This finding invokes many intriguing questions, regarding how long microorganisms can survive and specifically, how halophiles could stay alive for million years in their small, saline prisons. These observations do indeed imply that some microorganisms may have eternal life, at least in relation to the brief lifetime of most plants and animals. Igneous rocks are the predominant solid constituents of the earth, formed through cooling of molten or partly molten material at or beneath the earth's surface. These rocks are penetrated by humans for a variety of purposes such as mining for metals, the extraction of groundwater and the building of tunnels and vaults for communication, transport, defence, storage, deposition and waste disposal.
The concept of underground storage of hazardous wastes is commonly applied to materials that are impossible to transform to a non-hazardous form. One group of such materials is the toxic metals, especially heavy metals and radionuclides. The disposal concepts vary from country to country, but igneous rocks are commonly in target for countries with access to these types of geological structures.
Deposition of long-lived hazardous wastes requires extremely good knowledge about the igneous rock environment to be used as a host. Particularly the nuclear waste industry invests large sums in research on the safe underground disposal of all types of radioactive wastes [ 37 ]. Early studies in the Swedish long-term nuclear waste disposal research programme on subterranean microbiology revealed previously unknown microbial ecosystems in igneous rock aquifers at depths exceeding m [ 38 ].
This discovery triggered a thorough exploration of the subterranean biosphere in the aquifers of the Fennoscandian Baltic Shield [ 39 ]. Similarly, the Canadian radioactive waste disposal programme has stimulated investigations of microorganisms in deep igneous rock aquifers of the Canadian Shield [ 40 ]. Other investigations examined the potential risk of radionuclide migration caused by microorganisms able to survive in the deep groundwater systems [ 41 ]. It soon became apparent that microbial communities exist in most, if not all, deep aquifers [ 38 ].
Attention was then shifted to assay the activity potential of these microorganisms using radiotracer methods [ 42—45 ]. This work has also revealed several hitherto unknown microbial species adapted to life in igneous rock aquifers [ 48—50 ]. The repeated observations of autotrophic, hydrogen-dependent microorganisms in the deep aquifers imply that hydrogen may be an important electron and energy source and carbon dioxide an important carbon source in deep subsurface ecosystems. Therefore, a model has been proposed of a hydrogen-driven biosphere in deep igneous rock aquifers in the Fennoscandian Shield [ 39 ].
A similar model has been suggested for deep basalt aquifers [ 52 ]. The organisms at the base of these ecosystems are assumed to be autotrophic acetogens capable of reacting hydrogen with carbon dioxide to produce acetate, autotrophic methanogens that produce methane from hydrogen and carbon dioxide, and acetoclastic methanogens that produce methane from the acetate product of the autotrophic acetogens Fig.
All components needed for the life cycle in Fig. Consequently, the model is supported by the qualitative data obtained so far. Ideally, the next step will be to obtain quantitative data, which would require very sensitive experimental conditions, because of the very slow metabolic rates that are expected under non-disturbed conditions.
The central question in such an experimental endeavour is whether or not in situ hydrogen-driven microbial chemolithoautotrophic activities at depth are in balance with estimated renewal rates of hydrogen. An indisputable positive answer to this question is crucial for the unequivocal confirmation of a deep hydrogen-driven biosphere. The deep hydrogen-driven biosphere hypothesis, illustrated by its carbon cycle. At relevant temperature and water availability conditions, intraterrestrial microorganisms are capable of performing a life cycle that is independent of sun-driven ecosystems.
Hydrogen and carbon dioxide from the deep crust of the earth are used as energy and carbon sources. Caves may provide the link between surface and subsurface environments. The cave environment varies tremendously. This cave is therefore a good example of an intraterrestrial cave environment. Allochthonous organic input to the cave is limited due to the depth, but bacterial and fungal colonisation is relatively extensive [ 53 ]. Various points of evidence suggest that autotrophic bacteria are present in the ceiling-bound residues and could act as primary producers in a unique subterranean microbial food chain.
