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The notion that RNA must have had a unique and decisive role in the development of life needs hardly be questioned. However,
the chemical complexity and other properties of RNA, such as high solubility in water and vulnerability to degradation, make
it improbable that RNA could have had an early presence in the development of life on Earth or on any comparable telluric
planet. Rather, the task of origin of life research must surely be to identify those chemical processes which could have taken
place on Earth that could accumulate the complexity and rich molecular information content needed to sustain primitive life,
and ultimately give rise to RNA. A collection of likely chemical precursors to modern biomolecules is listed here together
with calculations of their molecular complexity. These complexity scores are then used to propose an ordering, on a timescale,
of when they might have appeared on Earth. These pre-RNA living systems would have flourished during the first ~0.3 Gyrs after
the start of the Archaean era (~4.2 Gyr ago). If there ever was an “RNA-world” it could have started after that initial period
(~3.9 Gyrs ago), later to be complemented with the appearance of duplex DNA at about ~3.6 Gyrs ago, some time before the earliest
known stromatolites (~3.4 Gyr). 相似文献
3.
All known cosmic and geological conditions and laws of chemistry and thermodynamics allow that complex organic matter could
have formed spontaneously on pristine planet Earth about 4,000 mya. Simple gasses and minerals on the surface and in oceans
of the early Earth reacted and were eventually organized in supramolecular aggregates and enveloped cells that evolved into
primitive forms of life. Chemical evolution, which preceded all species of extant organisms, is a fact. In this review, we
have concentrated on experimental and theoretical research published over the last two decades, which has added a wealth of
new details and helped to close gaps in our previous understanding of this multifaceted field. Recent exciting progress in
the molecular and genetic analyses of existing life, in particular microorganisms of ancient origin, even supports the possibility
that a cellular, self-reproducing common ancestor might be assembled and resurrected in anaerobic cultures at some time in
the future. Charles Darwin did not, and indeed, could not, address and specify the earliest phases of life which preceded
the Origin of Species. However, in a famous letter, he sketched “a warm little pond with all sorts of… (chemicals, in which) …a protein was chemically
formed.” We try to trace the impact of his charming clear-sighted metaphor up to the present time. 相似文献
4.
Minerals on earth whose crystalline order has been reduced by radioactive decay of contained atoms are termed “metamict.”
They are rare and few because in most crystalline solids, atoms and vacancies are relatively mobile at terrestrial temperatures,
and radiation damage tends to be self-annealing. This is not the case in the extreme cold of deep space. Below roughly 100 K,
reduced vacancy mobility allows cosmic ray and solar wind induced lattice defects to endure and accumulate for eons, reaching
energy densities of up to MJ kg−1 in some materials. We examine the possible effects of the release of energy stored in cold deep-space materials when solid-state
defects recombine upon warming due to impacts, gravitational infall, or perihelion. Dimensional analysis suggests energetic
defect recombination in radiation-damaged “xenomict” solids in comets, and planetesimals may, in some circumstances, raise
internal temperatures enough to melt ice and volatilize frozen gases. We speculate that this may account for some cometary
outbursts and Deep Impact experiment results. Calorimetric experiments on appropriately irradiated natural and synthetic materials
are needed to further quantify these mechanisms. 相似文献
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Origin of 3He in the Earth is a mystery. Lacking a production mechanism, scientists assume 3He was trapped in the Earth, when the Earth was formed. In contrast to this assumption, we have found 3He and 3H concentrations in excess of the atmospheric values in the deep waters of the volcanic Lakes Pavin (France), Laacher (Germany)
and Nemrut (Turkey). This paper reports the result of finding 3H in these three volcanic lakes that appear to originate from the mantle. Because 3H has a half-life of 12.3 years, this 3H and the resulting 3He must have formed recently in the mantle and not be part of a primordial reservoir. The nuclear reactions that generate
tritium might be a source of “missing” energy in the interior of the Earth. 相似文献
7.
The World Year of Physics (2005) is an international celebration to commemorate the 100th anniversary of Einstein’s “Annus
Mirabilis.” The United Nations has officially declared 2005 as the International Year of Physics. However, the impact of Einstein’s
ideas was not restricted to physics. Among numerous other disciplines, Einstein also made significant and specific contributions
to Earth Sciences. His geosciences-related letters, comments, and scientific articles are dispersed, not easily accessible,
and are poorly known. The present review attempts to integrate them as a tribute to Einstein in commemoration of this centenary.
