Did you know that portland cement was first made by bricklayer Joseph Aspdin of Leeds, England early in the 19th century by burning powdered limestone and clay in his kitchen stove? It's funny to think that an industry worth 394,553 million USD in 2016 was started by someone messing about in his kitchen. I don't think this bricklayer ever dreamed of the scale and pace at which we use cement today. Massive quantities of limestone, sand, clay, iron ore, bauxite are mined in order to make cement. This industry alone is responsible for 5% of global carbon emissions! (UPDATE: It now accounts for 8% of global carbon emissions). To understand how cement is manufactured today, you can view this quick animation.