In 1900, the average U.S. citizen's average life span was 47 years. He traveled about 1,900 km (1,200 miles) in a lifetime and resided in a home with an icebox for food storage and oil or gas for lighting. He communicated by mail, telegraph and crude telephones with limited availability and range. By 2000, the average citizen's life span was 77 years. He traveled an average of 19,000 km/a (12,000 miles/ year) by automobile alone. He resided in a home with many electrical appliances, including refrigerators and electric lights. And the communicated almost instantaneously with any other part of the globe by several widely available means, including portable phones and e-mail. Technology, the application of knowledge about the Earth's materials, their extraction and fabrication into products, helped create this change. Throughout the 20th century, the United States was a leader in technology. Automobiles, refrigerators, electric lighting, telephones and personal computers are only a few examples of the products invented and improved or further developed by American technology (National Academy of Engineering, 2000).