  In the current cosmological model, only the three lightest elements were
created in the first few minutes after the Big Bang; all other elements were
produced later in stars. To date, however, heavy elements have been observed in
all astrophysical environments. We report the detection of two gas clouds with
no discernible elements heavier than hydrogen. These systems exhibit the lowest
heavy-element abundance in the early universe and thus are potential fuel for
the most metal poor halo stars. The detection of deuterium in one system at the
level predicted by primordial nucleosynthesis provides a direct confirmation of
the standard cosmological model. The composition of these clouds further
implies that the transport of heavy elements from galaxies to their
surroundings is highly inhomogeneous.