Because other major sources of organic matter have not been detected, it is suggested that these bacteria provide requisite organic matter to the known heterotrophic bacteria and fungi in the residues. The cave-wide bacterial and fungal distribution, the large volumes of corrosion residues and the presence of ancient bacterial filaments in unusual calcite speleothems biothems attest to the apparent longevity of microbial occupation in this cave.
More research should be invested in this and other caves to reveal the ecology and the biogeochemistry of cave ecosystems. The search for the maximum depths for life in various intraterrestrial environments will probably always be one major desire in the exploration of deep life. Knowing more about these limits to life within our planet will enable more precise calculations of the total amount of intraterrestrial organisms.
Therefore, these deep crustal environments are relevant targets for the search of the maximum temperature for life. A paper on anaerobic degradation and methane production from long chain alkanes by a consortium of microorganisms was recently published [ 54 ]. A team of seven different microorganisms were observed to crack the hydrocarbon, to produce methane and carbon dioxide and also to expel hydrogen sulfide. This is an encouraging result for those who believe that any catabolic reaction that can be linked to oxygen as the electron acceptor, may also occur in the absence of oxygen, albeit slower and as a result of collaboration between species.
The experiment showing anaerobic degradation of alkanes continued for almost two years before conclusive results were obtained. One implication deduced from these results is that intraterrestrial microbes play in a very different league from those in well-fed, aerobic, pure cultures.
Patience, a great deal of time and advanced culturing methods will be required for successful exploration of the metabolic activities of intraterrestrial microbial communities.
Most deep environments contain methane in varying concentrations. Methane oxidation in aerobic environments is well documented and very widespread on the planet. As yet, there exists no microorganism, or community of microorganisms, in culture that oxidises methane under anaerobic conditions, although much indirect evidence for the occurrence of this process in nature has been published see, e.
If a metabolic process for anaerobic methane oxidation can be demonstrated, then a tremendous source of energy and carbon will become available for models of how intraterrestrial life is fuelled. The theory of a deep biosphere driven by hydrogen generated in deep geological strata Fig. There are at least six possible processes whereby crustal hydrogen is generated [ 56 ]:. The reaction between dissolved gases in the carbon—hydrogen—oxygen—sulfur system in magmas, especially in those with basaltic affinities.
Radiolysis of water by radioactive isotopes of uranium and thorium and their daughter isotopes, and potassium. It is important to explore the scale of these processes and the rates at which the produced hydrogen is becoming available for deep microbial ecosystems. The idea, in conclusion, that life originated on the surface of our planet, where it was strongly dependent on a hypothetical primordial soup, has recently come up against strong competition.
Today there are several suggestions that life originated in the form of a thermophilic lithotroph [ 57 ] and that the birthplace was intraterrestrial, perhaps a hydrothermal vent area [ 58 ]. Consequently it should be obvious that the search for extraterrestrial life should concentrate on samples from under the surface of other planets [ 59 ]. However, that is another topic and far too speculative for this mini-review.
Oxford University Press is a department of the University of Oxford. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide. Sign In or Create an Account. Close mobile search navigation Article navigation. Exploration of deep intraterrestrial microbial life: Abstract Intraterrestrial life has been found at depths of several thousand metres in deep sub-sea floor sediments and in the basement crust beneath the sediments.
Autotrophy , Biosphere , Groundwater , Rock , Subsurface. View large Download slide. Search for hyperhermophilic microorganisms in fluids obtained from the KTB pump test. Thermophilic, anaerobic bacteria isolated from a deep borehole in granite in Sweden. Thermodesulforhabdus norvegicus gen, sp. Organic carbon content, bacterial methanogenesis, and accumulation processes of gas hydrates in marine sediments.
