Crust Posted on 6th November 201520th April 2022 by ThePD (The Project Definition) Crust is 1) the solid, outermost layer of the Earth that is typically 5 km to 75 km thick; 2) a hard outer covering on a loaf of bread or a pastry. Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window)Click to share on LinkedIn (Opens in new window) Related Posted in Science and tagged geology. ThePD (The Project Definition) ThePD has been developing the Preferred Project Definitions based on the actual project execution and operation experiences and knowledge with the Project Language, and sharing with you daily basis.