1975: The first software to operate a personal computer is developed, but personal computers are not generally available. Scientists in major universities have access to large mainframe computers, but archeologists in the field make notes with pen and paper and have them typed up on electric typewriters.

Today: Many homes in the United States have at least one personal computer, and many people have portable laptop computers. Archeological projects sponsored by universities use computers, global positioning satellite systems, digital cameras, cellular phones, and other electronic equipment.

1975: The United States remains under pressure from the energy crisis of 1973 and continuing fuel shortages. The federal government passes various energy bills to help the country become less dependent on foreign oil and encourages the production of wind farms, solar panels, and dams.

Today: Foreign oil dependency is still a major concern for the United States. Federal policy concentrates...