Sherwood Chang, Ph.D. 

 Chairf wson 



J. William Schopf, Ph.D. 



Mitchell K. Hobish, Ph.D. 



Staff Associate 



Exobiology 



Exobiology is an interdisciplinary program of scientific research conducted by the 

 NASA Life Sciences Division, located within the Office of Space Science and 

 Applications (OSSA). As its goal, the program seeks to understand the origin, 

 evolution, and distribution of life in the universe. Just as cosmic evolution implies 

 that all matter in the solar system had a common origin in a cloud of interstellar 

 gas and dust, so does biological evolution imply that all organisms arose by 

 divergence from a common ancestry. Thus, life may be viewed as the product of 

 countless changes in the form of primordial matter wrought by the processes of 

 astrophysical, cosmochemical, geological, and biological evolution that are integral 

 aspects of the development of the universe. From the knowledge gained in this 

 program, it will become possible to formulate a general theory for the natural 

 origin and evolution of life in the universe. 



Through both ground- and space-based research, the Exobiology Program seeks 

 answers to these prime questions: How did the development of the solar system 

 lead to the formation and persistence of habitable planetary' environments? How 

 did life originate on Earth? What factors operating on Earth or at large in the solar 

 system influenced the course of biological evolution from microbes to intelligence? 

 Where else may life be found in the universe? These questions hold great interest 

 for both scientists and the general public, addressing as they do the history and 

 possible uniqueness of life on Earth and prospects for its existence and detection 

 elsewhere in the galaxy. 



To answer these questions, specific research goals and objectives have been 

 identified tor the six components that comprise the Exobiology Program. 

 Attainment of these goals and objectives will elucidate the evolutionary pathway 

 followed by the major elements that make up living systems — the biogenic 

 elements — leading from their origins in stars, through the formation of the solar 

 system and planets, to the origin and evolution of life on Earth and elsewhere. 

 Accordingly, the broad scientific scope of the program is organized into four 

 evolutionary epochs corresponding to major stages in the evolution of living 

 systems and their chemual precursors: 1) Cosmic Evolution ot the Biogeni* 

 Compounds: i 'he growth in complexity of the biogenic elements from nucleo- 

 synthesis in stars, to interstellar molecules, to organic compounds in asteroids and 

 comets; 2) Prebiotic Evolution: In the context of planetary environments, the 



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