PREBIOTIC PHOSPHORUS CHEMISTRY RECONSIDERED

The available evidence indicates that the origin of life on Earth cert ainly occurred earlier than 3.5 billion years ago and perhaps substant ially earlier. The time available for the chemical evolution which mus t have preceded this event is more difficult to estimate. Both endogen ic and exogenic contributions to chemical evolution have been consider ed; i.e., from chemical reactions in a primitive atmosphere, or by int roduction in the interiors of comets and/or meteorites. It is argued, however, that the phosphorus chemistry of Earth's earliest hydrosphere , whether primarily exogenic or endogenic in origin, was most likely d ominated by compounds less oxidized than phosphoric acid and its ester s. A scenario is presented for the early production of a suite of reac tive phosphonic acid derivatives, the properties of which may have for eshadowed the later appearance of biophosphates.