Many of the era's incorrect predictions centered on resource scarcity--oil, minerals, food--but perhaps the most famous one came ten years after the first Earth Day, when a scientist and economist made a public bet that lives on in environmental discourse today.

The scientist was Paul Ehrlich, an outspoken biologist whose studies on the population dynamics of butterflies led him to a dramatic conclusion: That the human population was too big and soon would strip the world of resources, leading to mass starvation.

The economist was Julian Simon, who disagreed with Ehrlich. Humans are not butterflies, he argued, and have a powerful tool that prevents resource scarcity: a market economy. When a useful resource becomes rare, it becomes expensive, and that high price incentivizes exploration (to find more of that resource) or innovation (to create an alternative).

The two never met or debated in person. But in 1980, Simon challenged Ehrlich to a bet in the pages of a scientific journal, and Ehrlich accepted. The biologist selected five raw minerals--chromium, copper, nickel, tin, and tungsten--and noted how much of each he could buy for $200. If his prediction was right and resources were growing scarce, in 10 years the minerals should become more expensive; if Simon was correct, they should cost less. The loser would pay the difference.

In October 1990, ten years later, Simon received a check in the mail from Ehrlich for $576.07. Each of the five minerals had declined in price. Simon and his faith in the market were victorious.

"The market is ideally suited to address issues of scarcity," says Paul Sabin, a Yale environmental historian who wrote the book on the Simon-Ehrlich Wager.