These contributions can be classified into three basic areas: geodynamics, geological (planetary) catastrophism, and fluvial
geomorphology. Regarding geodynamics, Einstein essentially supported Hapgood’s very controversial theory called Earth Crust
Displacement. With respect to geological (planetary) catastrophism, it is shown how the ideas of Einstein about Velikovsky’s
proposals evolved from 1946 to 1955. Finally, in relation to fluvial geodynamics, the review incorporates the elegant work
in which Einstein explains the formation of meandering rivers. A general analysis of his contributions is also carried out
from today’s perspective. Given the interdisciplinarity and implications of Einstein’s achievements to multiple fields of
knowledge, we propose that the year 2005 serve, rather than to confine his universal figure within a specific scientific area,
to broaden it for a better appreciation of this brilliant scientist in all of his dimensions. 相似文献
8.
Flowers adapted for hummingbird pollination are typically red. This correlation is usually explained by the assertion that
nectar- or pollen-stealing bees are “blind” to red flowers. However, laboratory studies have shown that bees are capable of
locating artificial red flowers and often show no innate preference for blue over red. We hypothesised that these findings
might be artefacts of the simplified laboratory environment. Using bumblebees (Bombus impatiens) that had been trained to visit red and blue artificial flowers, we tested whether colour preference was influenced by complexity
of the background on which they were foraging. Many bees were indifferent to flower colour when tested using a uniform green
background like those commonly used in laboratory studies, but all bees showed strong colour preferences (usually for blue)
when flowers were presented against a photograph of real foliage. Overall, preference for blue flowers was significantly greater
on the more realistic, complex background. These results support the notion that the red of “hummingbird syndrome” flowers
can function to reduce bee visits despite the ability of bees to detect red and highlight the need to consider context when
drawing inferences about pollinator preferences from laboratory data.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
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Several stages, from eggs to adults, of the water strider, Aquarius paludum (Fabricius), inhabiting fresh water are sometimes conveyed by heavy flow in the rainy or typhoon seasons in Japan to lotic
brackish water in the mouth of rivers. The water striders might then respond to salinity either by remaining to wait for extensive
rainfall to reduce osmotic pressure locally before reproducing (“breed here and later tactic”) or by flying away to reproduce
in fresh waters elsewhere (“breed elsewhere and later tactic”). All first instars died before the first molt when they were
exposed to 1.75 and 3.5% NaCl solutions in a laboratory experiment. Living on 0.5 and 0.9% solutions through larval and adult
stages slowed down larval growth and suppressed female reproduction. When exposed to the 0.5 and 0.9% solutions, 90 and 92%
of males, respectively, showed histolysis of their flight muscles. Therefore, in brackish natural habitats, larvae and adults
seem to follow the strategy “breed here and later.” When water striders were exposed to 0.9% solution either just after emergence
or 20 days later, females showed a higher flight propensity than those kept on fresh waters throughout, and they delayed the
deposition of eggs. Therefore, when conveyed to brackish water after emergence by stream flow after heavy rain, adults seem
to leave the area by flight, demonstrating the strategy “breed elsewhere and later” tactic. We conclude that water striders
use alternative tactics for responding to salinity, depending on the stage of exposure. 相似文献
11.
Kohko Tokushige Keigo Akimoto Toshimasa Tomoda 《Mitigation and Adaptation Strategies for Global Change》2007,12(7):1237-1251
CO2 geological storage will be one of the cost-effective options for global warming mitigation, and this technology is under
development widely in the world. However, the technology may face the challenge of public acceptance before its implementation.
In order to evaluate the public acceptance, questionnaire surveys were conducted among Japanese university students. A cognitive
map of geological storage, together with other major global warming mitigation options, everyday life activities, etc., was
constructed by means of a statistical analysis of the responses to the questionnaire. The risk-benefit cognitive map consists
of the following factors: “risk perception,” “benefit perception,” and “public acceptance.” The risk perception is further
disaggregated into “dread risk” and “unknown risk.” Additionally, a second survey was conducted after providing the students
with additional information on global warming and CO2 geological storage, and the effects of the information on their perceptions were evaluated. The effects of risk and benefit
perceptions on public acceptance were evaluated and discussed based on the cognitive maps representing the perceptions before
and after providing the information. The analyses revealed that the benefit perception was more influential than the risk
perception on the public acceptance of CO2 geological storage. The benefit perception increased greatly after providing the information; however, the unknown risk remained
considerably large. Further, RD&D relating unknown risk, for example, the monitoring technology for stored CO2 and the risk assessment of CO2 leakage, and the supply of related information to the public would be beneficial for increasing the public acceptance. 相似文献
12.
