Cosmic radiation and evolution of life on earth: roles of environment, adaptation and selection.

The role of ionizing radiation in general, and cosmic radiation in particular, in the evolution of organisms on the earth by adaptation and natural selection is considered in a series of questions: (1) Are there times during the evolution of the earth and of life when genetic material could be exposed to heavy ion radiation? (2) Throughout the course of chemical and biological evolution on the earth, what fraction of environmental mutagenesis could be attributable to cosmic and/or solar ionizing radiation? (3) Is ionizing radiation an agent of adaptation or selection, or both? (4) What can the cladistics of the evolution of genetic repair tell us about the global history of genotoxic selection pressures? (5) How much genetic diversity can be attributed to the selection of radiation-damage repair processes?     

Understanding plant-soil relationships using controlled environment facilities.

Although soil is a component of terrestrial ecosystems, it is comprised of a complex web of interacting organisms, and therefore can be considered itself as an ecosystem. Soil microflora and fauna derive energy from plants and plant residues and serve important functions in maintaining soil physical and chemical properties, thereby affecting net primary productivity (NPP), and in the case of contained environments, the quality of the life support system. We have been using 3 controlled-environment facilities (CEF's) that incorporate different levels of soil biological complexity and environmental control, and differ in their resemblance to natural ecosystems, to study relationships among plant physiology, soil ecology, fluxes of minerals and nutrients, and overall ecosystem function. The simplest system utilizes growth chambers and specialized root chambers with organic-less media to study the physiology of plant-mycorrhizal associations. A second system incorporates natural soil in open-top chambers to study soil bacterial and fungal population response to stress. The most complex CEF incorporates reconstructed soil profiles in a "constructed" ecosystem, enabling close examination of the soil foodweb. Our results show that closed ecosystem research is important for understanding mechanisms of response to ecosystem stresses. In addition, responses observed at one level of biological complexity may not allow prediction of response at a different level of biological complexity. In closed life support systems, incorporating soil foodwebs will require less artificial manipulation to maintain system stability and sustainability.     

Life on Mars? I. The chemical environment.

The origin of life at its abiotic evolutionary stage, requires a combination of constituents and environmental conditions that enable the synthesis of complex replicating macromolecules from simpler monomeric molecules. It is very likely that the early stages of this evolutionary process have been spontaneous, rapid and widespread on the surface of the primitive Earth, resulting in the formation of quite sophisticated living organisms within less than a billion years. To what extent did such conditions prevail on Mars? Two companion-papers (Life on Mars? I and II) will review and discuss the available information related to the chemical, physical and environmental conditions on Mars and assess it from the perspective of potential exobiological evolution.     

Self-restoration of biocomponents as a mean to enhance Biological Life Support Systems reliability.

One of the key problems of long-term space missions is limited service life of units. The only exceptions are biological components of biological Life Support Systems--higher plants or microorganisms. These components are capable of self-restoration: after complete disintegration, they can appear again from seeds or spores. The estimate of failure intensity of BLSS regeneration component includes: a number of self-sustained sections of the regeneration component; permissible boost (how many times can productivity of a component be increased); time required to repair (restore) a component; the crew existence time, when all LSS regeneration components fail; failure rate of one section of a regeneration component. Evaluations show that for hydrogen-oxidizing bacteria and micro-algae very high reliability is achieved even for one or two sections. In the case of higher plants (due to low rate of self-restoration) bio-regenerative module has to be divided into 10 self-sustained sections operating simultaneously. These measures can decrease the probability of catastrophe by a factor of 10(6).     

Exobiology revisited

The term “Exobiology” was introduced about 25 years ago, at a time when intensive discussions were under way concerning plans for the biological exploration of Mars. The search for life on Mars was to be a critical test of the concept of chemical evolution- not an end in itself. After the Viking mission, when it became apparent that prospects were dim for the discovery of extraterrestrial life within our solar system, many people concluded that this new field of endeavor would soon expire. Quite the contrary, over the past decade, the field has broadened considerably into a multidisciplinary approach to understanding the circumstances that led to the origin of life and the interplay between the evolution of this planet and its biota.     

