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All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Looking for Fossil Bacteria in Martian Materials

The rationale for looking for prokaryote fossils in Martian materials is based on our present understanding of the environmental evolution of that planet in comparison to the history of the terrestrial environments and the development and evolution of life on Earth. On Earth we have clear, albeit indirect, evidence of life in 3.8 b.y.-old rocks from Greenland and the first morphological fossils in 3.3-3.5 b.y.-old cherts from South Africa and Australia. In comparison, Mars, being smaller, probably cooled down after initial aggregation faster than the Earth. Consequently, there could have been liquid water on its surface earlier than on Earth. With a similar exogenous and endogenous input of organics and life-sustaining nutrients as is proposed for the Earth, life could have arisen on that planet, possibly slightly earlier dm it did on Earth. Whereas on Earth liquid water has remained at the surface of the planet since about 4.4 b.y. (with some possible interregnums caused by planet-sterilising impacts before 3.8. b.y. and perhaps a number of periods of a totally frozen Earth, this was not the case with Mars. Although it is not known exactly when surficial water disappeared from the surface, there would have been sufficient time for life to have developed into something similar to the terrestrial prokaryote stage. However, given the earlier environmental deterioration, it is unlikely that it evolved into the eukaryote stage and even evolution of oxygenic photosynthesis may not have been reached. Thus, the impetus of research is on single celled life simnilar to prokaryotes. We are investigating a number of methods of trace element analysis with respect to the Early Archaean microbial fossils. Preliminary neutron activation analysis of carbonaceous layers in the Early Archaean cherts from South Africa and Australia shows some partitioning of elements such as As, Sb, Cr with an especial enrichment of lanthanides in a carbonaceous-rich banded iron sediment . More significantly, preliminary TOF-SIMS investigations of organics in the cherts reveals the presence of a biomarker, which appears to be a derivative of bacterial polymer, in the carbonaceous parts of the rocks. We conclude that a combination of morphological, isotope and biogeochemical methods can be used to successfully identify signs of life in terrestrial material, and that these methods will be useful in searching for signs of life in extraterrestrial materials.

Westall, F.↗
NASA NTRS1995

Fossilization Processes in Thermal Springs

To create a comparative framework for the study of ancient examples, we have been carrying out parallel studies of the microbial biosedimentology, taphonomy and geochemistry of modem and sub-Recent thermal spring deposits. One goal of the research is the development of integrated litho- and taphofacies models for siliceous and travertline sinters. Thermal springs are regarded as important environments for the origin and early evolution of life on Earth, and we seek to utilize information from the fossil record to reconstruct the evolution of high temperature ecosystems. Microbial contributions to the fabric of thermal spring sinters occur when population growth rates keep pace with, or exceed rates of inorganic precipitation, allowing for the development of continuous biofilms or mats. In siliceous thermal springs, microorganisms are typically entombed while viable. Modes of preservation reflect the balance between rates of organic matter degradation, silica precipitation and secondary infilling. Subaerial sinters are initially quite porous and permeable and at temperatures higher than about 20 C, organic materials are usually degraded prior to secondary infilling of sinter frameworks. Thus, organically-preserved microfossils are rare and fossil information consists of characteristic biofabrics formed by the encrustation and underplating of microbial mat surfaces. This probably accounts for the typically low total organic carbon values observed in thermal spring deposits. In mid-temperature, (approx. 35 - 59 C) ponds and outflows, the surface morphology of tufted Phormidium mats is preserved through mat underplating by thin siliceous: crusts. Microbial taxes lead to clumping of ceils and/or preferred filament orientations that together define higher order composite fabrics in thermal spring stromatolites (e.g. network, coniform, and palisade). At lower temperatures (less than 35 C), Calothrix mats cover shallow terracette pools forming flat carpets or pustular surfaces that produce palisade and "shrub" fabrics, respectively. At finer scales, composite fabrics are seen to consist distinctive associations of microstructures formed by the encrustation of individual cells and filaments. Composite fabrics survive the diagenetic transitions from primary opaline silica to quartz and are known from subaerial thermal spring deposits as old as Lower Carboniferous. However, fossil microorganisms tend to be rare in older deposits, and are usually preserved only where cells or sheaths have been stained by iron oxides. In subaqueous mineralizing springs at lower temperatures, early infilling leads to a more rapid and complete reduction in porosity and permeability. This process, along with the slower rates of microbial degradation at lower temperatures, creates a more favorable situation for organic matter preservation. Application of this taphonomic model to the Rhynie Chert, previously interpreted as subaerial, suggest it was probably deposited in a subaqueous spring setting at lower temperatures.

