1. First beginnings
Many scientists believe that a variety of organic compounds, such as formaldehyde, hydrogen cyanide and even some amino acids, were readily available on the early Earth to take part in the kinds of prebiotic chemical reactions that may have led to the development of life. These compounds would have come from two main sources.
They could have been produced by the photodissociation and polymerisation of atmospheric molecules, such as carbon dioxide, methane and ammonia, through a combination of high temperature, ultraviolet light and bolts of lightning. The feasibility of this process was first shown in experiments performed by Harold Urey and Stanley Miller at the University of Chicago, US, in 1953.
In addition, they may have been delivered to the early Earth within the bodies of comets and meteorites. Organic compounds have been found in meteorites that have landed on Earth and have also been detected in comets using infrared telescopes. Laboratory simulations of the interstellar environment have shown that UV light could power the formation of these organic compounds in dense molecular clouds (see Chem. Br., January 1999, p 28).
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