Survival of microorganisms in space protected by meteorite material: results of the experiment 'EXOBIOLOGIE' of the PERSEUS mission.

During the early evolution of life on Earth, before the formation of a protective ozone layer in the atmosphere, high intensities of solar UV radiation of short wavelengths could reach the surface of the Earth. Today the full spectrum of solar UV radiation is only experienced in space, where other important space parameters influence survival and genetic stability additionally, like vacuum, cosmic radiation, temperature extremes, microgravity. To reach a better understanding of the processes leading to the origin, evolution and distribution of life we have performed space experiments with microorganisms. The ability of resistant life forms like bacterial spores to survive high doses of extraterrestrial solar UV alone or in combination with other space parameters, e.g. vacuum, was investigated. Extraterrestrial solar UV was found to have a thousand times higher biological effectiveness than UV radiation filtered by stratospheric ozone concentrations found today on Earth. The protective effects of anorganic substances like artificial or real meteorites were determined on the MIR station. In the experiment EXOBIOLOGIE of the French PERSEUS mission (1999) it was found that very thin layers of anorganic material did not protect spores against the deleterious effects of energy-rich UV radiation in space to the expected amount, but that layers of UV radiation inactivated spores serve as a UV-shield by themselves, so that a hypothetical interplanetary transfer of life by the transport of microorganisms inside rocks through the solar system cannot be excluded, but requires the shielding of a substantial mass of anorganic substances.     

A quarantine protocol for analysis of returned extraterrestrial samples

A quarantine protocol is presented for analysis of samples of extraterrestrial material that might be returned from space to an Earth-orbiting quarantine facility. The protocol is designed to detect biologically active agents in extraterrestrial soil. Its goal is either to certify the sample safe to return to a terrestrial containment facility where extensive biological, chemical, geological and physical investigations can be conducted, or to detect “biological effects” thus dictating second order testing. The protocol requires 46 grams of a one kilogram returned sample plus 54 grams to be reserved for second order testing should that become necessary. The protocol operates at two levels. First, it seeks to detect the presence of any replicating organisms or toxic substances using chemical analyses, microscopy, metabolic tests, and microbiological culturing techniques. The second level involves hazard evaluation by adding any agents found at the first level (or the extraterrestrial soil) to challenge cultures of terrestrial species. The specific types of experiments and the means of executing them were chosen by participants in an American Society for Engineering Education Summer Systems Design Group to provide maximum life detection sensitivity, yet are compatible with a small crew operating behind biological barriers in a condition of weightlessness.     

The closed equilibrated biological aquatic system: a 12 months test of an artificial aquatic ecosystem.

The Closed Equilibrated Biological Aquatic System" (C.E.B.A.S.) is finally disposed for long-term multi-generation experiments with aquatic organisms in a space station. Therefore a minimum operation time of three months is required. It is verified in three versions of laboratory prototypes. The third one passed successfully a 12 months mid-term test in 1995/96 thus demonstrating its high biological stability. The third version of the C.E.B.A.S. consists of a 100 l animal tank, two plant cultivators with a volume of 15 l each with independent illuminations, a 3.0 l semibiological "mechanical" filter, a 3.0 l bacteria filter, a heating/cooling device and a dummy filter unit. The live-bearing teleost Xiphophorus helleri is the vertebrate and the pulmonate water snail Biomphalana glabrata the invertebrate experimental animal in the system. The rootless higher water plant Ceratophyllum demersum is the producer organism. Ammonia oxidizing bacteria and other microorganisms settle in the filters. A sample data acquisition is combined with temperature and plant illumination control. Besides of the space aspects the C.E.B.A.S. proved to be an extremely suitable tool to investigate the organism and subcomponent interactions in a well defined terrestrial aquatic closed ecosystem by providing physical, chemical and biological data which allow an approach to a comprehensive system analysis. Moreover the C.E.B.A.S. is the base for the development of innovative combined animal-plant aquaculture systems for human nutrition on earth which could be implemented into bioregenerative life support systems with a higher degree of complexity suitable for lunar or planetary bases.     