Farmer, Jack D.↗
NASA NTRS1997

Fossilization of Coniform (Phormidium) Stromatolites In Siliceous Thermal Springs, Yellowstone National Park

We have studied fossilization processes in well-developed cyanobacterial mats present in mid-terrace ponds of silica-precipitating thermal springs of Yellowstone National Park. These mats occur over temperatures of approx.35-60 C and are dominated by species of Phormidium. Within Bonded systems two end member environments have been distinguished based temperature, depth, and the stability of spring inflows, each differing substantially in the style of stromatolite morphogenesis and fossilization. Type 1 systems include shallow, ephemeral ponds where water flow and temperature fluctuates widely on a seasonal basis; mats typically secrete rapidly up to the air-water interface, forming exposed islands. Silicification occurs primarily by the wicking of water onto the surface of exposed mats, leading to the evaporative concentration of silica near the surface. pH microelectronic measurements in partially-exposed columns show strong gradients in pH with values exceeding 10.5 in the upper am of silicifying mats, decreasing to <9.0 a few mm below the surface. High oxygen concentrations lead to the rapid oxidation of most organic materials. In Type I systems, the tops of coniform and columnar stromatolites become silicified first, followed by the bases. This typically leads to extensive fragmentation during the initial stages of burial. Case 2 systems include deeper ponds where the water flow, temperature and depth are seasonally more stable, and where mats develop larger-scale tufts and columns. Alkalinity in permanently submerged mats increases into tuft interiors from approx.9.0 near the surface to >10.0 at depth. Moderate silicification is apparent throughout mat frameworks, although there is frequently a densely silicified core near the base. In Type 2 systems, preservation of the coniform and columnar architecture of stromatoilites is much more robust. Sub-fossil examples suggest minimal fragmentation prior to burial. Comparative rapid analysis of the phone zones of submerged and exposed (silicifying) mats demonstrated the recovery of comparable levels of esterified fatty acids in both types of mats. Membrane lipids apparently remain intact during the early stages of silicification, although their fate during early diagenesis is still being evaluated.

Farmer, Jack↗
NASA NTRS2004

Fossil Signatures Using Elemental Abundance Distributions and Bayesian Probabilistic Classification

Elemental abundances (C6, N7, O8, Na11, Mg12, Al3, P15, S16, Cl17, K19, Ca20, Ti22, Mn25, Fe26, and Ni28) were obtained for a set of terrestrial fossils and the rock matrix surrounding them. Principal Component Analysis extracted five factors accounting for the 92.5% of the data variance, i.e. information content, of the elemental abundance data. Hierarchical Cluster Analysis provided unsupervised sample classification distinguishing fossil from matrix samples on the basis of either raw abundances or PCA input that agreed strongly with visual classification. A stochastic, non-linear Artificial Neural Network produced a Bayesian probability of correct sample classification. The results provide a quantitative probabilistic methodology for discriminating terrestrial fossils from the surrounding rock matrix using chemical information. To demonstrate the applicability of these techniques to the assessment of meteoritic samples or in situ extraterrestrial exploration, we present preliminary data on samples of the Orgueil meteorite. In both systems an elemental signature produces target classification decisions remarkably consistent with morphological classification by a human expert using only structural (visual) information. We discuss the possibility of implementing a complexity analysis metric capable of automating certain image analysis and pattern recognition abilities of the human eye using low magnification optical microscopy images and discuss the extension of this technique across multiple scales.

