Published online by Cambridge University Press: 12 April 2016
Most records of the first half billion years of the solar system have been wiped out from the planets and from their satellites by their evolution and their morphological differentiation. However, two sources of information seem still to be available on this early period: some meteorites give us clues on the non-volatile fraction that condensed from the primeval nebula, whereas the clues on a more volatile fraction, possibly condensed at a colder temperature, may come from the comets.