  Although thick disk is a structure prevalent in local disk galaxies and also
present in our home Galaxy, its formation and evolution is still unclear.
Whether the thick disk is born thick and/or gradually heated to be thick after
formation is under debate. To disentangle these two scenarios, one effective
approach is to inspect the thickness of young disk galaxies in the high
redshift Universe. In this work we study the vertical structure of 191 edge-on
galaxies spanning redshift from 0.2 to 5 using JWST NIRCAM imaging
observations. For each galaxy, we retrieve the vertical surface brightness
profile at 1 ${R_e}$ and fit a sech$^2$ function that has been convolved with
the line spread function. The obtained scale height of galaxies at $z>1.5$ show
no clear dependence on redshift, with a median value in remarkable agreement
with that of the Milky Way's thick disk. This suggests that local thick disks
are already thick when they were formed in the early times and secular heating
is unlikely the main driver of thick disk formation. For galaxies at $z<1.5$,
however, the disk scale height decreases systematically towards lower redshift,
with low-redshift galaxies having comparable scale height with that of the
Milky Way's thin disk. This cosmic evolution of disk thickness favors an
upside-down formation scenario of galaxy disks.