Hoover, Richard B.↗
NASA NTRS2021

Reductions in NO2 Burden Over North Equatorial Africa from Decline in Biomass Burning in Spite of Growing Fossil Fuel Use, 2005 to 2017

Socioeconomic development in low- and middle-income countries has been accompanied by increased emissions of air pollutants, such as nitrogen oxides [NOx: nitrogen dioxide (NO2) + nitric oxide (NO)], which affect human health. In sub-Saharan Africa, fossil fuel combustion has nearly doubled since 2000. At the same time, landscape biomass burning—another important NOx source—has declined in north equatorial Africa, attributed to changes in climate and anthropogenic fire management. Here, we use satellite observations of tropospheric NO2 vertical column densities (VCDs) and burned area to identify NO2 trends and drivers over Africa. Across the northern ecosystems where biomass burning occurs—home to hundreds of millions of people—mean annual tropospheric NO2 VCDs decreased by 4.5% from 2005 through 2017 during the dry season of November through February. Reductions in burned area explained the majority of variation in NO2 VCDs, though changes in fossil fuel emissions also explained some variation. Over Africa’s biomass burning regions, raising mean GDP density (USD·km−2) above its lowest levels is associated with lower NO2 VCDs during the dry season, suggesting that economic development mitigates net NO2 emissions during these highly polluted months. In contrast to the traditional notion that socioeconomic development increases air pollutant concentrations in low- and middle-income nations, our results suggest that countries in Africa’s northern biomass-burning region are following a different pathway during the fire season, resulting in potential air quality benefits. However, these benefits may be lost with increasing fossil fuel use and are absent during the rainy season.

air pollution↗
NASA NTRS2019

Exploiting OMI NO2 Satellite Observations to Infer Fossil-fuel CO2 Emissions from U.S. Megacities

Fossil-fuel CO2 emissions and their trends in eight U.S. megacities during 2006–2017 are inferred by combining satellite-derived NOX emissions with bottom-up city-specific NOX-to-CO2 emission ratios. A statistical model is fit to a collection NO2 plumes observed from the Ozone Monitoring Instrument (OMI), and is used to calculate top-down NOX emissions. Decreases in OMI-derived NOX emissions are observed across the eight cities from 2006 to 2017 (−17% in Miami to −58% in Los Angeles), and are generally consistent with long-term trends of bottom-up inventories (−25% in Miami to −49% in Los Angeles), but there are some interannual discrepancies. City-specific NOX-to-CO2 emission ratios, used to calculate inferred CO2, are estimated through annual bottom-up inventories of NOX and CO2 emissions disaggregated to 1 × 1 km2 resolution. Over the study period, NOX-to-CO2 emission ratios have decreased by ~40% nationwide (−24% to −51% for our studied cities), which is attributed to a faster reduction in NOX when compared to CO2 due to policy regulations and fuel type shifts. Combining top-down NOX emissions and bottom-up NOX-to-CO2 emission ratios, annual fossil-fuel CO2 emissions are derived. Inferred OMI-based top-down CO2 emissions trends vary between +7% in Dallas to −31% in Phoenix. For 2017, we report annual fossil-fuel CO2 emissions to be: Los Angeles 113 ± 49 Tg/yr; New York City 144 ± 62 Tg/yr; and Chicago 55 ± 24 Tg/yr. A study in the Los Angeles area, using independent methods, reported a 2013–2016 average CO2 emissions rate of 104 Tg/yr and 120 Tg/yr, which suggests that the CO2 emissions from our method are in good agreement with other studies' top-down estimates. We anticipate future remote sensing instruments – with better spatial and temporal resolution – will better constrain the NOX-to-CO2 ratio and reduce the uncertainty in our method.

