Mars: was There an Ancient Eden?

1997 ◽  
Vol 161 ◽  
pp. 203-218 ◽  
Author(s):  
Tobias C. Owen
Keyword(s):  
Positive Answer ◽  
Biogenic Elements ◽  
Habitable Zones ◽  
The Face ◽  
The Origin Of Life ◽  
Early Mars ◽  
Favorable Conditions ◽  
Open Question ◽  
Rocky Planets ◽  
Impact Erosion

AbstractThe clear evidence of water erosion on the surface of Mars suggests an early climate much more clement than the present one. Using a model for the origin of inner planet atmospheres by icy planetesimal impact, it is possible to reconstruct the original volatile inventory on Mars, starting from the thin atmosphere we observe today. Evidence for cometary impact can be found in the present abundances and isotope ratios of gases in the atmosphere and in SNC meteorites. If we invoke impact erosion to account for the present excess of129Xe, we predict an early inventory equivalent to at least 7.5 bars of CO2. This reservoir of volatiles is adequate to produce a substantial greenhouse effect, provided there is some small addition of SO2(volcanoes) or reduced gases (cometary impact). Thus it seems likely that conditions on early Mars were suitable for the origin of life – biogenic elements and liquid water were present at favorable conditions of pressure and temperature. Whether life began on Mars remains an open question, receiving hints of a positive answer from recent work on one of the Martian meteorites. The implications for habitable zones around other stars include the need to have rocky planets with sufficient mass to preserve atmospheres in the face of intensive early bombardment.

The Evolutionary Diversity and Ecological Complexity of Coral Reefs

2011 ◽  
Vol 17 ◽  
pp. 111-120 ◽  
Author(s):  
Nancy Knowlton ◽  
Jeremy Jackson
Keyword(s):  
Coral Reefs ◽  
Small Proportion ◽  
Fossil Record ◽  
Marine Species ◽  
Foreseeable Future ◽  
Ecological Complexity ◽  
The Face ◽  
Open Question ◽  
Trophic Linkages ◽  
Bounce Back

Coral reefs are the most biodiverse marine ecosystems on the planet, with at least one quarter of all marine species associated with reefs today. This diversity, which remains very poorly understood, is nevertheless extraordinary when one considers the small proportion of ocean area that is occupied by coral reefs. Networks of competitive and trophic linkages are also exceptionally complex and dense. Reefs have a long fossil record, although extensive reef building comes and goes. In the present, coral reefs sometimes respond dramatically to disturbances, and collapses are not always followed by recoveries. Today, much of this failure to recover appears to stem from the fact that most reefs are chronically stressed by human activities, judging by observations of recovery at exceptional locations where local human activity is minimal. How long reefs can continue to bounce back in the face of warming and acidification remains an open question. Another big uncertainty is how much loss of biodiversity will occur with the inevitable degradation of coral reefs that will continue in most places for the foreseeable future.

Hardy spaces on ZN

2002 ◽  
Vol 132 (1) ◽  
pp. 25-43 ◽  
Author(s):  
Santiago Boza ◽  
María J. Carro
Keyword(s):  
Maximal Function ◽  
Hardy Spaces ◽  
Atomic Decomposition ◽  
Classical Case ◽  
Positive Answer ◽  
Riesz Transforms ◽  
Homogeneous Type ◽  
Spaces Of Homogeneous Type ◽  
Definition Of ◽  
Open Question

The work of Coifman and Weiss concerning Hardy spaces on spaces of homogeneous type gives, as a particular case, a definition of Hp(ZN) in terms of an atomic decomposition.Other characterizations of these spaces have been studied by other authors, but it was an open question to see if they can be defined, as it happens in the classical case, in terms of a maximal function or via the discrete Riesz transforms.In this paper, we give a positive answer to this question.

