Foreword 



One might think that the origin of life is strictly a biological question, to be 

 attacked by experiments in Earth-based laboratories. That is largely true. But the 

 chemical processes that operated over the eons of remote geological time to 

 produce the first reproducing organisms occurred in the terrestrial environment 

 of that time-and that environment was established by the processes that led to 

 the formation and chemical evolution of the Earth itself. The traces of such 

 processes to be found on the Earth today are studied by Earth scientists, and 

 there is much to be learned of relevance to the origin of life. 



But the Earth did not spring from nothing; it was formed at the same time as 

 the Sun, the planets, and small bodies of the Solar System about 4.5 billion 

 years ago from primitive material in interstellar space. At least the relative 

 abundances of the chemical elements, probably the chemical compounds into 

 which they were combined, and perhaps the detailed physical properties of the 

 pre-Earth material, were established by processes taking place in space before the 

 Earth was formed. At least in principle, then, those who study space have 

 insights to contribute. 



Exobiology, the study of processes relevant to biology that are occurring in 

 space, is becoming a mature field. One immediately thinks of experiments to 

 detect life elsewhere, like the Viking experiments at Mars and searches for radio 

 signals from life elsewhere. Indeed, such studies have been undertaken by 

 NASA's Life Sciences Program. But they are only the most visible elements of a 

 much broader program to uncover phenomena relevant to the origin and evolu- 

 tion of life throughout the universe. Astronomical studies reveal that the abun- 

 dances of the elements in space seem to be very similar throughout our galaxy. 

 Our Sun fits the general pattern because it and the other stars are so massive that 

 as they form, they gravitational ly draw in all types of material without regard to 

 differences in chemical or physical properties. But on-site studies of the planets 

 and satellites of the Solar System-including the Earth-show large variations 

 that can be interpreted in terms of different chemical and physical processes 

 occurring in the solar nebula of gas and dust before the planets formed. The fate 

 of carbon at different places in the solar nebula is an example, and one of great 

 importance for the origin of life. 



In interstellar space, carbon takes a variety of forms. In the dense "molecular 

 clouds" from which stars (and presumably planets) are forming at the present 