Ozone Monitoring Instrument (OMI)↗
NASA NTRSDate not supplied

Biomass Burning and Fossil Fuel Apportionment via Greenhouse Gas Enhancement Ratios Over Southeast Asia as Measured During ASIA-AQ

As Southeast Asian economies continue to grow, so will their contribution to global greenhouse gas (GHG) emissions, driven primarily by increases in fossil fuel combustion. Left unchecked, these emissions will negatively impact air quality and climate, therefore it is imperative that emission sources are properly identified and accounted for in emission inventories. Enhancement ratios of GHGs have been used to characterize regional emissions as either dominated by fossil fuel combustion or biomass burning. In particular, airborne assessment of short-term continuous emission ratios has proven useful to quantify relative contributions of fossil fuel and biomass burning to GHG emissions. The 2024 Airborne and Satellite Investigation of Asian Air Quality (ASIA-AQ) campaign, flying over the Philippines, Korea, Thailand, and Taiwan, sampled a variety of emissions including significant biomass burning, local urban pollution, and transport events. This work will explore the impact of GHG emissions on the distinctive pollution of the sampled locations. As airborne GHG measurements over Southeast Asia are scarce if not nonexistent, this work provides a crucial link between established ground-based measurements and state-of-the-art satellite observations such as those from South Korea’s Geostationary Environment Monitoring Spectrometer (GEMS). Analysis of GHG enhancement ratios in East Asia will lead to more accurate emission inventories which can be used to implement more effective GHG control measures leading to improved air quality and minimizing the effect on climate.

ASIA-AQ↗
NASA NTRS1990

Shell structure and distribution of Cloudina, a potential index fossil for the terminal Proterozoic

Cloudina-bearing biosparites and biomicrites in the lower part of the Nama Group, Namibia, contain a wide morphological diversity of shell fragments that can all be attributed to the two named species C. hartmannae and C. riemkeae. The curved to sinuous tubular shells of Cloudina were multi-layered. Each shell layer was 8 to 50 micrometers thick and in the form of a slightly flaring tube with one end open and the other closed. Growth appears to have been periodic with successive shell layers forming within older layers. Each added layer was slightly elevated from the previous layer at the proximal end and was asymmetrically placed within the older layer so that only a portion of the new shell layer was fused to the previous layer. This type of growth left a relatively large unminerialized area between the shell layers which was often partially or fully occluded by early marine cements. The thin shell layers exhibit both plastic and brittle deformation and were likely formed of a rigid CaCO3-impregnated organic-rich material. Often the shell layers are preferentially dolomitized suggesting an original mineralogy of high-magnesian calcite. Both species in the Nama Group formed thickets, or perhaps bioherms, and this sedentary and gregarious habit suggests that Cloudina was probably a filter-feeding metazoan of at least a cnidarian grade of organization. The unusual shell structure of Cloudina gives rise to a characteristic suite of taphonomic and diagenetic features that can be used to identify Cloudina-bearing deposits within the Nama Group and in other terminal Proterozoic deposits around the world. Species of Cloudina occur in limestones from Brazil, Spain, China, and Oman in sequences consistent with a latest Proterozoic age assignment. In addition, supposed lower Cambrian, pre-trilobitic, shelly fossils from northwest Mexico and the White-Inyo Mountains in California and Nevada, including Sinotubulites, Nevadatubulus, and Wyattia, are all either closely related to or con-generic with Cloudina. Hence, it is probable that these outcrops are latest Proterozoic in age, and that Cloudina or Cloudina-like organisms were widely distributed at that time. It is possible, moreover, to suggest that metazoan biomineralization occurred on a global scale by the latest Proterozoic, at the same time that evidence for complex multicellularity and locomotion in animals appears in siliciclastic "Ediacaran" rocks in the form of body and trace fossils.

