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We use accurate estimates of aluminium abundance provided as part of theAPOGEE Data Release 17 and Gaia Early Data Release 3 astrometry to select ahighly pure sample of stars with metallicity $-1.5\lesssim {\rm [Fe/H]}\lesssim0.5$ born in-situ in the Milky Way proper. We show that the low-metallicity([Fe/H]$\lesssim -1.3$) in-situ component that we dub Aurora is kinematicallyhot with an approximately isotropic velocity ellipsoid and a modest netrotation. Aurora stars exhibit large scatter in metallicity and in a number ofelement abundance ratios. The median tangential velocity of the in-situ starsincreases sharply with increasing metallicity between [Fe/H]$=-1.3$ and $-0.9$,the transition that we call the spin-up. The observed and theoreticallyexpected age-metallicity correlations imply that this increase reflects a rapidformation of the Milky Way disk over $\approx 1-2$ Gyrs. The transformation ofthe stellar kinematics as a function of [Fe/H] is accompanied by a qualitativechange in chemical abundances: the scatter drops sharply once the Galaxy buildsup a disk during later epochs corresponding to [Fe/H]$>-0.9$. Results of galaxyformation models presented in this and other recent studies strongly indicatethat the trends observed in the Milky Way reflect generic processes during theearly evolution of progenitors of MW-sized galaxies: a period of chaoticpre-disk evolution, when gas is accreted along cold narrow filaments and whenstars are born in irregular configurations, and subsequent rapid diskformation. The latter signals formation of a stable hot gaseous halo around theMW progenitor, which changes the mode of gas accretion and allows developmentof coherently rotating disk.

From dawn till disk: Milky Way's turbulent youth revealed by the APOGEE+Gaia data