FIGURE 2.13 Some of the many forms that carbon might take in interstellar molecules. SOURCE: P. Ehrenfreund and S.B. Charnley, Organic molecules in the interstellar medium, comets, and meteorites: A voyage from dark clouds to the early Earth, Annual Review of Astronomy and Astrophysics 38:427-483, 2000.

in understanding where and in what form are the raw materials for life with which any given planetary system might be endowed (Figure 2.14).

To what extent does the potential for life change through the galaxy over its history? We do not understand the ultimate levels of complexity achieved by organic chemistry in astrophysical environments, for example, whether complex information-carrying polymers like ribonucleic acid might be produced before planet formation. Study at ever more powerful spectral and spatial resolution of astrophysical environments in which organic molecules occur and evolve is necessary to trace the full potential of organic chemistry to produce molecules of relevance to life, through as much of the galaxy as is possible. Such environments include the interstellar medium, molecular clouds, protoplanetary disks, transition and debris disks, and especially planetary atmospheres. And this, in turn, brings us full circle in our tour of the modern understanding of the cosmos: the exotic phenomena of the earliest moments of the cosmos set the stage for a physical reality in which stars, planets, and life—we—could exist.