On average, it takes about five billion years for the biogenic elements pro- 

 duced within one star to become gravitationally bound within a later-generation 

 star. Along the way from one stellar interior to the next, the biogenic elements 

 cycle in and out of several types of environments within the interstellar medium. 

 Here they undergo chemical and isotopic alterations and suffer a large number of 

 near misses in the star-formation game. One important type of interstellar envi- 

 ronment is the giant molecular cloud. These are observed to be active nurseries 

 for stars being born at this time. Each such cloud may have a mass of up to 

 1 6 M @ , densities ranging from 1 4 to 1 6 cm -3 , and cool temperatures, ~1 to 

 50 K. By the time it is finally dispersed (in part by the energetics of star forma- 

 tion), such a cloud will have converted only about 100 M^ into stars. During 

 their lifetimes the giant molecular clouds serve as very effective molecule and 

 dust factories powered by radiation fields, hydrodynamical energies of the 

 embedded newly forming stars, and interstellar cosmic ray flux. More than 

 70 organic molecules have been detected in interstellar space, mostly within 

 giant molecular clouds, and the unidentified spectral lines resulting from radio 

 observations indicate that the list is incomplete. 



Within the giant molecular cloud complexes it is clear that H 2 is formed on 

 the surface of dust grains, but the composition and origin of the dust are much 

 debated. Dust is formed when the enriched elemental gas in the outer layers of 

 an evolving star is blown off in a stellar wind. Subsequent cooling of the wind 

 leads to condensation of grains far from the stellar surface. Grains are also 

 formed in the winds that blow off newly formed stars; in the novae outbursts of 

 dying stars; perhaps in the rapidly cooling regions behind shock waves propagat- 

 ing throughout the molecular clouds; and perhaps, too, in the cooling ejecta of 

 supernovae, whose strong shock waves also destroy preexisting dust grains 

 throughout a large volume of the interstellar medium. This dust may be com- 

 posed of carbon and other biogenic elements if it condensed in the wind from a 

 giant carbon star, or it may perhaps provide a catalytic surface for the transfor- 

 mation of the biogenic elements and compounds into ever more complex organic 

 molecules within the molecular clouds. The dust in molecular clouds is impor- 

 tant as a shield against ultraviolet radiation without doubt, but its composition 

 and the exact role it plays in the cloud chemistry beyond the formation of H 2 

 is still questioned. Even in the event that the dust plays no active role in the gas- 

 phase chemistry, it may still be of particular importance to exobiology if it pro- 

 vided a vehicle for inclusion of the biogenic elements into the protosolar nebula 

 in a highly processed form. There is a growing body of evidence, based on iso- 

 topic anomalies, that some interstellar dust has survived its introduction into the 

 nebula. Whether manufactured on the surface of the grains or not, some organic 

 molecules do coat solid grains of dust and reveal themselves by the vibrational 

 spectra observed in the infrared. 



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