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Abstract– I summarize recent surveys of protoplanetary disks at millimeter wavelengths and show that the distribution of luminosity, equivalent to the mass in small dust grains, declines rapidly. This contrasts with statistics on the lifetime of disks from infrared observations and the high occurrence of planets from radial velocity and transit surveys. I suggest that these disparate results can be reconciled if most of the dust in a disk is locked up in millimeter and larger-sized particles within about 2 Myr. This statistical result on disk evolution agrees with detailed modeling of a small number of individual disks and with cosmochemical measurements of rapid planetesimal formation.