spectroscopy to detect biomarkers derived from microorganisms adapted to hypersaline environments. RR spectra were acquired using 488.0 and 514.5 nm excitation from a variety of halophilic archaea, including Halobacterium salinarum NRC-1, Halococcus morrhuae, and Natrinema pallidum. It was clearly demonstrated that RR spectra enhance the chromophore carotenoid molecules in the cell membrane with respect to the various protein and lipid cellular components. RR spectra acquired from all halophilic archaea investigated contained major features at approximately 1000, 1152, and 1505 cm(-1). The bands at 1505 cm(-1) and 1152 cm(-1) are due to in-phase C=C (nu(1) ) and C-C stretching ( nu(2) ) vibrations of the polyene chain in carotenoids. Additionally, in-plane rocking modes of CH(3) groups attached to the polyene chain coupled with C-C bonds occur in the 1000 cm(-1) region. We also investigated the RR spectral differences between bacterioruberin and bacteriorhodopsin as another potential biomarker for hypersaline environments. By comparison, the RR spectrum acquired from bacteriorhodopsin is much more complex and contains modes that can be divided into four groups: the C=C stretches (1600-1500 cm(-1)), the CCH in-plane rocks (1400-1250 cm(-1)), the C-C stretches (1250-1100 cm(-1)), and the hydrogen out-of-plane wags (1000-700 cm(-1)). RR spectroscopy was shown to be a useful tool for the analysis and remote in situ detection of carotenoids from halophilic archaea without the need for large sample sizes and complicated extractions, which are required by analytical techniques such as high performance liquid chromatography and mass spectrometry.


Assuntos
Exobiologia , Halobacteriales/isolamento & purificação , Halobacterium salinarum/isolamento & purificação , Carotenoides/análise , Cromatografia Líquida de Alta Pressão , Halobacteriales/química , Halobacteriales/crescimento & desenvolvimento , Halobacterium salinarum/química , Halobacterium salinarum/crescimento & desenvolvimento , Marte , Espectrometria de Massas , Análise Espectral Raman/métodos , Estados Unidos , United States National Aeronautics and Space Administration , beta Caroteno/análise
15.
Nature ; 441(7094): 714-8, 2006 Jun 08.
Artigo em Inglês | MEDLINE | ID: mdl-16760969

RESUMO

The 3,430-million-year-old Strelley Pool Chert (SPC) (Pilbara Craton, Australia) is a sedimentary rock formation containing laminated structures of probable biological origin (stromatolites). Determining the biogenicity of such ancient fossils is the subject of ongoing debate. However, many obstacles to interpretation of the fossils are overcome in the SPC because of the broad extent, excellent preservation and morphological variety of its stromatolitic outcrops--which provide comprehensive palaeontological information on a scale exceeding other rocks of such age. Here we present a multi-kilometre-scale palaeontological and palaeoenvironmental study of the SPC, in which we identify seven stromatolite morphotypes--many previously undiscovered--in different parts of a peritidal carbonate platform. We undertake the first morphotype-specific analysis of the structures within their palaeoenvironment and refute contemporary abiogenic hypotheses for their formation. Finally, we argue that the diversity, complexity and environmental associations of the stromatolites describe patterns that--in similar settings throughout Earth's history--reflect the presence of organisms.


Assuntos
Fósseis , Sedimentos Geológicos/microbiologia , Modelos Biológicos , Austrália , Carbonatos/química , Sedimentos Geológicos/química , História Antiga , Paleontologia , Água do Mar , Fatores de Tempo
16.
17.
Nature ; 423(6940): 632-5, 2003 Jun 05.
Artigo em Inglês | MEDLINE | ID: mdl-12789336

