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This chapter provides up-to-date coverage on the geophysical, chemical, and biological properties of the lakes that lie beneath the Antarctic ice cap (subglacial lakes). There are at least 150 lakes beneath this ice cap and many may be connected by networks of subglacial streams and rivers. The most well known of these lakes is Lake Vostok. Recent evidence indicates that subglacial lakes may initiate and maintain rapid ice flow, and should be considered in ice sheet mass balance assessments. The discovery of viable organisms in subglacial environments demonstrates that life has radiated into all aquatic habitats on the planet. Sub-glacial liquid environments offer an exciting frontier. Their study will provide an improved understanding of the coupling of geological, glaciological, and biological processes in the polar zones.

This chapter examines three limit biologies that theorize what life was—that is, they declare the possible end of “life”: Artificial Life, marine microbiology, and astrobiology. Artificial Life is a genre of theoretical biology that flourished most vigorously in the 1990s and sought to model living things in the medium of computer simulation. Marine microbiology is a field that has as its object of study the world's tiniest, most abundant, and metabolically extreme ocean creatures, including microbes at deep-sea volcanoes. Astrobiology is the study of life as it might exist on other worlds. The chapter argues that the conceptual trouble bedeviling “life” is shadowed by worries about what form “theory” might take in natural and social analysis these days. The emphasis is on how accounts of life forms in biology and ideas about social and cultural forms of life inform and deform one another.

This chapter examines the project of astrobiology and its object, the “signature of life,” by drawing on the work of Hillel Schwartz, particularly his writing on time in Century's End, on duplication in The Culture of the Copy, and on signification in “De-Signing.” Schwartz's work can provide a fresh angle on the doublings, redoublings, definitions, and redefinitions at the heart of astrobiology's quest for extraterrestrial life. His crabwise approach offers provocative paratactical techniques for traversing the networks of association, acknowledged and unacknowledged, that support the concept of the signature of life. The chapter first considers the Search for Extraterrestrial Intelligence (SETI), through the optic of Schwartz's writings on copying and his work on noise before discussing astrobiology's notion of the signature of life. It also offers suggestions for thwarting the overreaching of the theoretical impulse in both life sciences and humanities.

This chapter introduces the field of microbial ecology and some terms used in the rest of the book. Microbial ecology, which is the study of microbes in natural environments, is important for several reasons. Although most are beneficial, some microbes cause diseases of higher plants and animals in aquatic environments and on land. Microbes are also important because they are directly or indirectly responsible for the food we eat. They degrade pesticides and other pollutants contaminating natural environments. Finally, microbes are important in another ‘pollution’ problem: the increase in greenhouse gases such as carbon dioxide and methane in the atmosphere. Because microbes are crucial for many biogeochemical processes, the field of microbial ecology is crucial for understanding the effect of greenhouse gases on the biosphere and for predicting the impact of climate change on aquatic and terrestrial ecosystems. Even if the problem of climate change was solved, microbes would be fascinating to study because of the weird and wonderful things they do. The chapter ends by pointing out the difficulties in isolating and cultivating microbes in the lab. In many environments, 〈 1 per cent of all bacteria and probably other microbes can be grown in the lab. The cultivation problem has many ramifications for identifying especially viruses, bacteria, and archaea in natural environments and for connecting up taxonomic information with biogeochemical processes.

This chapter considers and rejects traditional spaceflight rationales, accenting the insubstantial evidence that is usually offered in their support. It uses regression analyses and public opinion data to show that spaceflight activities do not have a clear impact on either STEM degree conferral rates or overall scientific literacy within the United States. Next, it uses public opinion data to show that the general public is not especially interested in astrobiology or in the scientific search for extraterrestrial life. It also uses genetics and anthropological research to show that there is no innate human biological compulsion to explore space. Finally, it describes and criticizes the “space frontier” metaphor as well as basic arguments for space resource exploitation and space settlement.

