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Executive Summary
Pages 1-4

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From page 1...
... Earth abundantly displays life that uses solar, geothermal, and chemical energy to maintain thermodynamic disequilibria, covalent bonds between carbon, water as the liquid, and DNA as a molecular system to support Darwinian evolution. Life with those characteristics can be found wherever water and energy are available.
From page 2...
... Finally, the committee considered more exotic solutions to problems that must be solved to create the emergent properties that we agree characterize life. The committee found that using thermal and chemical energy to maintain thermodynamic disequilibria, covalent bonds between carbon atoms, water as the liquid, and DNA as a molecular system to support Darwinian evolution is not the only way to create phenomena that would be recognized as life.
From page 3...
... Recommendation . The National Aeronautics and Space Administration and the National Science Foundation should support these kinds of field research: • A search for remnants of an RNA world in extant extremophiles that are deeply rooted in the phylogenetic tree of life; • A search for organisms with novel metabolic and bioenergetic pathways, particularly pathways involved in carbon dioxide and carbon monoxide reduction and methane oxidation coupled with electron acceptors other than oxygen; • A search for organisms that derive some of their catalytic activity from minerals rather than protein enzymes; • A search for organisms from environments that are limited in key nutrients, including phosphorus and iron, and determination of whether they can substitute other elements, such as arsenic, for phosphorus; • A search for life that can extract essential nutrients -- such as phosphorus, iron, and other metals -- from rocks, such as pyrites and apatite; • A search for anomalous gene sequences in conserved genes, particularly DNA- and RNA-modifying genes; • Study of the resistance of microorganisms that form biofilms on minerals to the harsh conditions of interplanetary transport; and • A search for life that stores its heredity in chemicals other than nucleic acids.
From page 4...
... that arrived via material ejected from Earth (or vice versa) and life that emerged on another body independently of life on Earth; • Inclusion in missions planned for Mars of instruments that detect lighter atoms, simple organic functional groups, and organic carbon to help distinguish between "replicator-first" and "metabolism-first" theories of the origin of life; similar considerations should guide inclusion of small-organic-molecule detectors that could function on the surfaces of Europa, Enceladus, and Titan; and • Consideration, in view of the discovery of evidence of liquid water-ammonia eutectics on Titan and active water geysers on Saturn's moon Enceladus, of whether the planned missions to the solar system should be reordered to permit returning to Titan or Enceladus earlier than is now scheduled.


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