scholarly journals Phenotypic states become increasingly sensitive to perturbations near a bifurcation in a synthetic gene network

eLife ◽  
2015 ◽  
Vol 4 ◽  
Author(s):  
Kevin Axelrod ◽  
Alvaro Sanchez ◽  
Jeff Gore
Keyword(s):  
Gene Network ◽  
Environmental Variability ◽  
Synthetic Gene ◽  
Phenotypic Switching ◽  
Proper Function ◽  
Critical Transition ◽  
Environmental Perturbations ◽  
The Face ◽  
Synthetic Gene Network ◽  
Open Question

Microorganisms often exhibit a history-dependent phenotypic response after exposure to a stimulus which can be imperative for proper function. However, cells frequently experience unexpected environmental perturbations that might induce phenotypic switching. How cells maintain phenotypic states in the face of environmental fluctuations remains an open question. Here, we use environmental perturbations to characterize the resilience of phenotypic states in a synthetic gene network near a critical transition. We find that far from the critical transition an environmental perturbation may induce little to no phenotypic switching, whereas close to the critical transition the same perturbation can cause many cells to switch phenotypic states. This loss of resilience was observed for perturbations that interact directly with the gene circuit as well as for a variety of generic perturbations-such as salt, ethanol, or temperature shocks-that alter the state of the cell more broadly. We obtain qualitatively similar findings in natural gene circuits, such as the yeast GAL network. Our findings illustrate how phenotypic memory can become destabilized by environmental variability near a critical transition.

Autocatalytic chemical networks preceded proteins and RNA in evolution

2019 ◽  
Author(s):  
Joana C. Xavier ◽  
Wim Hordijk ◽  
Stuart Kauffman ◽  
Mike Steel ◽  
William F. Martin
Keyword(s):  
Amino Acids ◽  
Origin Of Life ◽  
Small Molecule ◽  
Metabolic Networks ◽  
Early Earth ◽  
Prebiotic Evolution ◽  
Biochemical Evolution ◽  
The Origin Of Life ◽  
Acids And Bases ◽  
Open Question

AbstractModern cells embody metabolic networks containing thousands of elements and form autocatalytic molecule sets that produce copies of themselves. How the first self-sustaining metabolic networks arose at life’ s origin is a major open question. Autocatalytic molecule sets smaller than metabolic networks were proposed as transitory intermediates at the origin of life, but evidence for their role in prebiotic evolution is lacking. Here we identify reflexively autocatalytic food-generated networks (RAFs)—self-sustaining networks that collectively catalyze all their reactions—embedded within microbial metabolism. RAFs in the metabolism of ancient anaerobic autotrophs that live from H2 and CO2 generate amino acids and bases, the monomeric components of protein and RNA, and acetyl-CoA, but amino acids and bases do not generate metabolic RAFs, indicating that small-molecule catalysis preceded polymers in biochemical evolution. RAFs uncover intermediate stages in the origin of metabolic networks, narrowing the gaps between early-Earth chemistry and life.

scholarly journals Water delivery by pebble accretion to rocky planets in habitable zones in evolving disks

2019 ◽  
Vol 624 ◽  
pp. A28 ◽  
Author(s):  
Shigeru Ida ◽  
Takeru Yamamura ◽  
Satoshi Okuzumi
Keyword(s):  
Analytical Formula ◽  
Outer Edge ◽  
Water Delivery ◽  
Water Fraction ◽  
The Earth ◽  
Exoplanetary Systems ◽  
Habitable Zones ◽  
Disk Size ◽  
1D Model ◽  
Rocky Planets

