It started without airplanes and ended with spacecraft on Mars and a walk on the moon along the way.

It started without television and ended with wireless Internet surfing and 500 channels, and the invention of the computer along the way.

When it began, life expectancy in America was 47 years; today it's 76.

In a century that has so dramatically redefined how we live, how we think and how we understand ourselves, our universe and time itself, choosing the 10 most important breakthroughs and inventions of the last 100 years is like choosing the most beautiful flower in a garden of roses.

Armed with opinions from college professors and business leaders across the country, we decided to try it anyway.

Picking the most important of anything is inherently tricky. When one invention leads to the next, which is more important, the chicken or the egg?

Some breakthroughs, like Einstein's theory of relativity, redefined our understanding of the universe, while others had far more impact on everyday life.

With those caveats, here's our list, in alphabetical order. Make your own list, and let the arguments begin.

Airplanes: Since Orville and Wilbur Wright took their first powered flight in 1903, airplane travel has made our world smaller. With World War II, airplanes also changed the way wars were fought.

Assembly lines: Though the automobile predates this century, it was Henry Ford's introduction of mass production in 1913 that allowed cars to be purchased by the masses. The car changed how we lived and, with the advent of interstate highways in the 1950s, it offered great freedom of movement. Assembly lines had an incalculable effect on the national economy.

Computers: Since the early mainframes were built in the 1940s, computers have provided a way to solve complex problems and penetrated nearly every aspect of our lives. The rise in the 1990s of the Internet, the World Wide Web and e-mail are redefining how we gather information, how we communicate and, faster than you can say e-commerce, how we shop. The computer's effect on the economy is a revolution unto itself.

DNA model: Francis Crick and James Watson won a Nobel Prize after discovering the twisted-rope-ladder structure of DNA in 1953. Existing in every cell, DNA controls what we look like and our susceptibility and resistance to disease and tells our cells how to act to keep our bodies functioning.

Along with the discovery of DNA itself in the 1940s, these "were absolute foundations for most of what has been discovered concerning biological processes in this century," said Ben Stark, biology professor at the Illinois Institute of Technology.

Today's new gene therapies are at the vanguard of the biggest revolution in medicine since penicillin, the first antibiotic, was developed in 1928. With the advent of cloning, genetics is the basis for one of the most difficult ethical questions facing the 21st century.

Plastics: The first entirely synthetic plastic, Bakelite, was invented - by accident, as it happened - by American chemist Leo Baekeland in 1909. Early uses included radios, light sockets, jewelry, telephones, washing machines, fishing reels and guns.

Later synthetics, like cellophane, nylon and Teflon, brought revolutions of their own.

"Think of how funky the computer would be," said Darren Johnson, computer instructor at Southampton College of Long Island University, "if it were only made of metal and wood."

Refrigeration: First developed in the 1920s, synthetic refrigerants like freon were a huge step forward. They provided for long-term food storage while alleviating the leakage and toxicity of previously used coolants. This not only meant improved food safety and a more constant food supply, but also led to pre-packaged foods and, yes, fast-food restaurants.

The same technology paved the way for air conditioning, leading to the development of Sun Belt cities and improving our comfort and health, thereby extending life expectancy. We also need it to keep computers from overheating.

Space exploration: From the launching of the first satellite in 1957 - Sputnik - to man's walk on the moon 12 years later to today's sophisticated telescopes, shuttles and trips to Mars, space exploration has opened a new frontier. Lessons learned in space also have had implications for some very earthbound problems.

Television: Technology that allowed images to be transmitted over wires was being developed in the 1920s, and the first usable image converter tube was created by Russian-born physicist Vladimir Zworikyn in 1932. That decade saw the first television program services in Germany, Great Britain and the United States.

Ultimately, TV transformed how much and how quickly we see the world, and - more than radio or motion pictures - how we spend our leisure time.

Theory of relativity: Albert Einstein's theories of relativity, spelled out between 1905 and 1915, threw a major curveball into the world's understanding of itself.

For the first time, his work established that space can be curved and that time could differ from point to point. By describing how light moves, he created principles that led us to lasers and transistors. And his suggestion, via his special theory of relativity, that a little mass of matter could create tremendous energy led to the atomic bomb and the nuclear age.

"From the bomb to nuclear power to medical uses, no breakthrough has shown more negative and positive potential," said Joe Luchok of the American Accreditation Healthcare Commission.

The potential of nuclear wars "has framed much of international politics of the last half-century," Stark said.

Transistor: Invented at the AT&T Bell Laboratory in 1947, the transistor "made modern electronics possible," said Harry Shipman, professor of physics and astronomy at the University of Delaware.

Today's computer microchips are essentially tens or even hundreds of millions of transistors and derivative devices on a single wafer of silicon. Without transistors, we wouldn't have personal computers, cell phones, fax machines, modems or most other modern electronic devices.

Daily Herald staff writer Lorilyn Rackl and wire services contributed to this report.

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