Alteration of oceanic volcanic glass: Deep marine biosphere fuelled by increasing organic matter availability during burial and heating. Textural and chemical effects of bacterial activity on basaltic glass: You have to decide if you want it," Crawford declares. If you care about your startup more than you care about all those things, then go for it. But it comes with sacrifice," he says, leveling with would-be founders. Along similar lines, other entrepreneurs or more often ex-entrepreneurs have confessed that the start-up lifestyle and family life can be an impossible balance.
The effect of exposure to real-life violence on reactivity to violent videos varied by gender and only involved emotional reactions, not changes in blood pressure. Specifically, males who had been exposed to higher levels of real-life violence reported decreasing emotional distress through the viewing period, compared to increasing distress among males exposed to lower levels of real-life violence and females regardless of their exposure history a medium sized effect. These results are consistent with the hypothesized desensitization pattern of less emotional reactivity to violence among those with higher levels of exposure to real-life violence.
One explanation for the gender difference may be a greater tendency of males to develop desensitization, perhaps because they are generally exposed to more violence than females Finkelhor et al. This hypothesis is supported by reports of physiological desensitization among males but not females Kliewer ; Linz et al. Another explanation may be related to the violent scenes shown in this study depicting primarily males as victims and perpetrators of violence reflecting general gender patterns in violent movies; Smith et al.
Perhaps males were more likely to identify with the same-sex victims than females Calvert et al. Finally, it is possible that males exposed to higher levels of real-life violence were more aware of the fictitious nature of the movie violence and therefore experienced declining distress. Clearly, more research is needed to replicate and elucidate these findings. Exposure to movie violence was modestly positively correlated with exposure to real-life violence, consistent with other studies of older children and adolescents Boxer et al.
To better understand this relationship, we have examined correlations between perspective taking and the four variables that were combined to measure exposure to televised violence. However, exposure to movie violence was not related to PTSD symptoms, fantasy, diminished empathy or baseline blood pressure, providing no evidence of longer-term trauma or desensitization.
Our findings may not generalize to younger youth who may be more vulnerable and less able to distinguish between reality and fiction Wright et al. Participants reported gradually increasing emotional distress as they watched the violent movie clips, confirming the distressing nature of the movie scenes selected for use in this study. Interestingly, the same effect was observed for the nonviolent clips that showed people's lives endangered by natural phenomena tornado, waves , or vehicle crashes car and airplane crash, impending bus crash but no interpersonal violence.
Similarly, moderate elevations in blood pressure were experienced by participants viewing both types of videos, which are consistent with response to stressful stimuli in a passive viewing context Sherwood et al. Since emotional distress increased throughout the viewing period, there was no evidence of immediate desensitization. Others who found emotional desensitization to violent movies included much longer exposure, presenting full movies over 5 days Linz et al. Specifically, high levels of previous exposure to televised violence were associated with initially high 4. In contrast, those with low previous exposure to movie violence exhibited moderate initial blood pressure increase about 2.
The pattern for individuals with medium levels of exposure was consistent with our hypothesis of desensitization, involving less physiological reactivity compared to those with low levels of exposure. However, the pattern for the highly exposed group was unexpected. The initial rapid increase in SBP might reflect excitement about watching familiar movie violence, followed by quick physiological habituation, which could reflect physiological desensitization.
This pattern may represent a parallel to addiction; for instance, high frequency gamblers experience greater initial arousal than low frequency gamblers, and their arousal decreases faster during the playing period Leary and Dickerson ; Sharpe More research is needed to characterize the physiological and psychological experiences of youth who routinely consume violent media. However, exposure to real-life violence was related to emotional functioning in more complex ways than traditionally assumed. Specifically, some exposure to real-life violence was associated with higher levels of cognitive and emotional empathy than no experience with violence, suggesting that there may be some developmental benefits of experiencing limited amounts of real-life violence.
Nevertheless, at higher levels exposure to real-life violence is clearly maladaptive, as it is linked with more symptoms of trauma, including avoidance and escape to fantasy, less empathy and understanding for others, and for males also lower emotional reactivity to violence.