Context. The ocean mass of the Earth is only 2.3 × 10−4 of the whole planet mass. Even including water in the interior, the water fraction would be at most 10−3−10−2. Ancient Mars may have had a similar or slightly smaller water fraction. What controlled the amount of water in these planets has not been clear, although several models have been proposed. It is important to clarify the control mechanism to discuss water delivery to rocky planets in habitable zones in exoplanetary systems, as well as that to Earth and Mars in our solar system. Aims. We consider water delivery to planets by icy pebbles after the snowline inwardly passes planetary orbits. We derive the water mass fraction (fwater) of the final planet as a function of disk parameters and discuss the parameters that reproduce a small value of fwater comparable to that inferred for the Earth and ancient Mars. Methods. We calculated the growth of icy dust grains to pebbles and the pebble radial drift with a 1D model, by simultaneously solving the snowline migration and dissipation of a gas disk. With the obtained pebble mass flux, we calculated accretion of icy pebbles onto planets after the snowline passage to evaluate fwater of the planets. Results. We find that fwater is regulated by the total mass (Mres) of icy dust materials preserved in the outer disk regions at the timing (t = tsnow) of the snowline passage of the planetary orbit. Because Mres decays rapidly after the pebble formation front reaches the disk outer edge (at t = tpff), fwater is sensitive to the ratio tsnow∕tpff, which is determined by the disk parameters. We find tsnow∕tpff < 10 or > 10 is important. By evaluating Mres analytically, we derive an analytical formula of fwater that reproduces the numerical results. Conclusions. Using the analytical formula, we find that fwater of a rocky planet near 1 au is similar to the Earth, i.e., ~10−4−10−2, in disks with an initial disk size of 30–50 au and an initial disk mass accretion rate of ~(10−8−10−7) M⊙ yr−1 for disk depletion timescale of approximately a few M yr. Because these disks may be median or slightly compact/massive disks, our results suggest that the water fraction of rocky planets in habitable zones may often be similar to that of the Earth if icy pebble accretion is responsible for water delivery.

scholarly journals Atmospheric Parameters and Luminosities of Nearby M Dwarfs – Estimating Habitable Exoplanet Detectability with the E-ELT

2016 ◽  
Vol 12 (S328) ◽  
pp. 371-373
Author(s):  
Gustavo F. Porto de Mello ◽  
Riano E. Giribaldi ◽  
Diego Lorenzo-Oliveira ◽  
Nathália M. Paes Leme
Keyword(s):  
Spectral Line ◽  
Detailed Analysis ◽  
Atmospheric Parameters ◽  
M Dwarfs ◽  
Habitable Zones ◽  
Pca Method ◽  
Rocky Planets

AbstractWe derive Teff and [Fe/H] for a sample of 72 nearby M-dwarfs with Hipparcos parallaxes and δ < +30. Spectra, acquired at the Observatório do Pico dos Dias, Brazil, have R = 10,000 and S/N ≳ 100 for nearly all targets in the λλ8380-8880 range. Atmospheric parameters were derived from VJHK colors and a system of spectral line indices calibrated against sample stars with interferometric Teff and [Fe/H] from detailed analysis of FGK binary companions. A PCA method of calibration yields internal errors within 70 K and 0.1 dex for Teff and [Fe/H]. For 18 stars we present the first Teff or [Fe/H] derivation in the literature. We compute the star's luminosities, calculate the position of their habitable zones and estimate that, were all of they to harbour rocky planets inside their HZ, 15–20 of these would be detectable by the E-ELT Planetary Camera and Spectrograph.

scholarly journals A Missed Partnership: Russia and the US at the Pacific

2019 ◽  
Vol 12 (1) ◽  
pp. 159-184
Author(s):  
D. V. Suslov
Keyword(s):  
United States ◽  
The United States ◽  
Asia Pacific ◽  
Asia Pacific Region ◽  
The Pacific ◽  
The Us ◽  
The Face ◽  
Soviet Space ◽  
Favorable Conditions ◽  
Post Soviet Space

