This work marks a decisive step in the solution of the longstanding problem understanding the origin of the Boson peak in silica glass. The investigation by means of diffuse and inelastic x-ray scattering and lattice dynamics calculations from first principles allow for a direct comparison of the atomic motion in crystalline silica polymorphs and silica glass. The article was selected to illustrate the cover page of Journal of Physics: Condensed Matter, Vol. 27, Nr. 30. The animation shows the intensity distribution of thermal diffuse scattering in 3D reciprocal space.