The combination of traumatic symptoms, escape to fantasy and low empathy are likely to contribute to difficulties in social relationships and decreased social support Beck et al. Additionally, lower empathy and emotional reactivity to violence may contribute to more violent behavior or failure to intervene as a bystander to violence Florsheim et al.
Thus, adolescents and emerging adults who have been exposed to higher levels of real-life violence would benefit from psychological interventions to help them cope with these challenging experiences and emotional sequelae. Prospective research also is needed to elucidate the long-term effects of these markers of desensitization to violence. The present findings also have implications for future research on exposure to violence. Most importantly, the results demonstrate that the relationships between exposure to violence and some aspects of emotional and physiological functioning are not simply linear, as typically studied, but follow more complex curvilinear patterns.
The presence of such curvilinear patterns may help explain previous null or inconsistent findings, as we showed for empathy. Thus, to more accurately represent the role of exposure to violence in adaptive and maladaptive outcomes, future research should incorporate more complex, nonlinear models.
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In addition, research should continue to systematically evaluate gender differences in the effects of exposure to violence. The findings of this study need to be interpreted in the context of its limitations. The cross-sectional design of the study does not permit causal inferences about the relationships between exposure to violence and PTSD symptoms, empathy, fantasy and baseline physiological functioning. Stronger inferences could be drawn from experimental studies that manipulate exposure to real-life or movie violence, longitudinal studies that track exposure to violence, emotional functioning and physiological arousal over time, and quasi-experimental studies that compare individuals differentially exposed to random violence e.
Another limitation of this study is the exclusion of video game violence, which has been linked more extensively with emotional and physiological desensitization Carnagey et al. This exclusion was done on purpose to allow a focus on more passive forms of violent media exposure and to parallel the exposure to violent movie clips in the lab.
As suggested by some research Funk et al. More research is needed to directly compare these different forms of violent media, particularly in experimental studies. Our assessment of emotional and physiological functioning also was somewhat limited. Future studies would benefit from including measures of more generalized emotional distress e. Similarly, the inclusion of additional physiological measures with well-elaborated links to affective processing mechanisms and e.
Finally, neuroimaging is an additional promising avenue for better understanding of the impact of exposure to violence on cognitions, emotions and behavior Bartholow et al. Although our sample of college students was racially diverse, the results may not generalize to young adults not attending college, males who were somewhat underrepresented in the sample , and high-risk or clinical populations. The reactivity analyses were limited by smaller sample size half of the original sample which decreased power to detect complex interactive effects of smaller magnitude and those involving gender due to the gender imbalance.
The studied relationships may also vary as a function of development and should be examined in studies with younger youth. Given the high prevalence of exposure to violence that youth experience in both real-life and media and frequently voiced concerns about youth becoming desensitized to violence Fanti and Avraamides ; Finkelhor et al.
While limited exposure to real-life violence appeared to have some developmental benefits in the form of higher empathy, experiencing higher levels of real-life violence was linked with maladaptive outcomes including higher trauma symptoms, escape to fantasy, and reduced empathy.
In males, higher levels of exposure to real-life violence were also associated with diminished emotional reactivity to violent videos. Thus, youth exposed to higher levels of real-life violence do show some signs of emotional desensitization involving lower empathy, and for males also decreasing distress to repeated scenes of violence. Individuals exposed to higher levels of movie violence did not demonstrate any evidence of emotional desensitization, but their blood pressure reactivity to violent videos showed more pronounced habituation effects that may indicate physiological desensitization to televised violence.
Future research should address the long-term consequences of emotional desensitization among youth exposed to high levels of real-life violence, as well as strategies to treat or prevent the development of these symptoms in these youth. SM designed the study, performed statistical analyses, and drafted the manuscript; AM designed the study, coordinated data collection, and contributed to manuscript revisions; EC contributed to study design, data analyses and manuscript revisions; RW provided guidance on study design, use of equipment for data collection, and manuscript revisions.
