We can thank billiard balls for our modern-day, plastic-filled lives. For most of human history, everyday items such as combs were made from expensive animal parts, like tortoise shells. Then, in the 1860s, billiards became a popular pastime. Unfortunately, elephants had to be killed so that their ivory tusks could be made into billiard balls, and soon elephants were rapidly being hunted to extinction. One enterprising New York billiards supplier even offered $10,000 in gold to anyone who could come up with a good substitute for ivory.