Since 2007, most of humanity has lived in cities made possible by concrete. Of course, there are plenty of other materials in urban buildings: skyscrapers have steel skeletons covered by glass or metal; detached houses in North American suburbs are made of wood (studs, plywood, particle board) and gypsum drywall (and are often sheathed in brick or stone); and engineered lumber is now used to build apartments many stories high.[82]
