scholarly journals Earth's earliest and deepest purported fossils may be iron-mineralized chemical gardens

2019 ◽  
Vol 286 (1916) ◽  
pp. 20192410 ◽  
Author(s):  
Sean McMahon
Keyword(s):  
Cross Sections ◽  
Constant Thickness ◽  
Biological Origin ◽  
Origin And Evolution ◽  
Iron Mineral ◽  
Fossil Fungi ◽  
Morphological Criteria ◽  
Life On Mars ◽  
Rock Record ◽  
Chemical Gardens

Recognizing fossil microorganisms is essential to the study of life's origin and evolution and to the ongoing search for life on Mars. Purported fossil microbes in ancient rocks include common assemblages of iron-mineral filaments and tubes. Recently, such assemblages have been interpreted to represent Earth's oldest body fossils, Earth's oldest fossil fungi, and Earth's best analogues for fossils that might form in the basaltic Martian subsurface. Many of these putative fossils exhibit hollow circular cross-sections, lifelike (non-crystallographic, constant-thickness, and bifurcate) branching, anastomosis, nestedness within ‘sheaths’, and other features interpreted as strong evidence for a biological origin, since no abiotic process consistent with the composition of the filaments has been shown to produce these specific lifelike features either in nature or in the laboratory. Here, I show experimentally that abiotic chemical gardening can mimic such purported fossils in both morphology and composition. In particular, chemical gardens meet morphological criteria previously proposed to establish biogenicity, while also producing the precursors to the iron minerals most commonly constitutive of filaments in the rock record. Chemical gardening is likely to occur in nature. Such microstructures should therefore not be assumed to represent fossil microbes without independent corroborating evidence.

scholarly journals GEOMETRIC MODELING OF A SHAPE OF PARALLELOGRAM PLATES IN A PROBLEM OF FREE VIBRATIONS USING CONFORMAL RADII

2021 ◽  
pp. 143-159
Author(s):  
A.A. Chernyaev ◽  
Keyword(s):  
Cross Sections ◽  
Geometric Modeling ◽  
Interpolation Method ◽  
Geometric Characteristic ◽  
Free Vibrations ◽  
Theory Of Elasticity ◽  
Constant Thickness ◽  
Basic Frequency ◽  
Plate Vibrations ◽  
The Subject

The paper considers a method of geometric modeling applied when solving basic twodimensional problems of the theory of elasticity and structural mechanics, in particular the applied problems of engineering. The subject of this study is vibrations of thin elastic parallelogram plates of constant thickness. To determine a basic frequency of vibrations, the interpolation method based on the geometric characteristic of the shape of plates (membrane, cross sections of a rod) is proposed. This characteristic represents a ratio of interior and exterior conformal radii of the plate. As is known from the theory of conformal mappings, conformal radii are those obtained by mapping of a plate onto the interior and exterior of a unit disk. The paper presents basic terms, tables, and formulas related to the considered geometric method with a comparative analysis of the curve diagrams obtained using various interpolation formulas. The original computer program is also developed. The main advantage of the proposed method of determining the basic frequency of plate vibrations is a graphic representation of results that allows one to accurately determine the required solution on the graph among the other solutions corresponding to the considered case of parallelogram plates. Although there are many known approximate approaches, which are used to solve the considered problems, only geometric modeling technique based on the conformal radii ratio gives such an opportunity.

scholarly journals Fundamental molecules of life are pigments which arose and evolved to dissipate the solar spectrum

2015 ◽  
Vol 12 (3) ◽  
pp. 2101-2160 ◽  
Author(s):  
K. Michaelian ◽  
A. Simeonov
Keyword(s):  
Cross Sections ◽  
Dissipation Rate ◽  
Solar Spectrum ◽  
Photochemical Process ◽  
Physical Size ◽  
Origin And Evolution ◽  
Organic Pigments ◽  
Early Atmosphere ◽  
Evolution Of Life ◽  
History Of

