  Planetary embryos form protoplanets via mutual collisions, which can lead to
the development of magma oceans. During their solidification, large amounts of
the mantles' volatile contents may be outgassed. The resulting H$_2$O/CO$_2$
dominated steam atmospheres may be lost efficiently via hydrodynamic escape due
to the low gravity and the high stellar EUV luminosities. Protoplanets forming
later from such degassed building blocks could therefore be drier than
previously expected. We model the outgassing and subsequent hydrodynamic escape
of steam atmospheres from such embryos. The efficient outflow of H drags along
heavier species (O, CO$_2$, noble gases). The full range of possible EUV
evolution tracks of a solar-mass star is taken into account to investigate the
escape from Mars-sized embryos at different orbital distances. The envelopes
are typically lost within a few to a few tens of Myr. Furthermore, we study the
influence on protoplanetary evolution, exemplified by Venus. We investigate
different early evolution scenarios and constrain realistic cases by comparing
modeled noble gas isotope ratios with observations. Starting from solar values,
consistent isotope ratios (Ne, Ar) can be found for different solar EUV
histories, as well as assumptions about the initial atmosphere (either pure
steam or a mixture with accreted H). Our results generally favor an early
accretion scenario with a small amount of accreted H and a low-activity Sun,
because in other cases too much CO$_2$ is lost during evolution, which is
inconsistent with Venus' present atmosphere. Important issues are likely the
time at which the initial steam atmosphere is outgassed and/or the amount of
CO$_2$ which may still be delivered at later evolutionary stages. A late
accretion scenario can only reproduce present isotope ratios for a highly
active young Sun, but then very massive steam atmospheres would be required.
