  The origin of the Earth water reserves during the evolution of the planet is
one of the big miracles in geophysics. Common explanations are storage of water
in the Earth mantle at a time when the crust had not yet formed and depositing
of water by comets during the time of late heavy bombardement. Both
explanations have different problems - especially when comparing with the
evolution of Mars and Venus. Here we discuss the possible role of hydrogen
collected from the solar wind by the early Earth magnetosphere. While the water
production by solar wind capture is very small today it may have been
significant during the first billion years after planetary formation because
solar wind was much stronger at that time and Earth magnetospheric
configuration may have been different. We estimate that the contribution of
solar wind hydrogen to the Earth water reserves can be up to 10% when we assume
a that the Earth dipole acted as a collector and early solar wind was 1000
times stronger than today. We can not even exclude that solar wind hydrogen was
the main contributor to Earth water reserves.