Both Russia and the United States consider the Asia-Pacific as the center of the world economy and politics and assume the active presence in the region crucial for their security and economic development. They did not have such sharp contradictions there as in Europe or in the post-Soviet space. Moreover, some of their interests in the Asia-Pacific Region coincide – such as preventing Chinese hegemony. In this regard, the Russian-American dialogue and cooperation in the Asia-Pacific could be an important pillar of the positive agenda of their relations and a factor in their sustainability. Due to foreign policy inertia, the inflexibility of the agenda of Russian-American relations and the inability of the parties to go beyond the usual pattern, such a dialogue has not even begun. Both sides demonstrated strategic myopia. This weakened the resilience of US-Russian relations in the face of new challenges and accelerated their deterioration and disruption to a new confrontation. The Asia-Pacific has become another theater of the US-Russian systemic confrontation. However, it is in the interest of bothRussia and the United States to separate relations in this region from their general confrontation. This will create favorable conditions for Russia to build a balanced partnership system in the Asia-Pacific, which is necessary to consolidate its role as an independent global great power. In addition, the Russian-American dialogue on the Asia-Pacific, or at least the weakening of their confrontation in this region, will reduce its polarization and prevent tensions between the US and its Asian allies and partners.

scholarly journals Civil liability for doctors in the face of a professional (medical) error

2021 ◽  
Vol 27 (1) ◽  
pp. 29-35
Author(s):  
Velisav Marković
Keyword(s):  
Medical Errors ◽  
Medical Error ◽  
Healthcare Workers ◽  
Work Organization ◽  
Civil Liability ◽  
Medical Law ◽  
Effect Relationship ◽  
The Face ◽  
Court Proceedings ◽  
Open Question

Civil liability for healthcare workers and healthcare institutions is one of the most significant problems in Health and Medical Law. The basis of responsibility is always an open question, whether it be medical errors, misinformation or faulty work organization. Aiming to make things clearer for individuals practising medicine, this paper presents the concept of a professional (medical) error, the basis of responsibility for the doctor (medical error, damage to the patient and the cause-and-effect relationship between a medical error and the damage caused) as well as the precise explanation of who has to prove what in possible court proceedings.

scholarly journals Forest Saccharomyces paradoxus are robust to seasonal biotic and abiotic changes

2020 ◽  
Author(s):  
Primrose J. Boynton ◽  
Dominika Wloch-Salamon ◽  
Doreen Landermann ◽  
Eva H. Stukenbrock
Keyword(s):  
Environmental Changes ◽  
Interference Competition ◽  
Seasonal Adaptation ◽  
Saccharomyces Paradoxus ◽  
Selective Pressures ◽  
Killer Toxins ◽  
Four Seasons ◽  
Environmental Fluctuations ◽  
The Face ◽  
Open Question

AbstractMicroorganisms are famous for adapting quickly to new environments. However, most evidence for rapid microbial adaptation comes from laboratory experiments or domesticated environments, and it is unclear how rates of adaptation scale from human-influenced environments to the great diversity of wild microorganisms. We examined potential monthly-scale selective pressures in the model forest yeast Saccharomyces paradoxus. Contrary to expectations of seasonal adaptation, the S. paradoxus population was stable over four seasons in the face of abiotic and biotic environmental changes. While the S. paradoxus population was diverse, including 41 unique genotypes among 192 sampled isolates, there was no correlation between S. paradoxus genotypes and seasonal environments. Consistent with observations from other S. paradoxus populations, the forest population was highly clonal and inbred. This lack of recombination, paired with population stability, implies that S. paradoxus evolved the phenotypic plasticity needed to resist seasonal environmental fluctuations long ago, and that individual S. paradoxus are generalists with regard to seasonal environments. Similarly, while the forest population included diversity among phenotypes related to intraspecific interference competition, there was no evidence for active coevolution among these phenotypes. At least ten percent of the forest S. paradoxus individuals produced “killer toxins”, which kill sensitive Saccharomyces cells, but the presence of a toxin-producing isolate did not predict resistance to the toxin among nearby isolates. How forest yeasts acclimate to changing environments remains an open question, and future studies should investigate the physiological responses that allow microbial cells to cope with environmental fluctuations in their native habitats.

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