  High-resolution, millimeter observations of disks at the protoplanetary stage
reveal substructures such as gaps, rings, arcs, spirals, and cavities. While
many protoplanetary disks host such substructures, only a few at the younger
protostellar stage have shown similar features. We present a detailed search
for early disk substructures in ALMA 1.3 and 0.87~mm observations of ten
protostellar disks in the Ophiuchus star-forming region. Of this sample, four
disks have identified substructure, two appear to be smooth disks, and four are
considered ambiguous. The structured disks have wide Gaussian-like rings
($\sigma_R/R_{\mathrm{disk}}\sim0.26$) with low contrasts ($C<0.2$) above a
smooth disk profile, in comparison to protoplanetary disks where rings tend to
be narrow and have a wide variety of contrasts
($\sigma_R/R_{\mathrm{disk}}\sim0.08$ and $C$ ranges from $0-1$). The four
protostellar disks with the identified substructures are among the brightest
sources in the Ophiuchus sample, in agreement with trends observed for
protoplanetary disks. These observations indicate that substructures in
protostellar disks may be common in brighter disks. The presence of
substructures at the earliest stages suggests an early start for dust grain
growth and, subsequently, planet formation. The evolution of these protostellar
substructures is hypothesized in two potential pathways: (1) the rings are the
sites of early planet formation, and the later observed protoplanetary disk
ring-gap pairs are secondary features, or (2) the rings evolve over the disk
lifetime to become those observed at the protoplanetary disk stage.
