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.