Abstract. The driving force behind the origin and evolution of life has been the thermodynamic imperative of increasing the entropy production of the biosphere through increasing the global solar photon dissipation rate. In the upper atmosphere of today, oxygen and ozone derived from life processes are performing the short wavelength UVC and UVB dissipation. On Earth's surface, water and organic pigments in water facilitate the near UV and visible photon dissipation. The first organic pigments probably formed, absorbed, and dissipated at those photochemically active wavelengths in the UVC that could have reached Earth's surface during the Archean. Proliferation of these pigments can be understood as an autocatalytic photochemical process obeying non-equilibrium thermodynamic directives related to increasing solar photon dissipation rate. Under these directives, organic pigments would have evolved over time to increase the global photon dissipation rate by; (1) increasing the ratio of their effective photon cross sections to their physical size, (2) decreasing their electronic excited state life times, (3) quenching radiative de-excitation channels (e.g. fluorescence), (4) covering ever more completely the prevailing solar spectrum, and (5) proliferating and dispersing to cover an ever greater surface area of Earth. From knowledge of the evolution of the spectrum of G-type stars, and considering the most probable history of the transparency of Earth's atmosphere, we construct the most probable Earth surface solar spectrum as a function of time and compare this with the history of molecular absorption maxima obtained from the available data in the literature. This comparison supports the conjecture that many fundamental molecules of life are pigments which arose and evolved to dissipate the solar spectrum, supports the thermodynamic dissipation theory for the origin of life, constrains models for Earth's early atmosphere, and sheds some new light on the origin of photosynthesis.

scholarly journals Catalytic/Protective Properties of Martian Minerals and Implications for Possible Origin of Life on Mars

Life ◽  
2018 ◽  
Vol 8 (4) ◽  
pp. 56 ◽  
Author(s):  
Teresa Fornaro ◽  
Andrew Steele ◽  
John Brucato
Keyword(s):  
Organic Compounds ◽  
Building Blocks ◽  
Life Forms ◽  
Degradation Mechanisms ◽  
Protective Properties ◽  
Origin And Evolution ◽  
Life On Mars ◽  
Insight Into ◽  
Shed Light

Minerals might have played critical roles for the origin and evolution of possible life forms on Mars. The study of the interactions between the “building blocks of life” and minerals relevant to Mars mineralogy under conditions mimicking the harsh Martian environment may provide key insight into possible prebiotic processes. Therefore, this contribution aims at reviewing the most important investigations carried out so far about the catalytic/protective properties of Martian minerals toward molecular biosignatures under Martian-like conditions. Overall, it turns out that the fate of molecular biosignatures on Mars depends on a delicate balance between multiple preservation and degradation mechanisms, often regulated by minerals, which may take place simultaneously. Such a complexity requires more efforts in simulating realistically the Martian environment in order to better inspect plausible prebiotic pathways and shed light on the nature of the organic compounds detected both in meteorites and on the surface of Mars through in situ analysis.

scholarly journals Fundamental molecules of life are pigments which arose and co-evolved as a response to the thermodynamic imperative of dissipating the prevailing solar spectrum

2015 ◽  
Vol 12 (16) ◽  
pp. 4913-4937 ◽  
Author(s):  
K. Michaelian ◽  
A. Simeonov
Keyword(s):  
Cross Sections ◽  
Dissipation Rate ◽  
Solar Spectrum ◽  
Photochemical Process ◽  
Origin And Evolution ◽  
Organic Pigments ◽  
Early Atmosphere ◽  
Evolution Of Life ◽  
History Of ◽  
Uv C

Abstract. The driving force behind the origin and evolution of life has been the thermodynamic imperative of increasing the entropy production of the biosphere through increasing the global solar photon dissipation rate. In the upper atmosphere of today, oxygen and ozone derived from life processes are performing the short-wavelength UV-C and UV-B dissipation. On Earth's surface, water and organic pigments in water facilitate the near-UV and visible photon dissipation. The first organic pigments probably formed, absorbed, and dissipated at those photochemically active wavelengths in the UV-C and UV-B that could have reached Earth's surface during the Archean. Proliferation of these pigments can be understood as an autocatalytic photochemical process obeying non-equilibrium thermodynamic directives related to increasing solar photon dissipation rate. Under these directives, organic pigments would have evolved over time to increase the global photon dissipation rate by (1) increasing the ratio of their effective photon cross sections to their physical size, (2) decreasing their electronic excited state lifetimes, (3) quenching radiative de-excitation channels (e.g., fluorescence), (4) covering ever more completely the prevailing solar spectrum, and (5) proliferating and dispersing to cover an ever greater surface area of Earth. From knowledge of the evolution of the spectrum of G-type stars, and considering the most probable history of the transparency of Earth's atmosphere, we construct the most probable Earth surface solar spectrum as a function of time and compare this with the history of molecular absorption maxima obtained from the available data in the literature. This comparison supports the conjecture that many fundamental molecules of life are pigments which arose, proliferated, and co-evolved as a response to dissipating the solar spectrum, supports the thermodynamic dissipation theory for the origin of life, constrains models for Earth's early atmosphere, and sheds some new light on the origin of photosynthesis.