NASA Program Exobiology↗
NASA NTRS1993

Insect diversity in the fossil record

Insects possess a surprisingly extensive fossil record. Compilation of the geochronologic ranges of insect families demonstrates that their diversity exceeds that of preserved vertebrate tetrapods through 91 percent of their evolutionary history. The great diversity of insects was achieved not by high origination rates but rather by low extinction rates comparable to the low rates of slowly evolving marine invertebrate groups. The great radiation of modern insects began 245 million years ago and was not accelerated by the expansion of angiosperms during the Cretaceous period. The basic trophic machinery of insects was in place nearly 100 million years before angiosperms appeared in the fossil record.

NASA Discipline Exobiology↗
NASA NTRS2020

Increasing anthropogenic methane emissions arise equally from agricultural and fossil fuel sources

Climate stabilization remains elusive, with increased greenhouse gas concentrations already increasing global average surface temperatures 1.1°C above pre-industrial levels (World Meteorological Organization 2019). Carbon dioxide (CO2) emissions from fossil fuel use, deforestation, and other anthropogenic sources reached ~ 43 billion metric tonnes in 2019 (Friedlingstein et al 2019, Jackson et al 2019). Storms, floods, and other extreme weather events displaced a record 7 million people in the first half of 2019 (IDMC 2019). When global mean surface temperature four million years ago was 2°C–3°C warmer than today (a likely temperature increase before the end of the century), ice sheets in Greenland and West Antarctica melted and parts of East Antarctica’s ice retreated, causing sea levels to rise 10–20 m (World Meteorological Organization 2019). Methane (CH4) emissions have contributed almost one quarter of the cumulative radiative forcings for CO2, CH4, and N2O (nitrous oxide) combined since 1750 (Etminan et al 2016). Although methane is far less abundant in the atmosphere than CO2, it absorbs thermal infrared radiation much more efficiently and, in consequence, has a global warming potential (GWP) ~86 times stronger per unit mass than CO2 on a 20-year timescale and 28- times more powerful on a 100-year time scale (IPCC 2014). Global average methane concentrations in the atmosphere reached ~1875 parts per billion (ppb) at the end of 2019, more than two-and-a-half times preindustrial levels (Dlugokencky 2020). The largest methane sources include anthropogenic emissions from agriculture, waste, and the extraction and use of fossil fuels as well as natural emissions from wetlands, freshwater systems, and geological sources (Kirschke et al 2013, Saunois et al 2016a, Ganesan et al 2019). Here, we summarize new estimates of the global methane budget based on the analysis of Saunois et al (2020) for the year 2017, the last year of the new Global Methane Budget and the most recent year data are fully available. We compare these estimates to mean values for the reference ‘stabilization’ period of 2000–2006 when atmospheric CH4 concentrations were relatively stable. We present data for sources and sinks and provide insights for the geographical regions and economic sectors where emissions have changed the most over recent decades.

fossil fuel sources↗
NASA NTRS1974

Comparative evaluation of solar, fission, fusion, and fossil energy resources. Part 5: Conclusions and recomendations

Air pollution resulting from the use of fossil fuels is discussed. Phenomena relating to the emission of CO2 such as the greenhouse effect and multiplier effect are explored. Particulate release is also discussed. The following recommendations are made for the elimination of fossil fuel combustion products in the United States: development of nuclear breeder reactors, use of solar energy systems, exploration of energy alternatives such as geothermal and fusion, and the substitution of coal for gas and oil use.

Williams, J. R.↗
NASA NTRS1987

Microbial trace-fossil formation, biogenous, and abiotic weathering in the Antarctic cold desert

In the Antarctic cold desert (Ross Desert), the survival of the cryptoendolithic microorganisms that colonize the near-surface layer of porous sandstone rocks depends on a precarious equilibrium of biological and geological factors. An unfavorable shift of this equilibrium results in death, and this may be followed by formation of trace fossils that preserve the characteristic iron-leaching pattern caused by microbial activity. Similar microbial trace fossils may exist in the geological record. If life ever arose on early Mars, similar processes may have occurred there and left recognizable traces.

