With every passing day, Japan’s chain reaction of disasters pushes the envelope of what humankind regards as unthinkable.

Last week’s 9.0 earthquake was so powerful it literally altered the earth’s rotation and shortened the length of our day. Yet that’s the least of the world-rattling implications from the horrors still unfolding on Japan’s largest island, Honshu.

Foremost on everyone’s mind are the six reactors at the Fukushima Daiichi nuclear complex. Only a few days ago, it was unthinkable that a quake and tsunami would lead to a breakdown of multilayered backup emergency systems there. Then explosions blew the tops off exterior buildings covering the reactors.

And it only got worse. Spent fuel rods in storage ponds overheated as their coolant evaporated. The partial exposure of reactor cores raised the real threat of a meltdown. Radioactivity levels remain at critical levels ― thwarting the best, last-ditch efforts of the Japanese to regain control.

There’s talk of a radioactive plume eventually heading over the Pacific toward California. A southward wind shift could suddenly force yet another unthinkable: the evacuation of Tokyo, a city of 13 million only 140 miles from the Daiichi complex. Already, a mass exodus has begun.

Given the trajectory of this escalating horror, the world is rapidly learning to cast assumptions aside about worst-case scenarios.

Less than a decade ago, who could imagine that the World Trade Center would be leveled by two hijacked jumbo jets, or that, six years ago, an Indian Ocean tsunami would kill 230,000 across Southeast Asia? The past year alone has brought more earthquake devastation to Haiti, Chile and New Zealand, and a man-made disaster sent millions of gallons of crude oil into the Gulf of Mexico.

How many times have you asked yourself in the midst of these events: Can it possibly get worse than this?

“This is uncharted territory,” Secretary of State Hillary Clinton told CNN on Wednesday, suggesting that it’s time to challenge all of our assumptions about the wrath of nature and the dangerous things humans do in the face of it, such as placing nuclear plants near fault lines in a known tsunami corridor.

Gloomy thoughts. But amid all this emerges an inspiring story about the human spirit. With radiation at life-threatening levels, 50 to 100 Japanese nuclear workers have stayed on the job, round the clock, on what seems like a suicide mission to keep the Daiichi reactors from melting down.

Theirs is the ultimate sacrifice to help avert disaster and save lives. It’s the same spirit ― putting service to humankind above personal self-interest ― that Americans celebrated while witnessing the heroism of the 9/11 first responders. Those Japanese workers could easily have given up and gone home to tend to their own families’ urgent post-earthquake needs. And yet, they stayed.

Unthinkable.

(The Dallas Morning News, March 18)