Under the Song dynasty, in the early 11th century, merchants in Sichuan issued paper receipts so people wouldn't have to lug around heavy iron coins; the state took over issuing them around 1024. Marco Polo later marvelled at these notes. Europe's first banknotes didn't appear until 1661, in Sweden, and China learned early on how printing too much money fuels inflation.
That's the estimate from a WHO-led study published in The Lancet in 2024, covering the half-century since the Expanded Programme on Immunization was launched in 1974. It works out to about six lives saved every minute, mostly infants. The measles vaccine alone accounts for around 60% of those lives.
According to the World Gold Council, about 216,000 tonnes of gold have been mined in all of human history. Because gold is so dense (19.3 tonnes per cubic metre), it would fit in a cube about 22 metres on each side, roughly the height of a seven-storey building. Strikingly, about two-thirds of it has been mined since 1950.