Many Chemistries Could Be Used to Build Living Systems

Bains, William

doi:10.1089/153110704323175124

Cited by 177 publications

(129 citation statements)

References 124 publications

(132 reference statements)

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“…This potentially opens up a new range for habitable planets, namely those beyond the ice line in a cryogenic habitable zone where water is frozen but other liquids such as methane and ethane are present. Although no one has yet studied the possibility of exoplanet biosignatures on cold exoplanets, research on what it takes for life in non-water liquids (Bains 2004) Biosignature research is only just beginning to unfold and seems to be fertile ground for new lines of investigation-especially with the considerable interest it draws. Nonetheless we will always be humbled by the warning that in many cases we will not be 100 percent sure of a biosignatures definite attribution to life.…”

Section: Biosignature Gasesmentioning

confidence: 99%

Exoplanet Atmospheres

Seager

Deming

2010

Annu. Rev. Astron. Astrophys.

361

320

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At the dawn of the first discovery of exoplanets orbiting sun-like stars in the mid-1990s, few believed that observations of exoplanet atmospheres would ever be possible. After the 2002 Hubble Space Telescope detection of a transiting exoplanet atmosphere, many skeptics discounted it as a one-object, one-method success. Nevertheless, the field is now firmly established, with over two dozen exoplanet atmospheres observed today. Hot Jupiters are the type of exoplanet currently most amenable to study. Highlights include: detection of molecular spectral features; observation of day-night temperature gradients; and constraints on vertical atmospheric structure. Atmospheres of giant planets far from their host stars are also being studied with direct imaging. The ultimate exoplanet goal is to answer the enigmatic and ancient question, "Are we alone?" via detection of atmospheric biosignatures. Two exciting prospects are the immediate focus on transiting super Earths orbiting in the habitable zone of M-dwarfs, and ultimately the spaceborne direct imaging of true Earth analogs.

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Section: Biosignature Gasesmentioning

confidence: 99%

Exoplanet Atmospheres

Seager

Deming

2010

Annu. Rev. Astron. Astrophys.

361

320

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“…Astrobiologists have considered the possibility of life based on solvents other than water (Clarke 2003;Bains 2004;Benner et al 2004;Ward & Baross 2007), but at present these remain purely theoretical possibilities. The search for exoplanets that might support life is thus essentially a search for rocky planets with surface temperatures allowing the presence of liquid water.…”

Section: Introductionmentioning

confidence: 99%

The thermal limits to life on Earth

Clarke

2014

International Journal of Astrobiology

121

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Living organisms on Earth are characterized by three necessary features: a set of internal instructions encoded in DNA (software), a suite of proteins and associated macromolecules providing a boundary and internal structure (hardware), and a flux of energy. In addition, they replicate themselves through reproduction, a process that renders evolutionary change inevitable in a resource-limited world. Temperature has a profound effect on all of these features, and yet life is sufficiently adaptable to be found almost everywhere water is liquid. The thermal limits to survival are well documented for many types of organisms, but the thermal limits to completion of the life cycle are much more difficult to establish, especially for organisms that inhabit thermally variable environments. Current data suggest that the thermal limits to completion of the life cycle differ between the three major domains of life, bacteria, archaea and eukaryotes. At the very highest temperatures only archaea are found with the current high-temperature limit for growth being 122°C. Bacteria can grow up to 100°C, but no eukaryote appears to be able to complete its life cycle above *60°C and most not above 40°C. The lower thermal limit for growth in bacteria, archaea, unicellular eukaryotes where ice is present appears to be set by vitrification of the cell interior, and lies at * − 20°C. Lichens appear to be able to grow down to * − 10°C. Higher plants and invertebrates living at high latitudes can survive down to * − 70°C, but the lower limit for completion of the life cycle in multicellular organisms appears to be * − 2°C.

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“…Bambach (1983Bambach ( , 1985 likewise attempted to define a space of possible ecological roles, using slightly different dimensions, and Bambach et al (2007) define a space of ecological roles for marine life. Similarly, astrobiologists debate whether life could have evolved using fundamentally different chemistry given different planetary conditions (Bains 2004). This, I would suggest, can be read as a debate about the space of possible chemistries that can support life.…”

Section: Morphospacementioning

confidence: 99%

The domain relativity of evolutionary contingency

Lewis

2018

Biol Philos

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A key issue in the philosophy of biology is evolutionary contingency, the degree to which evolutionary outcomes could have been different. Contingency is typically contrasted with evolutionary convergence, where different evolutionary pathways result in the same or similar outcomes. Convergences are given as evidence against the hypothesis that evolutionary outcomes are highly contingent. But the best available treatments of contingency do not, when read closely, produce the desired contrast with convergence. Rather, they produce a picture in which any degree of contingency is compatible with any degree of convergence. This is because convergence is the repeated production of a given outcome from different starting points, and contingency has been defined without reference to the size of the space of possible outcomes. In small spaces of possibilities, the production of repeated outcomes is almost assured. This paper presents a definition of contingency which includes this modal dimension in a way that does not reduce it to the binary notion of contingency found in standard modal logic. The result is a conception of contingency which properly contrasts with convergence, given some domain of possibilities and a measure defined over it. We should therefore not ask whether evolution is contingent or convergent simpliciter, but rather about the degree to which it is contingent or convergent in various domains, as measured in various ways. Key Words: contingency, convergence, evolution, modality Acknowledgments: This paper has been transformed several times over by excellent feedback. I am grateful for comments on a much earlier version from John Beatty and Eric Desjardins. Two quite different versions were presented to meetings of the Consortium for the History and Philosophy of Biology, both of which received helpful commentary and suggestions. Throughout the writing process I have received invaluable feedback from Denis Walsh and Philippe Huneman, as well as reading groups at the IHPST Toronto, and two anonymous reviewers. Author: Cory Travers Lewis

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Many Chemistries Could Be Used to Build Living Systems

Cited by 177 publications

References 124 publications

Exoplanet Atmospheres

Exoplanet Atmospheres

The thermal limits to life on Earth

The domain relativity of evolutionary contingency

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