Bimodal Optimization of Compressed Columns on Elastic Foundations

1986 ◽  
Vol 53 (1) ◽  
pp. 130-134 ◽  
Author(s):  
R. H. Plaut ◽  
L. W. Johnson ◽  
N. Olhoff
Keyword(s):  
Optimal Design ◽  
Cross Sections ◽  
Variable Thickness ◽  
Buckling Load ◽  
Optimal Designs ◽  
Constant Thickness ◽  
Buckling Modes ◽  
Elastic Foundations ◽  
Bimodal Optimization ◽  
Lightweight Core

We consider columns attached to elastic foundations and compressed by axial end loads. Pinned-pinned, clamped-clamped, and pinned-clamped boundary conditions are treated. The columns have rectangular sandwich cross sections with a fixed lightweight core and identical face sheets of variable thickness. For given total volume, we optimize the variation of the thickness along the column so as to maximize the buckling load. In most cases, the optimal design is bimodal (i.e., associated with two buckling modes). The optimal designs depend on the foundation stiffness, and the largest increase in buckling load relative to a column with constant thickness is 22 percent.

Where is the nitrogen on Mars?

2003 ◽  
Vol 2 (3) ◽  
pp. 217-225 ◽  
Author(s):  
Rocco L. Mancinelli ◽  
Amos Banin
Keyword(s):  
Organic Molecules ◽  
Essential Element ◽  
Crystal Lattices ◽  
Origin And Evolution ◽  
Thermal Escape ◽  
Martian Soil ◽  
Evolution Of Life ◽  
Life On Mars ◽  
Nitrogen Abundance ◽  
Living Organisms

Nitrogen is an essential element for life. Specifically, fixed nitrogen (i.e. NH3, NH4+, NOx or N that is chemically bound to either inorganic or organic molecules and can be released by hydrolysis to form NH3 or NH4+) is useful to living organisms. Nitrogen on present-day Mars has been analysed only in the atmosphere. The inventory is a small fraction of the amount of nitrogen presumed to have been received by the planet during its accretion. Where is the missing nitrogen? Answering this question is crucial for understanding the probability of the origin and evolution of life on Mars, and for its future astrobiological exploration. The two main processes that could have removed nitrogen from the atmosphere include: (1) non-thermal escape of N atoms to space and (2) burial within the regolith as nitrates and ammonium salts. Nitrate would probably be stable in the highly oxidized surface soil of Mars and could have served as an NO3− sink. Such accumulations are observed in certain desert environments on Earth. Some NH4+ nitrogen may also be fixed and stabilized in the soil by inclusion as a structural cation in the crystal lattices of certain phyllosilicates replacing K+. Analysis of the Martian soil for traces of NO3− and NH4+ during future missions will provide important information regarding the nitrogen abundance on Mars. We hypothesize that Mars soil, as typical of extremely dry desert soils on Earth, is likely to contain at least some of the missing nitrogen as nitrate salts and some fixed ammonium bound to aluminosilicate minerals.

On the Torsion of Rectangular Sandwich Plates

1956 ◽  
Vol 23 (2) ◽  
pp. 191-194
Author(s):  
Paul Seide
Keyword(s):  
Cross Sections ◽  
Torsional Rigidity ◽  
Constant Thickness ◽  
Sandwich Plates ◽  
The Core ◽  
Equal Thickness ◽  
Rectangular Sandwich Plates

Abstract The torsional rigidity of rectangular sandwich plates of constant thickness is calculated, with cross sections assumed free to warp. The faces are isotropic and of equal thickness while the core may be orthotropic, the axes of orthotropy coinciding with co-ordinate axes of the structure.

