Space Studies Board Annual Report 2017 (2018) / Chapter Skim
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5.10 Searching for Life Across Space and Time: Proceedings of a Workshop
5.10 Searching for Life Across Space and Time: Proceedings of a Workshop
Pages 75-88
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From page 75... ...
Each region has its own characteristic set of biosignatures and will require a different set of technologies, instruments, knowledge, and expertise to determine whether life can or does exist in each environment. This workshop is intended to foster dialogue on the best way to accomplish the goal of detecting life beyond Earth.
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From page 76... ...
HOW LIKELY IS IT THAT LIFE EXISTS BEYOND EARTH? John Baross of the University of Washington presented the first talk of the workshop on the likelihood that life exists beyond Earth.
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From page 77... ...
, the root of which was likely methanogens. Some of this evidence comes from the Loki hydrothermal vent site in the Arctic Mid-Ocean Ridge, which contained Archaean organisms called Lokiarchaea.
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From page 78... ...
An oceanic plate undergoing subduction releases this water deep in the lithosphere, which helps give rise to volcanoes and hydrothermal vent systems. Enceladus has many of the same properties as the so-called Lost City system of hydrothermal vents in the mid-Atlantic, such as detections of CO2, H2, CH4, higher-order hydrocarbons, and a high pH value.
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From page 79... ...
Moving to the importance of geology for life, another participant at the workshop asked whether having a tectonically active planet was necessary for the origin of life or whether it was only necessary for sustained habitability. Baross answered that, in his opinion, while planets and moons may be able to sustain life, a planet having had a de novo origin of life must have had plate tectonics or other, similar geophysical processes.
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From page 80... ...
: thermodynamic disequilibrium (Gibbs free energy) , an environment capable of maintaining covalent bonds (especially between C, H, and other atoms)
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From page 81... ...
Comparatively, non-photosynthetic chemical energy fluxes on Earth, such as the flux of hydrothermal vent fluids into the oxidizing ocean, amount to only about 0.006 TW in forms that can be utilized 8 Life wants carbon in an intermediate oxidation state, and on Earth, the carbon available is fully oxidized in CO . To perform this chemical 2 reduction, life needs a source of electrons, which it finds abundantly in water (in the bonds between O and H)
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From page 82... ...
He said that it is uncertain whether the ultimate limits on life are going to be found in nature or in a laboratory. A workshop participant then referred to Hoehler's discussion of the upper limits imposed on biosignature formation by energy flux and asked why he placed metabolic rates and biosynthetic rates together on the same line.
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From page 83... ...
IS LIFE A COSMIC IMPERATIVE: HOW WOULD THERMODYNAMICS FORCE LIFE INTO EXISTENCE? Eric Smith of the Santa Fe Institute discussed life as a cosmic imperative and whether the existence of a biosphere might be viewed as the ineluctable result of thermodynamics.
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From page 84... ...
The expectation that translation should be a firewall also suggests that the codon assignments of amino acids to nucleobase triplets should be arbitrary, in the sense that they could have been different than they actually are.9 The actual genetic code, however, does not really have arbitrary assignments; in information-theoretic terms, the genetic code is enormously compressible and could, for example, be represented as a decision tree for the selection 9 One can back off slightly from the assumption of arbitrariness by recognizing that coding happens with errors, and error buffering can be provided by grouping similar amino acids at related codons.
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From page 85... ...
Right: the sub-graph containing the four self-amplifying loop-autocatalytic fixation pathways that remain close to the citric acid cycle. Each pathway is drawn in a different color.
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From page 86... ...
This is true for equilibrium systems, but, dynamically, the same convergence to exponential families is possible. In the mathematical system noted above, the role played by equilibrium free energy is subsumed by an effective action associated with the trajectory, and dynamical phase transitions are the shifts of the central tendencies of macrostates.
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From page 87... ...
Audience Participation A member of the audience asked Smith whether there is enough of a free energy gradient on Enceladus and Europa for abiogenesis, which is what is needed in a metabolism-first method. Smith said that the Archean era on Earth had a longstanding disequilibrium due to having a reduced interior with a steady process of Jeans escape of hydrogen from the upper atmosphere.
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From page 88... ...
Smith responded that, in his mind, this is one of the most important questions in the origin of life. He said that a key distinction involves whether cofactors were a stepping stone towards a more structured polymer world or if they are an artifact of a polymer world that was already in place.
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