Influence of long-term altered gravity on the swimming performance of developing cichlid fish: including results from the 2nd German Spacelab Mission D-2.

This study presents qualitative and quantitative data concerning gravity-dependent changes in the swimming behaviour of developing cichlid fish larvae (Oreochromis mossambicus) after a 9 resp. 10 days exposure to increased acceleration (centrifuge experiments), to reduced gravity (fast-rotating clinostat), changed accelerations (parabolic aircraft flights) and to near weightlessness (2nd German Spacelab Mission D-2). Changes of gravity initially cause disturbances of the swimming performance of the fish larvae. With prolonged stay in orbit a step by step normalisation of the swimming behaviour took place in the fish. After return to 1g earth conditions no somersaulting or looping could be detected concerning the fish, but still slow and disorientated movements as compared to controls occurred. The fish larvae adapted to earth gravity within 3-5 days. Fish seem to be in a distinct early developmental stages extreme sensitive and adaptable to altered gravity; However, elder fish either do not react or show compensatory behaviour e.g. escape reactions.     

基于改进STI方法的外源磁场垂直分量动力非平稳性分析

Space Time-Index（STI）方法是一种验证时间序列中是否存在非平稳性的图示方法. 利用改进的STI方法可以定量分析外源磁场垂直分量z的非平稳性特征. 以不同地磁指数（K=0,2,4,6）、不同Lloyd季节和昼夜外源磁场z分量为对象进行对比分析. 结果表明,改进的STI方法能够有效检验外源磁场的非平稳特性,且z分量为非平稳时间序列;不同K指数的z分量分析表明,随着K指数的增加,z分量的相空间分布越来越不均匀,时间演化特征越来越复杂;不同Lloyd季节的分析表明,各季节的STI图较为相似,但随着日地距离的减小,z分量时间演化特征的复杂性增强,呈现出一定季节变化特征;对昼夜变化的分析可知,夜晚z分量STI图的波动性比白天要强,昼夜变化特征较为明显.      

Insects as test systems for assessing the potential role of microgravity in biological development and evolution.

Gravity and radiation are undoubtedly the two major environmental factors altered in space. Gravity is a weak force, which creates a permanent potential field acting on the mass of biological systems and their cellular components, strongly reduced in space flights. Developmental systems, particularly at very early stages, provide the larger cellular compartments known, where the effects of alterations in the size of the gravity vector on living organisms can be more effectively tested. The insects, one of the more highly evolved classes of animals in which early development occurs in a syncytial embryo, are systems particularly well suited to test these effects and the specific developmental mechanisms affected. Furthermore, they share some basic features such as small size, short life cycles, relatively high radio-resistance, etc. and show a diversity of developmental strategies and tempos advantageous in experiments of this type in space. Drosophila melanogaster, the current biological paradigm to study development, with so much genetic and evolutionary background available, is clearly the reference organism for these studies. The current evidence on the effects of the physical parameters altered in space flights on insect development indicate a surprising correlation between effects seen on the fast developing and relatively small Drosophila embryo and the more slowly developing and large Carausius morosus system. In relation to the issue of the importance of developmental and environmental constraints in biological evolution, still the missing link in current evolutionary thinking, insects and space facilities for long-term experiments could provide useful experimental settings where to critically assess how development and evolution may be interconnected. Finally, it has to be pointed out that since there are experimental data indicating a possible synergism between microgravity and space radiation, possible effects of space radiation should be taken into account in the planning and evaluation of experiments designed to test the potential role of microgravity on biological developmental and evolution.     

