  Discs of gas and dust are ubiquitous around protostars. Hypothetical disc
viscosity is thought to cause the gas and dust to accrete onto the star.
Turbulence within the disc might be the source of this disc viscosity. However,
observed protostellar disc turbulence often appears to be small and not always
conducive to disc accretion. In addition, theories for disc and planet
evolution have difficulty in explaining the observed disc rings/gaps which form
much earlier than expected.
  Protostellar accretion discs are observed to contain significant quantities
of dust and pebbles. Observations show that some of this material is ejected
from near the protostar, where it travels to the outer regions of the disc.
Such solid infalling material has a relatively small amount of angular momentum
compared to the material in the disc. This infalling material lowers the
angular momentum of the disc and should drive a radial flow towards the
protostar.
  We show that the local radial speed of the disc is proportional to the mass
rate of infalling material onto the disc. Higher rates of infall onto the disc
implies higher radial accretion disc speeds. As such, regions with high rates
of infall will produce gaps on relatively short timescales in the disc, while
regions associated with relative low rates of infalling material will produce
disc rings. As such, the inner edge of a disc gap will tend to have a higher
surface density, which may enhance the probability of planet formation. In
addition, the outer edge of a disc gap will act as a dust trap and may become a
site for planet formation.
  For the early Solar System, such a process may have collected O$^{16}$-poor
forsterite dust from the inner regions of the protosolar disc and O$^{16}$-rich
CAIs and AOAs from the inner edge regions of the protosolar disc, thereby
constructing a region favourable to the formation of prechondritic
planetesimals.
