The thickness of a galaxy's disk provides a valuable probe of its formationand evolution history. Observations of the Milky Way and local galaxies haverevealed an ubiquitous disk structure with two distinctive components: an oldthick disk and a relatively young thin disk. The formation of this dual-diskstructure and the mechanisms that develop the thickness of the disk are stillunclear. Whether the disk thickness inherit from the birth environment or isestablished through secular dynamical heating after formation is under debate.In this work we identify a relatively young ($\sim$6.6 billion years old)geometric thick disk in the Milky Way, with a scale height of $0.64$ kpc at theSolar Circle. This young thick component exhibits comparable thickness andflaring strength to the canonical old thick disk but is more radially extendedand systematically younger. We also identify thin disk components that formedbefore and after this young thick disk. Detailed analysis of the solar vicinitystructure suggests that the young thick disk marks the onset of a new phase ofupside-down disk formation. These findings strongly discount the role ofsecular dynamical heating and support a turbulent, bursty birth environment asthe primary mechanism behind thick disk formation. The existence of two thickdisk components suggests that the Milky Way has undergone at least two episodesof turbulent and bursty star formation, likely triggered by galaxy mergers.