An ethical approach to planetary protection

What hazards might biological contamination pose to planets, comets and other celestial bodies visited by probes launched from Earth? What hazards might returning probes pose to Earth and its inhabitants? What should be considered an acceptable level of risk? What technologies, procedures and constraints should be applied? What sort of attitude has to be chosen concerning human crews, who themselves could become both contaminated victims and contaminating agents? The vast issue of planetary protection must, more than ever, spark ethical debate. Space treaty, COSPAR recommendations offer borders and context for this reflection, which has to be introduced in the actual humanist: never has been anthropocentrism so practical and concerned, in the same time, by the next generations, because of the historical character of life. At least an ethics of risk is necessary (far from the myth of zero-risk) for all the three types of contamination: other celestial bodies (forward contamination), Earth (backward contamination) and astronauts.     

Biological life support for manned missions by ESA.

The anticipated evolution of life support technologies for ESA, considering both the complementary life support system requirements and the missions' characteristics, is presented. Based on these results, promising biological life support technologies for manned space missions have been selected by ESA either for their intrinsic ability and performance in effecting specific tasks for atmosphere-, water-, waste-management versus physico-chemical alternatives and/or for longer-term application to a more ecological concept (CES) focusing ultimately on food production. Actual status and plan for terrestrial and space testing of biological life support presented focusing on the "task specific" decontamination technology of the Biological Air Filter (BAF), and on food reprocessing technologies from biodegradable wastes with the MELISSA microbial ecosystem.     

An alternative approach to solar system exploration providing safety of human mission to Mars.

For systematic human Mars exploration, meeting crew safety requirements, it seems perspective to assemble into a spacecraft: an electrical rocket, a well-shielded long-term life support system, and a manipulator-robots operating in combined "presence effect" and "master-slave" mode. The electrical spacecraft would carry humans to the orbit of Mars, providing short distance (and low signal time delay) between operator and robot-manipulators, which are landed on the surface of the planet. Long-term hybrid biological and physical/chemical LSS could provide environment supporting human health and well being. Robot-manipulators operating in "presence effect" and "master-slave" mode exclude necessity of human landing on Martian surface decreasing the level of risk for crew. Since crewmen would not have direct contact with the Martian environment then the problem of mutual biological protection is essentially reduced. Lightweight robot-manipulators, without heavy life support systems and without the necessity of returning to the mother vessel, could be sent as scouts to different places on the planet surface, scanning the most interesting for exobiological research site. Some approximate estimations of electric spacecraft, long-term hybrid LSS, radiation protection and mission parameters are conducted and discussed.     

Weibull分布更新函数的指数近似算法

针对Weibull分布的更新函数较难确定的问题,研究了在平均寿命相等情况下指数分布与Weibull分布之间的贴近性.在此基础上,提出利用指数分布的更新函数模型计算Weibull分布的更新函数,能够比较方便有效地得到近似解.通过实例计算,分别比较了指数方法(直接利用指数分布的更新函数)、线性加权模型以及几何加权模型等三种方法的精度.结果表明:当时间较短时,线性加权和几何加权模型比指数方法精确度有所提高;当时间较长时,几何加权模型的精度较高.利用该结论能够为工程应用提供方便.     

Life on Mars? II. Physical restrictions.

The primary physical factors important to life's evolution on a planet include its temperature, pressure and radiation regimes. Temperature and pressure regulate the presence and duration of liquid water on the surface of Mars. The prolonged presence of liquid water is essential for the evolution and sustained presence of life on a planet. It has been postulated that Mars has always been a cold dry planet; it has also been postulated that early mars possessed a dense atmosphere of CO2 (> or = 1 bar) and sufficient water to cut large channels across its surface. The degree to which either of these postulates is true correlates with the suitability of Mars for life's evolution. Although radiation can destroy living systems, the high fluxes of UV radiation on the martian surface do not necessarily stop the origin and early evolution of life. The probability for life to have arisen and evolved to a significant degree on Mars, based on the postulated ranges of early martian physical factors, is almost solely related to the probability of liquid water existing on the planet for at least hundreds of millions to billions of years.     

