The vertical profiles of chain and spiral galaxies in the Hubble Space Telescope Ultra Deep Field ( UDF ) are fit to sech ^ { 2 } \left ( z / z _ { 0 } \right ) functions convolved with stellar profiles in order to measure the disk scale heights z _ { 0 } in four passbands . The bulge regions of the spirals are avoided . Photometric redshifts give absolute scales . The rms heights of the giant clumps in these galaxies are also measured . The results indicate that UDF disks are thick with an average z _ { 0 } = 1.0 \pm 0.4 kpc . The ratio of radial exponential scale length to z _ { 0 } is \sim 3 \pm 1.5 . The scale heights are only 20 % larger than the radii of the giant star-forming clumps and a factor of \sim 10 larger than the rms clump deviations around the midplanes . This suggests the clumps formed from midplane gas and dissolved to make the thick disks . Redshifted stellar population models suggest ages of \sim 1 Gy and mass column densities from 4 to 40 M _ { \odot } pc ^ { -2 } . The UDF disks look like young versions of modern thick disks . This resemblance is difficult to understand if galaxies grow over time or if subsequent accretion of thin disks gravitationally shrinks the observed thick disks . More likely , high redshift disks are thick because their mass column densities are low ; a velocity dispersion of only 14 km s ^ { -1 } reproduces the observed thickness . Modern thick disks require more heating at high redshift . This is possible if the gas that eventually makes the thin disk is in place before the youngest age of a modern thick disk , and if the existing stars are heated during the delivery of this gas .