In 1906, we had the earthquake.

Trouble at Three Mile Island set off a nuclear power panic in 1979.

And the 1986 Challenger explosion left the future of America's space program in doubt.

Looking back on 20th century disasters, it's easy to focus on the devastation and mayhem left behind.

Yet many of the important inventions, regulations and safety standards we have today might never have existed were it not for a major disaster.

Examples abound: No one would deny that Marie Curie's 1934 death from leukemia or anemia was a tragic consequence of all her years of exposure to radium. Yet the work that killed her led to the discovery of life-saving cancer treatments and sophisticated medical diagnostic equipment, nuclear energy and the atomic bomb.

The same could be said of the sacrifices made by countless others involved in disasters that, ultimately, led to progress.

After the earthquake The California earthquake of April 18, 1906, shook the earth from southern Oregon to south of Los Angeles and inland as far as central Nevada. The quake sparked fires throughout San Francisco and left at least 700 dead, though experts now say the death toll might have been three or four times that amount.

At the time, the earthquake was notable for its size and destruction. Today, however, the 1906 quake is remembered more for its contributions to science and engineering.

The disaster marked the first time scientists closely studied an earthquake's aftermath, contributing much of what we know today about what causes an earthquake, said Paul Reasenberg, a geophysicist with the U.S. Geological Survey.

Those early studies laid the groundwork for testing later in the century that ultimately determined what kind of shaking can be expected from an earthquake and how much a structure can withstand. Using that information, engineers developed quake-resistant buildings and governments toughened construction codes.

"Fewer people are going to die because of these changes," Reasenberg said.

NASA comeback When the space shuttle Challenger exploded on Jan. 28, 1986, killing all seven crew members on board, many wondered whether it would be the end of America's space program. The disaster did indeed ground the shuttle program for two years, but by 1988, an improved shuttle launched a new era of safety for NASA.

The Discovery boasted more than 100 mandatory modifications. But NASA didn't stop there. Since 1992, improvements to the shuttle main engines have more than quadrupled estimates of their safety and improvements throughout the shuttle's systems have more than tripled estimates of the overall safety of the shuttle.

Three Mile Island legacy On March 28, 1979, the Three Mile Island power plant near Middletown, Penn. became the site of the most serious U.S. commercial nuclear power plant in operating history.

Even though the accident resulted in no deaths or injuries to plant workers, it was serious enough to bring about sweeping changes involving emergency response planning, reactor operator training, human factors engineering, radiation protection and many other areas of nuclear power plant operations.

The catastrophe also caused the U.S. Nuclear Regulatory Commission to tighten and heighten its regulatory oversight. All of this has added up to a safer nuclear power industry, according to the NRC.

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