Currency.

Overview

Trade is an ancient practice that depended for a very long time on barter. But sometime between 9000 and 6000 BCE, the pluses of a medium of exchange emerged, and cattle became the first form of currency. Better, but still awkward ("Say, do you have change for a Holstein?"). The quest for even greater convenience continued, and between 640 and 630 BCE the Lydians, a people native to Asia Minor, literally coined the first modern form of money by fashioning embossed metal disks from electrum, an alloy of gold and silver.

Paper money (as a circulating medium of exchange) was invented in China between 806 and 812 CE. Unlike precious-metal coins, which have intrinsic value, this important conceptual innovation involved a relatively worthless piece of paper that represented a "promise to pay" backed by stores of valuable metals or other commodities, and led eventually to the invention of modern banking in medieval Italy. Worldwide, 172 different currencies are now in circulation, from the afghani to the zroty. One of the most recent is the euro, introduced in 2002 and used by 300 million people in 12 European Union countries.

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Disposal

Paper and polymer currency also differ when it comes to recycling. Once U.S. dollars have been damaged enough to be taken out of circulation, they are usually shredded at Federal Reserve Banks and pressed into briquettes for landfilling. Some banks find other uses for the over 7,700 tons of currency taken out of circulation every year; some sell the notes to private businesses, such as companies that produce stationery from the shreds.

Worn-out polymer currency is also shredded, but it is then melted down and formed into pellets for recycling. The polymer pellets can be refashioned into a variety of products, from compost bins and plumbing supplies to wheelbarrows and roof shingles. Since polymer notes last roughly four times as long as paper notes, fewer notes need to be produced, saving resources and minimizing waste.

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Manufacture and Use

Depending on the country, governments either produce currency themselves or contract it out to private companies. In the United States, the Bureau of Engraving and Printing prints about 35 million notes daily, using a 75-percent-cot-ton, 25-percent-linen paper in which red and blue fibers are embedded to prevent counterfeiting. Newer U.S. dollars have additional anti-forgery features, such as color-shifting ink, high-tech watermarks, and a security thread. Of the dollar notes printed each year, 95 percent replace those in circulation. On average, a dollar bill lasts up to 22 months, the $10 bill lasts 18 months, and the $100 bill has a lifetime of 60 months.

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Most currencies are made from paper, but plastic money is gaining in popularity. Pioneered by Australia in 1988, plastic polymer notes have been put into circulation in 22 countries, including Bangladesh, Kuwait, Mexico, Romania, and Zambia. The clear laminated polymer film is coated with layers of special inks, raised print, and protective varnish. Although originally designed to reduce forgery with security devices that cannot be used with paper notes, polymer notes have other advantages. They are durable and more hygienic than paper bills, which easily absorb sweat, dirt, and germs; dollar bills have even been found to carry traces of pathogenic bacteria, marijuana, and cocaine.

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