From Chemical Gardens to Fuel Cells: Generation of Electrical Potential and Current Across Self-Assembling Iron Mineral Membranes

2015 ◽  
Vol 54 (28) ◽  
pp. 8184-8187 ◽  
Author(s):  
Laura M. Barge ◽  
Yeghegis Abedian ◽  
Michael J. Russell ◽  
Ivria J. Doloboff ◽  
Julyan H. E. Cartwright ◽  
...  
Keyword(s):  
Fuel Cells ◽  
Electrical Potential ◽  
Iron Mineral ◽  
Self Assembling ◽  
Chemical Gardens

Introduction to Radiometric Dating

2006 ◽  
Vol 12 ◽  
pp. 1-23 ◽  
Author(s):  
Brent V. Miller
Keyword(s):  
Time Scale ◽  
Radiometric Dating ◽  
Current Status ◽  
Origin And Evolution ◽  
Geologic Time ◽  
The Earth ◽  
Dating Methods ◽  
Rock Record ◽  
Geologic Time Scale ◽  
Radiometric Dates

Radiometric dating of rocks and minerals to constrain the age of the Earth, timing of geological events and paleobiological histories has its roots in the works of nuclear physicists of the early Nineteenth Century during the period of discovery of radioactivity and investigations into the nature of the atom. The intervening years since have seen great progress in using the long-lived radioactive elements to constrain the origin and evolution of the Earth and to place the rock and fossil record into a consistent, numerically quantifiable temporal framework.U-Th-Pb and40Ar/39Ar dating methods have emerged as the primary tools for calibrating most of Earth history. It is important for all geoscientists to appreciate the physical basis underlying these methods and to have the ability to evaluate dates by means of currently accepted practices of data presentation. This introduction, along with the accompanying chapters, is intended to help the consumers of radiometric dates to understand better the uses and limitations of radiometric dating methods in an effort to tailor methods and techniques to address specific geochronologic needs, including calibration of the geologic time scale.The ultimate goal of a fully calibrated rock record remains an on-going endeavor. The 2004 ICS geologic time scale is the latest compilation of those efforts. The numerical age calibration is constrained by only 213 radiometric dates, the vast majority of which are U-Pb and40Ar/39Ar dates. Radiometric age control is not evenly distributed through geologic time. There are virtually no radiometric dates in the late Cenozoic where magnetostratigraphy and cyclostratigraphic methods are more precise and applicable. Radiometric dating efforts are concentrated on biostratigraphically important segments of the rock record such as the Permian-Triassic and Cretaceous-Paleocene boundary events, and this is reflected in high-precision calibration of these boundaries. Large segments of geologic time, however, are constrained by either a few radiometric dates per chronostratigraphic unit (most of the Paleozoic) or none at all (Upper Triassic). The current status of radiometric age control on the rock record largely reflects real, underlying scientific issues in biostratigraphy and geochronology, and thus can help point the way to fruitful lines of collaboration between paleontologists, stratigraphers, and geochronologists.

On Torsion of Closed Thin-Wall Members With Arbitrary Stress-Strain Laws: A General Criterion for Cross Sections Exhibiting No Warping

2000 ◽  
Vol 67 (3) ◽  
pp. 460-464 ◽  
Author(s):  
A. Chiskis ◽  
R. Parnes
Keyword(s):  
Shear Stress ◽  
Cross Sections ◽  
Small Strain ◽  
Constant Thickness ◽  
General Criterion ◽  
Thin Wall ◽  
Stress Strain

Warping due to torsion of closed thin-wall elastic members having constant thickness is investigated under the assumption of small strain but with arbitrary isotropic shear stress-strain laws. Based on a derived general criterion, it is shown that there exists a class of cross-sections which undergo no warping. For cases where warping exists, an example of simplified calculations, using the derived expressions, is presented for warping of a thin-wall rectangle. [S0021-8936(00)03503-0]

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