This chapter argues that the scope of planetary protection policies should be expanded to include all potential sites of interest to space science. It begins by providing an overview of planetary protection policies and their history. This is followed by discussions of Charles Cockell’s views on the ethics of microbial life, Holmes Rolston’s views on the preservation of natural value in the solar system, and Tony Milligan’s views on respecting natural integrity in space. It argues that each view unnecessarily understates the scope of science’s interest in the protection of space environments. Since every space environment is virtually unexplored, as a precautionary default it should be assumed that a space environment is of interest to science (and thus worth protecting) until otherwise proven.

This chapter briefly reviews some the challenges encountered in the search for extraterrestrial life. So far, no signs of extraterrestrial life have been found. The search started with radio telescopes, looking for technology-based civilizations, but new strategies have emerged that take on the primary challenges in this search: the enormous distances to exoplanets and the question of the true nature of life. The author outlines the development of new tools for the search, and why the present focus is on Earth-sized exoplanets with a potential for liquid water on their surfaces. Not having been visited by an alien civilization presents us with a paradox: if life develops as quickly elsewhere as on Earth, then why have we not been contacted? Is the speed of light too slow to cross interstellar distances, is life intrinsically rare, or should we conclude that civilizations are intrinsically short-lived?

The goal of this chapter is to introduce the field of microbial ecology and some terms used in the rest of the book. Microbial ecology, which is the study of microbes in natural environments, is important for several reasons. Although most are beneficial, some microbes cause diseases of higher plants and animals in aquatic environments and on land. Microbes are also important because they are directly or indirectly responsible for the food we eat. They degrade pesticides and other pollutants contaminating natural environments. Finally, they are important in another “pollution” problem: the increase in greenhouse gases such as carbon dioxide and methane in the atmosphere. Because microbes are crucial for many biogeochemical processes, the field of microbial ecology is crucial for understanding the effect of greenhouse gases on the biosphere and for predicting the impact of climate change on aquatic and terrestrial ecosystems. Even if the problem of climate change were solved, microbes would be fascinating to study because of the weird and wonderful things they do. The chapter ends by pointing out the difficulties in isolating and cultivating microbes in the laboratory. In many environments, less than one percent of all bacteria and other microbes can be grown in the laboratory. The cultivation problem has many ramifications for identifying especially viruses, bacteria, and archaea in natural environments, and for connecting up taxonomic information with biogeochemical processes.

This chapter studies the concept of an extremophile. In the 1970s, R. D. MacElroy coined the term “extremophile” to describe microorganisms that thrive under extreme conditions. This hybrid word transliterates to “love of extremes” and has been studied as a straightforward concept ever since. The chapter then delineates five different ways to think about extremophiles, concluding that the concept is especially prone to the vagueness and arbitrariness that plague other biological categories, since it unavoidably involves debatable assumptions about life's nature and limits. These five concepts are, briefly, human-centric, at the edge of life's habitation of morphospace, by appeal to statistical rarity, described by objective limits, and at the limits of impossibility for metabolic processes. Importantly, these concepts have coexisted, unacknowledged and conflated, for decades. Confusion threatens to follow from the wildly varied inclusion or exclusion of organisms as extremophiles depending on the concept used. Under some conceptions, entire kinds of extremophiles become meaningless. Ultimately, since people's understanding of how life works is shaped by what people take to be its extremes, clarifying extremophily is key for many large-scale projects in biology, biotechnology, and astrobiology.

This chapter discusses how the scientific search for evidence of extraterrestrial life has affected people's conception of the terrestrial biosphere. Austrian geologist Eduard Suess originated the term “biosphere” in 1875, describing Earth's biosphere as the area of the planet that supports life. With a deeper understanding of the history and nature of the terrestrial biosphere, the community of scientists engaged in space science and exploration recognizes the possibility of other biospheres beyond Earth. As a result, the quest to find evidence of extraterrestrial life has affected people's conception of the biosphere, the way they think about their home planet and their place on it, and their perspective on the possibility of extraterrestrial biospheres nearby and far away. Indeed, astrobiology, planetary exploration, and exoplanet science have made significant contributions to this changing understanding.