Schröder HC Brandt D Schlossmacher U Wang X Tahir MN Tremel W Belikov SI Müller WE 《Die Naturwissenschaften》2007,94(5):339-359
Biomineralization, biosilicification in particular (i.e. the formation of biogenic silica, SiO2), has become an exciting source of inspiration for the development of novel bionic approaches following “nature as model”.
Siliceous sponges are unique among silica forming organisms in their ability to catalyze silica formation using a specific
enzyme termed silicatein. In this study, we review the present state of knowledge on silicatein-mediated “biosilica” formation
in marine sponges, the involvement of further molecules in silica metabolism and their potential application in nanobiotechnology
and medicine.
Werner E. G. Müller dedicated this study to Prof. Vera Gamulin (Rudjer Boskovic Institute, Zagreb, Croatia) in honour of her
unique contributions in molecular evolution. 相似文献
13.
Global change, i.e. the mega-process radically transforming the relationship between nature and human civilization since
the end of World War II, is investigated from the point of view of systems analysis. It is argued that this unbridled process
should rather be domesticated by planetary control strategies transpiring from a new science called “geocybernetics”. The
formal aspects of geocybernetic theory are sketched and illustrated in a tutorial theatre world reflecting the overall environment
and development problematic. Within this setting a straightforward operationalization of the sweeping “sustainable development”
ideal through a set of concise paradigms can be achieved. Evidence is provided that geocybernetics is actually feasible on
the basis of earth system modelling and fuzzy-control techniques. 相似文献
14.
Sexually aberrant individuals, displaying both male and female characteristics, are rare in occurrence but are documented
throughout the animal kingdom. In parasitoid wasps of the genus Trichogramma, such individuals typically appear as a result of rearing Wolbachia-infected thelytokous wasps at high temperatures. Sexually aberrant Trichogramma have been referred to interchangeably in the literature as gynandromorphs, sexual mosaics and intersexes. However, accurately
used, the terms “gynandromorph” and “sexual mosaic” describe an individual composed of a mixture of genetically distinct tissues
corresponding to the sexual phenotypes observed, while “intersex” refers to an individual having a uniform genetic constitution
but with some tissues exhibiting sexual phenotypes conflicting with the associated genotype. Here, we investigate the heat-induced
production of sexually aberrant offspring by thelytokous Trichogramma kaykai. Aberrant individuals were rare, but each was characterized as one of 11 morphotypes ranging from very feminine to very masculine.
Overall, the production of aberrant individuals increased with time from the onset of maternal oviposition. However, while
the production of males also increased with time, the degree of masculinity of aberrant individuals did not; the different
morphotypes appeared to be produced haphazardly. We conclude that the aberrant individuals produced by T. kaykai are actually intersexes and not gynandromorphs. The wasp's close association with Wolbachia and the absence of intersexes in uninfected populations allow us to discuss a possible origin of the condition. 相似文献
15.
Wolfgang Wiltschko Lars Dehe Katrin Stapput Peter Thalau Roswitha Wiltschko 《Die Naturwissenschaften》2010,97(1):37-42
Under 502 nm turquoise light combined with 590 nm yellow light and in total darkness, European robins, Erithacus rubecula, no longer prefer their migratory direction, but exhibit so-called fixed direction responses that do not show the seasonal
change between spring and autumn. We tested robins under these light conditions in the local geomagnetic field of 46 μT, a
field of twice this intensity, 92 μT, and a field of three times this intensity, 138 μT. Under all three magnetic conditions,
the birds preferred the same easterly direction under turquoise-and-yellow light and the same northwesterly direction under
dark, while they were oriented in their seasonally appropriate direction under control conditions. “Fixed direction” responses
are thus not limited to a narrow intensity window as has been found for normal compass orientation. This can be attributed
to their origin in the magnetite-based receptor in the upper beak, which operates according to fundamentally different principles
than the radical pair mechanism in the retina mediating compass orientation. “Fixed direction” responses are possibly a relict
of a receptor mechanism that changed its function, now mainly providing information on magnetic intensity. 相似文献
16.