Biological nitrogen fixation under primordial Martian partial pressures of dinitrogen.

Early Earth and early Mars were similar enough such that past geochemical and climatic conditions on Mars may have also been favorable for the origin of life. However, one of the most striking differences between the two planets was the low partial pressure of dinitrogen (pN2) on early Mars (18 mb). On Earth, nitrogen is a key biological element and in many ecosystems the low availability of fixed nitrogen compounds is the main factor limiting growth. Biological fixation of dinitrogen on Earth is a crucial source of fixed nitrogen. Could the low availability of dinitrogen in the primordial Martian atmosphere have prevented the existence, or evolution of Martian microbiota? Azotobacter vinelandii and Azomonas agilis were grown in nitrogen free synthetic medium under various partial pressures of dinitrogen ranging from 780-0 mb (total atmosphere=1 bar). Below 400 mb the biomass, cell number, and growth rate decreased with decreasing pN2. Both microorganisms were capable of growth at a pN2 as low as 5 mb, but no growth was observed at a pN2 < or = 1 mb. The data appear to indicate that biological nitrogen fixation could have occurred on primordial Mars (pN2=18 mb) making it possible for a biotic system to have played a role in the Martian nitrogen cycle. It is possible that nitrogen may have played a key role in the early evolution of life on Mars, and that later a lack of available nitrogen on that planet (currently, pN2=0.2 mb) may have been involved in its subsequent extinction.     

Head and neck tumors after energetic proton irradiation in rats.

This is a two-year progress report on a life span dose-response study of brain tumor risk at moderate to high doses of energetic protons. It was initiated because a joint NASA/USAF life span study of rhesus monkeys that were irradiated with 55-MeV protons (average surface dose, 3.5 Gy) indicated that the incidence of brain tumors per unit surface absorbed dose was over 19 times that of the human tinea capitis patients whose heads were exposed to 100 kv x-rays. Examination of those rats that died in the two-year interval after irradiation of the head revealed a linear dose-response for total head and neck tumor incidence in the dose range of 0-8.5 Gy. The exposed rats had a greater incidence of pituitary chromophobe adenomas, epithelial and mesothelial cell tumors than the unexposed controls but the excessive occurrence of malignant gliomas that was observed in the monkeys was absent in the rats. The estimated dose required to double the number of all types of head and neck tumors was 5.2 Gy. The highest dose, 18 Gy, resulted in high mortality due to obstructive squamous metaplasia at less than 50 weeks, prompting a new study of the relative biological effectiveness of high energy protons in producing this lesion.     

The relation of solar flares to the evolution and proper motions of magnetic fields

The second Action Interval of the FBS coincided with an extended period of gradual evolution in a large complex of activity which served as the target for a coordinated space-ground study. The complex produced a multitude of subflares, half of which were clustered around just a few sites, each with a distinctive magnetic character. The essential flare-producing conditions at these preferred sites were preserved for many hours, even days, despite disruptions by flares and despite the eroding effects that accompany the disintegration of sunspot groups. Three preferred sites were active for the entire Interval, 22–27 May 1980. A comparison of flaring with non-flaring sites which also contained strong concentrations of flux demonstrates the importance of magnetic complexity, flux emergence, and motions at the photospheric level. The most energetic events by far, a chain of five closely homologous flares, erupted within 13 hours at a site where all these factors were conspicuously combined. The incessant activity preceding and during these flares of the fine chromospheric fibrils that covered and surrounded this particularly energetic site indicates reconfiguration of flux tubes in the chromosphere in a matter of minutes. These rapid (2–5 minutes), small (～10 arc-sec) changes are identified with emerging flux and with pores moving rapidly (≥200 m/s) very close to a magnetic neutral line.