For life to begin, there had to be a source of organic compounds in the prebiotic environment. We now think that some of the compounds were delivered to the Earth on comets, meteorites and dust particles, but others were synthesized in the atmosphere, hydrosphere and in volcanic conditions.

How do we know? This question brings up the important topic of prebiotic simulations. In a simulation, we make a set of assumptions about local conditions on the early Earth, then reproduce those conditions in the laboratory and run experiments to see what happens.

Many people, perhaps most, hate the idea that life might depend on chance processes. It is a human tendency to search for meaning, and what could be more meaningful than the belief that our lives have a greater purpose, that all life in fact is guided by a supreme intelligence which manifests itself even at the level of individual molecules? 

In last week’s column I described how Bill Irvine uses radio astronomy techniques to detect and identify organic compounds in interstellar space. Why is it so important for the origin of life on Earth that organic compounds are scattered throughout our galaxy?

    Last week I described how Fred Hoyle, in 1946,  came up with the idea that carbon is synthesized in hot stars toward the end of their lifetime, and we now know that carbon and the other elements of life are strewn into interstellar space when the star explodes. In his later career, Hoyle was never able to match his earlier triumph of carbon nucleosynthesis, but he certainly tried.

     In the summer of 1981, a colleague at the NASA Ames Research Center in Mountainview, California, gave me a small black stone wrapped in aluminum foil that changed the course of my life.