This chapter addresses a sociological question that has largely been ignored: How much does the public care about life in space? It argues that there is no clear evidence of widespread support in the United States for the scientific search for extraterrestrial life. First, a comparison with U.S. views on evolution suggests that many religious individuals would be opposed to the search. Second, a comparison with U.S. views on space exploration suggests that a large majority of the public would be unwilling to support increased funding for the search. Finally, a review of existing surveys on the public's views about astrobiology suggests that little is known about how the public frames the search for extraterrestrial life. This makes it difficult to draw any decisive conclusions about the purported universal appeal of astrobiology.

This introductory chapter provides an overview of the exploration of astrobiology. While new, astrobiology's recent success has been nothing short of amazing. In just the past 25 years, scientists have learned that the building blocks of life are found basically everywhere in the universe; that getting these building blocks to engage in the kinds of complex chemistry people associate with life is far easier than people used to think; and that planets where life could potentially evolve are extremely common. Nevertheless, scientists from a variety of fields are just beginning to address the many questions raised by the real possibility of life on other planets. Relatively little research on the broader social and conceptual aspects of astrobiology has been undertaken by scholars outside the small community of space scientists. However, a fertile field awaits early adopters from other disciplines, with many profound and largely unexplored questions waiting to be addressed by relevant experts. Some of these research questions fall squarely within traditional humanities, while others span the boundary between empirical science and other fields.

This chapter traces the history of the search for life in the universe, from the ancient Greek atomists to the emergence of modern astrobiology. The idea of inhabited worlds dates back at least to the ancient Greeks and was rationally discussed as a part of natural philosophy, mainly in the context of cosmological worldviews. If cosmological worldviews gave birth to the idea of extraterrestrial life, then philosophy and literature, in their traditional role of examining the human condition, explored the ramifications of the idea borne of that cosmological context. Interest in astrobiology and society in its broadest sense dates back at least a quarter century to the days when NASA was planning its Search for Extraterrestrial Intelligence (SETI) program. Today, astrobiology is a thriving enterprise around the world and the societal aspects are becoming an integral part of it.

This chapter explores the concept of life across traditions, from science to philosophy to theology. The term “life” covers at least three constellations of meaning or life-concepts: biological life, internal life, and rational life. Biological life shares traits with all cellular life on Earth (archaea, eubacteria, and eukarya). Internal or conscious life shares subjective interiority with humans. Rational life shares intellect with all minds that can distinguish truth from non-truth. These three lives possess different origins, extents, and futures. The chapter then identifies three distinct “hard problems of life” relating to the origin and extent of biological organization, consciousness, and reason: moving from non-life to life, from life to sentience, and from sentience to rationality. The Drake equation, the Fermi paradox, and the anthropic principle provide concrete examples in astrobiology.

This chapter argues that the concept of “life” is used in several rather distinct ways: sometimes as an all-or-nothing phenomenon and other times as a matter of degree; sometimes referring to individual organisms and other times to communities; sometimes based on specific chemistries and other times on functions. In contrast to biologists in general, astrobiologists cannot take the status of their subject matter as living or nonliving for granted. There are at least two reasons to think astrobiologists need an understanding of what counts as life. The first is to set search criteria for finding “life as we don’t know it” in the universe. The second is to set success conditions conducive to agreement about when life has been found and when it has not. In addition to particular cases like the recent Mars finding by NASA, the meaning of “life” figures into a broader agenda in astrobiology: looking for biosignatures.

This chapter draws inspiration from statistical physics to describe a statistical category that can be termed the “living state.” References to a living state can be found throughout origin of life and astrobiology science. Some researchers have used the concept of the living state to explicitly place biological phenomena within the epistemological scope of statistical physics. Within this framework, biological phenomena at a given scale of organization are explained and understood by appealing to the statistical properties of the dynamics of the smaller and larger scales. This is analogous to how distinct states of matter are understood by appealing to the statistical properties of atoms, with the important distinction that statistical physicists have historically not included constraints from larger levels of organization, which are essential in determining the properties of living systems. This conception of the living state may enable astrobiologists to integrate progress from different disciplinary perspectives into a quantitative theory of life.