The leafhopper Scaphoideus titanus is the vector of a major phytoplasma grapevine disease, Flavescence dorée. The vector’s distribution is in Eastern and Northern
Europe, and its population dynamics varies as a function of vineyard latitude. We tested the hypothesis that hatching dynamics
are cued by cold temperatures observed in winter. We exposed eggs from a natural population to simulated “cold” and “mild”
winters and varied the exposure time at 5 °C from 0 to 63 days. We show that temperature cooling mainly affected the onset
of hatching and is negatively correlated to the cold time exposure. The majority of hatchings occurred more quickly in cold
rather than in mild winter simulated conditions, but there was no significant difference between the duration of hatching
of eggs whatever the cold time exposure. In agreement with the Northern American origin of the vector, the diapause termination
and thus the timing regulation of egg hatching require cold winters. 相似文献
17.
M. Shilo 《Die Naturwissenschaften》1980,67(8):384-389
Aquatic ecosystems include the two extremes: constant environmental conditions in the main bodies of water, and unstable fluctuating conditions in the shallow margins of the aquatic ecosystems. Aquatic microorganisms living in the main oceans can thus be characterized by a single prototype being moderately halophilic, psychrophilic, to some extreme barophilic and all must be oligotrophs managing to survive and multiply in extremely low nutrient concentrations. On the other hand those populating the shallow margins must be adapted to rapidly fluctuating environments and thus have multipotential metabolic patterns. Oscillatoria limnetica can serve as a model for this being capable of shifts from oxygenic to non-oxygenic photosynthesis, having multiple dark energy generating systems, fixing nitrogen anaerobically and capable of induction of resistance mechanisms to overcome oxygen toxicity. 相似文献
18.
Georg Steinhauser Johannes H. Sterba Eliezer Oren Michaela Foster Max Bichler 《Die Naturwissenschaften》2010,97(4):403-410
Seven pumice samples from excavations in North Sinai have been investigated with respect to their geochemical composition.
This type of volcanic rock has been used as an abrasive and thus has been an object of trade since antiquity. With the help
of Instrumental Neutron Activation Analysis, six of these Bronze Age samples could be correlated to their volcanic sources
on the islands of Santorini, Nisyros and Giali (Greece) using the typical element concentrations (“chemical fingerprint”).
The source of one pumice sample remains unidentified excluding, however, the Santorini eruption as a possible source. The
concluding section of this article discusses the possible contribution, however indirect, of the pumice from Sinai and elsewhere
in the Eastern Mediterranean to the controversial issue of the accurate date of the “Minoan” eruption of Santorini. 相似文献
19.
Social wasps from temperate zones have clear annual colony cycles, and the young queens hibernate during winter. In the subtropics, the only previously reported evidence for the existence of “hibernation” is the facultative winter aggregations of females during harsh climate conditions. As in temperate-zone species analyzed so far, we show in this study that in the paper wasp, Polistes versicolor, a subtropical species, body size increases as an unfavorable season approaches. Our morphological studies indicate that larger females come from winter aggregations—that is, they are new queens. Multivariate analyses indicate that size is the only variable analyzed that shows a relationship to the differences. Given the absence of a harsh climate, we suggest that the occurrence of winter aggregations in tropical P. versicolor functions to allow some females to wait for better environmental conditions to start a new nest, rather than all being obliged to start a new nest as soon as they emerge. 相似文献
20.
Social harmony often relies on ritualised dominance interactions between society members, particularly in queenless ant societies,
where colony members do not have developmentally predetermined castes but have to fight for their status in the reproductive
and work hierarchy. In this behavioural plasticity, their social organisation resembles more that of vertebrates than that
of the “classic” social insects. The present study investigates the neurochemistry of the queenless ant species, Streblognathus peetersi, to better understand the neural basis of the high behavioural plasticity observed in queenless ants. We report measurements
of brain biogenic amines [octopamine, dopamine, serotonin] of S. peetersi ants; they reveal a new set of biogenic amine influences on social organisation with no common features with other “primitively
organised societies” (bumble bees) and some common features with “highly eusocial” species (honey bees). This similarity to
honey bees may either confirm the heritage of queenless species from their probably highly eusocial ancestors or highlight
independent patterns of biogenic amine influences on the social organisation of these highly derived species. 相似文献