50. Metal

They constitute the very essence of the modern world; the cadence of our progress sounds in the measured ring of the blacksmith’s hammer. From soaring skyscrapers and sturdy bridges to jet planes and rockets, metals play a key role. Our journey begins before the Bronze Age and takes us into the shiny future when new metal structures–engineered at a molecular level to be stronger, lighter, and cheaper–shape human progress, as they have since man first thrust copper into a fire and forged a tool.