All authors read and approved the final manuscript. Sylvie Mrug, University of Alabama at Birmingham. Anjana Madan, University of Miami. Wright, University of North Texas. National Center for Biotechnology Information , U. Author manuscript; available in PMC May 1. Sylvie Mrug , Ph. Cook, III , Ph. Sylvie Mrug University of Alabama at Birmingham. Find articles by Sylvie Mrug. Anjana Madan University of Miami. Find articles by Anjana Madan.
Find articles by Edwin W. Wright University of North Texas. Find articles by Rex A. Author information Copyright and License information Disclaimer. Correspondence should be addressed to Dr. The publisher's final edited version of this article is available at J Youth Adolesc. See other articles in PMC that cite the published article. Abstract Youth are exposed to large amounts of violence in real life and media, which may lead to desensitization. Introduction Adolescents and emerging adults in the U. Exposure to Violence and Internalizing Problems In general, exposure to real-life violence in youth is associated with elevated internalizing symptoms, but the associations are weaker compared to links with externalizing problems and are less consistent across studies Fowler et al.
Exposure to Violence and Physiological Functioning As a disturbing and stressful experience, exposure to violence is assumed to stimulate the physiological stress response Kliewer, , which involves two physiological processes: Present Study The evidence suggests that high levels of exposure to real-life and movie violence are associated with diminished emotional distress, emotional empathy, and physiological reactivity, suggesting the presence of emotional and physiological desensitization.
Methods Participants Participants were college students recruited from introductory psychology classes at a mid-sized public university located in a metropolitan area in the Southeastern U. Measures Exposure to real-life violence The Community Experiences Questionnaire Schwartz and Proctor assessed lifetime exposure to violence. Exposure to media violence Exposure to media violence was measured with four items. Empathy Empathy was measured with three subscales of the Interpersonal Reactivity Index, a multidimensional measure of empathy Davis Procedures Participants were tested individually at a university laboratory.
Data Analysis Univariate distributions of all variables were examined; four univariate outliers were truncated to 3. Results Preliminary Analyses Descriptive statistics and correlations of all variables are presented in Table 1. Table 1 Descriptives and Correlations. Real-life violence a Media violence a Open in a separate window. Note a Mean and SD are for the original variable, but square root transformation was applied prior to all analyses.
Exposure to Violence and Reactivity to Violent Scenes Results of the multilevel models estimating the effects of exposure to violence on emotional and physiological reactivity to violent movies are presented in Table 3. Exposure to Violence and Reactivity to Nonviolent Scenes When the multilevel models were repeated for the participants randomized to view nonviolent videos, the only significant effects emerged in Step 1. Discussion Theoretical accounts and limited empirical evidence suggest that repeated exposure to violence, both in real-life and through media, produces emotional and physiological desensitization characterized by diminished emotional distress and empathy, as well as reduced emotional and physiological reactivity to further violence Krahe and Moller ; Krahe et al.
Exposure to Real-Life Violence A novel contribution to the literature on youth exposed to real-life violence is the demonstration of curvilinear relationships between exposure to violence and empathy. Exposure to Movie Violence Exposure to movie violence was modestly positively correlated with exposure to real-life violence, consistent with other studies of older children and adolescents Boxer et al. Limitations and Future Directions The findings of this study need to be interpreted in the context of its limitations.
Conclusion Given the high prevalence of exposure to violence that youth experience in both real-life and media and frequently voiced concerns about youth becoming desensitized to violence Fanti and Avraamides ; Finkelhor et al. Footnotes Author Contributions SM designed the study, performed statistical analyses, and drafted the manuscript; AM designed the study, coordinated data collection, and contributed to manuscript revisions; EC contributed to study design, data analyses and manuscript revisions; RW provided guidance on study design, use of equipment for data collection, and manuscript revisions.
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Emotional and Physiological Desensitization to Real-Life and Movie Violence
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Emotional and Physiological Desensitization to Real-Life and Movie Violence
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