Friedmann, E. Imre↗
NASA NTRS1988

Search for Martian fossil communities: Science strategies, sediment sites, and sample handling

The strategy for locating and sampling possible fossilized Martian organisms benefits from our experience with fossil microbial ecosystems on Earth. Evidence of early life is typically preserved as stromatolites in carbonates and cherts, and as microfossils in cherts, carbonates and shales. Stromatolites, which are laminated flat or domal structures built by microbial communities, are very likely the oldest and most widespread relics of early life. These communities flourished in supratidal to subtidal coastal benthic environments, wherever sunlight was available and where incoming sediments were insufficient to bury the communities before they became established. A logical site for such communities on Mars might be those areas in an ancient lake bed which were furthest from sediment input, but were still sufficiently shallow to have received sunlight. Therefore, although some sites within Valles Marineris might have contained ponded water, the possibly abundant sediment inputs might have overwhelmed stromatolite-like communities. Localized depressions which acted as catchment basins for ancient branched valley systems might be superior sites. Perhaps such depressions received drainage which, because of the relatively modest water discharges implied for these streams, was relatively low in transported sediment. Multiple streams converging on a single basin might have been able to maintain a shallow water environment for extended periods of time.

Desmarais, David J.↗
NASA NTRS1993

Topology of magnetic flux ropes and formation of fossil flux transfer events and boundary layer plasmas

A mechanism for the formation of fossil flux transfer events and the low-level boundary layer within the framework of multiple X-line reconnection is proposed. Attention is given to conditions for which the bulk of magnetic flux in a flux rope of finite extent has a simple magnetic topology, where the four possible connections of magnetic field lines are: IMF to MSP, MSP to IMF, IMF to IMF, and MSP to MSP. For a sufficient relative shift of the X lines, magnetic flux may enter a flux rope from the magnetosphere and exit into the magnetosphere. This process leads to the formation of magnetic flux ropes which contain a considerable amount of magnetosheath plasma on closed magnetospheric field lines. This process is discussed as a possible explanation for the formation of fossil flux transfer events in the magnetosphere and the formation of the low-latitude boundary layer.

Lee, L. C.↗
NASA NTRS1997

Microbial Fossils from Terrestrial Subsurface Hydrothermal Environments: Examples and Implications for Mars

The recognition of biological signatures in ancient epithermal deposits has special relevance for studies of early blaspheme evolution and in exploring for past life on Mars. Recently, proposals for the existence of an extensive subsurface blaspheme on Earth, dominated by chemoautotrophic microbial life, has gained prominence. However, reports of fossilized microbial remains, or biosedimentary structures (e.g. stromatolites) from the deposits of ancient subsurface systems, are rare. Microbial preservation is favoured where high population densities co-exist with rapid mineral precipitation. Near-surface epithetical systems with strong gradients in temperature and redox are good candidates for the abundant growth and fossilization of microorganisms, and are also favorable environments for the precipitation of ore minerals. Therefore, we might expect microbial remain, to be particularly well preserved in various kinds of hydrothermal and diagenetic mineral precipitates that formed below the upper temperature limit for life (approx. 120 C).

Hofmann, Beda A.↗
NASA NTRS2003

Microbial Fossils Detected in Desert Varnish

Mars Global Surveyor Thermal Emission Spectrometer data indicate regions with significant levels of hematite (_Fe2O3). Fe-oxides, like hematite, can form as aqueous mineral precipitates and as such may preserve microscopic fossils or other biosignatures. Several potential terrestrial analogues to martian hematite like hydrothermal vents have preserved microfossils. Microbial fossilization in Fe-oxides is often a function of biomineralization. For example, goethite (FeO2H) encrustation of fungal mycelia from the mid-Tertiary preserved fungal morphologies such that their genera could be determined.

Flood, B. E.↗