5.4  Problems in Origins,

 

58

   

 5.4.1  Nucleophilic and Electrophilic Reactions Can Destroy as Well as Create,

 

59

   

 5.4.2  The Reactivity of Water Constrains Routes to Origins,

 

60

   

 5.5  Minerals as a Possible Solution to the Instability of Ribose,

 

61

   

 5.6  Minerals Involved in the Construction of Biomolecules,

 

63

   

 5.7  Small-Molecule (“Metabolism First”) Theories of Life’s Origin,

 

63

   

 5.7.1  Life Without a Replicator,

 

63

   

 5.7.2  Coupling to an Energy Source as a Driver of Chemical Self-organization,

 

64

   

 5.7.3  Significance and Implications for Astrobiology,

 

65

   

 5.8  Opportunities for Research,

 

65

   

 5.8.1  Research on Earth,

 

65

   

 5.8.2  Research in Space,

 

66

   

 5.9  References,

 

66

6

 

WHY WATER? TOWARD MORE EXOTIC HABITATS

 

69

   

 6.1  Is Water Uniquely Suited for Life?,

 

69

   

 6.2  If Not Water, Then What Solvent?,

 

71

   

 6.2.1  Polar Solvents That Are Not Water,

 

72

   

  6.2.1.1  Ammonia,

 

72

   

  6.2.1.2  Sulfuric Acid as a Possible Solvent,

 

73

   

  6.2.1.3  Formamide as a Possible Solvent,

 

74

   

 6.2.2  Nonpolar Solvents,

 

74

   

 6.2.3  Cryosolvents,

 

75

   

  6.2.3.1  Dihydrogen,

 

75

   

  6.2.3.2  Dinitrogen,

 

75

   

  6.2.3.3  Other Supercritical Cryosolvents,

 

76

   

 6.3  Still More Exotic Habitats,

 

77

   

 6.3.1  Life in the Gas Phase,

 

77

   

 6.3.2  Life in the Solid Phase,

 

77

   

 6.4  Opportunities for Research,

 

77

   

 6.5  References,

 

78

7

 

LIFE DETECTION AND BIOMARKERS

 

80

   

 7.1  Chirality as a Biomarker,

 

80

   

 7.2  Thermodynamic Relation of Metabolic Intermediates as a Biosignature,

 

82

   

 7.3  Reference,

 

83

8

 

CONCLUSIONS AND RECOMMENDATIONS.

 

84

   

 8.1  Laboratory Studies,

 

85

   

 8.2  Field Studies,

 

85

   

 8.3  Space Studies,

 

86

 

 

APPENDIXES

 

 

   

 A  Glossary

 

91

   

 B  Biographies of Committee Members and Staff

 

97



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