RESUMO

Many independent lines of evidence document a large increase in the Earth's surface oxidation state 2,400 to 2,200 million years ago, and a second biospheric oxygenation 800 to 580 million years ago, just before large animals appear in the fossil record. Such a two-staged oxidation implies a unique ocean chemistry for much of the Proterozoic eon, which would have been neither completely anoxic and iron-rich as hypothesized for Archaean seas, nor fully oxic as supposed for most of the Phanerozoic eon. The redox chemistry of Proterozoic oceans has important implications for evolution, but empirical constraints on competing environmental models are scarce. Here we present an analysis of the iron chemistry of shales deposited in the marine Roper Basin, Australia, between about 1,500 and 1,400 million years ago, which record deep-water anoxia beneath oxidized surface water. The sulphur isotopic compositions of pyrites in the shales show strong variations along a palaeodepth gradient, indicating low sulphate concentrations in mid-Proterozoic oceans. Our data help to integrate a growing body of evidence favouring a long-lived intermediate state of the oceans, generated by the early Proterozoic oxygen revolution and terminated by the environmental transformation late in the Proterozoic eon.


Assuntos
Fósseis , Sedimentos Geológicos/química , Hipóxia , Oxigênio/análise , Água do Mar/química , Sulfatos/análise , Austrália , Carbonatos/análise , Ferro/análise , Isótopos , Biologia Marinha , Oceanos e Mares , Oxirredução , Sulfetos/análise
18.
Astrobiology ; 2(3): 255-70, 2002.
Artigo em Inglês | MEDLINE | ID: mdl-12530236

RESUMO

Paralana is an active, radon-containing hot spring situated in a region of South Australia's Flinders Ranges with a long history of hydrothermal activity. Our aim was to determine the bacterial composition of Paralana using a culture-independent, 16S rRNA-based technique. The presence of a diverse bacterial community was strongly suggested by the large number (approximately 180) of different ribotypes obtained upon analysis of nine hot spring samples. DNA sequencing of Paralana 16S rRNA genes corroborated this observation, identifying representatives of seven confirmed and two candidate divisions of the domain Bacteria. These included Cyanobacteria, Proteobacteria (both beta and delta subdivisions), the Cytophaga-Flexibacter-Bacteroides group, Low G + C Gram-positives, Nitrospira, green non-sulfur bacteria, green sulfur bacteria, OP8, and OP12. No known ionizing radiation-resistant Bacteria were identified. Only one Paralana 16S rRNA sequence type (recombinant B5D) was homologous to a sequence previously identified from a radioactive environment.


Assuntos
Bactérias/isolamento & purificação , Radônio , Microbiologia da Água , Bactérias/classificação , Bactérias/genética , Sequência de Bases , Primers do DNA , RNA Ribossômico 16S/genética , Austrália do Sul
19.
Astrobiology ; 2(3): 335-51, 2002.
Artigo em Inglês | MEDLINE | ID: mdl-12530243

RESUMO

An integrated analysis of both airborne and field short-wave infrared hyperspectral measurements was used in conjunction with conventional field mapping techniques to map hydrothermal alteration in the central portion of the Mount Painter Inlier in the Flinders Ranges, South Australia. The airborne hyperspectral data show the spatial distribution of spectrally distinct minerals occurring as primary minerals and as weathering and alteration products. Field spectral measurements, taken with a portable infrared mineral analyzer spectrometer and supported by thin-section analyses, were used to verify the mineral maps and enhance the level of information obtainable from the airborne data. Hydrothermal alteration zones were identified and mapped separately from the background weathering signals. A main zone of alteration, coinciding with the Paralana Fault zone, was recognized, and found to contain kaolinite, muscovite, biotite, and K-feldspar. A small spectral variation associated with a ring-like feature around Mount Painter was tentatively determined to be halloysite and interpreted to represent a separate hydrothermal fluid and fluid source, and probably a separate system. The older parts of the alteration system are tentatively dated as Permo-Carboniferous. The remote sensing of alteration at Mount Painter confirms that hyperspectral imaging techniques can produce accurate mineralogical maps with significant details that can be used to identify and map hydrothermal activity. Application of hyperspectral surveys such as that conducted at Mount Painter would be likely to provide similar detail about putative hydrothermal deposits on Mars.


Assuntos
Marte , Espectrofotometria Infravermelho , Fenômenos Geológicos , Geologia
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