Throughout much of human history, money took the form of precious metals, coins and even raw materials like livestock or vegetables. The inception of paper money ushered in a bold new era—a world in which currency could purchase goods and services despite having no intrinsic value.While early human societies made extensive use of stone, bronze and iron, it was steel that fueled the Industrial Revolution and built modern cities. Evidence of steel tools dates back 4,000 years, but the alloy was not mass-produced until the invention of the Bessemer Process, a technique for creating steel using molten pig iron, in the 1850s.
