Molecular clouds protoplanetary disk formation

The collapse of rotating molecular cloud cores leads to the formation of massive accretion disks that evolve to more tenuous protoplanetary disks. Disk evolution is driven by a combination of viscous evolution, grain coagulation, photoevaporation, and accretion to the star. The pace of disk evolution can vary substantially, but massive accretion disks are thought to be typical for stars with ages < 1 Myr and lower-mass protoplanetary disks with reduced or no accretion rates are usually 1-8 Myr old. Disks older than 10 Myr are almost exclusively non-accreting debris disks (see Figs. 1.3 and 1.5). 

---