Exploding rocks and flaming ice

Though some historians believe that thousands of Chinese people were killed in 1490 by a hail of "falling stones", most experts are of the opinion that nobody has ever been killed by asteroid or comet attack from space. (The death-dealing "hailstones from heaven" of Joshua 10:11 were a miraculous and unique phenomenon.) Should the unthinkable happen, and your town or region were to suffer annihilation by a huge boulder from space, you'll know nothing of it. So why worry? By contrast, the spiritually blindest and deafest of souls ought to be goaded into at least grudging admiration for the genius of the One who created the laws of high-energy ballistics and deigned to give us some close-up views of their power at work. As the latest issue of National Geographic describes in "Target Earth", insignificant specks from space can makes jaws drop and eyes pop from their sockets when they drop by. When, in 1908, one of the estimated ten million asteroids or comets crossed our path and was seduced by our gravitational field, the results were pretty spectacular for people living in the region of Tunguska, Russia. As usually happens, the building-sized object exploded and vaporized a few miles above the ground creating an immense fireball of bluish light almost as bright as the sun and scorching and knocking down an estimated 80 million trees across 800 square miles. An accompanying shockwave knocked many people off their feet and shattered windows hundreds of miles away. For days afterwards, "people in Europe could read outdoors at night" (National Geographic). For more, see "Select Eyewitness Reports" in the Wikipedia article "Tunguska Event".

Even though the smallest metallic meteorites hit the atmosphere at a speed no lower than seven miles (11 kilometers) per second, the drag of the atmosphere slows them down sufficiently to produce little or no effect at ground level. Larger rocky asteroids up to about ten meters across stray into our space about once per year but even they vaporize in the upper atmosphere, causing no damage and rarely being seen. The Tunguska object was large by comparison with any of these - and objects its size are estimated to pay us a call about once every thousand years - yet it was a pipsqueak compared with some of our past visitors. Much larger asteroids and comets have struck us in the past with, in some cases, withering effects. The

largest in "recent" times, estimated at six miles across, was the notorious Chicxulub impactor that barreled into the Gulf of Mexico 65 million years ago releasing thousands times more energy than all the world's nuclear weapons combined and wiping out the dinosaurs in the process. Such large species create craters when they land on terra firma, the most famous crater in America being Meteor Crater (aka Barringer Crater) in Arizona. Older craters can be almost impossible to recognize from the ground, particularly if they have been subject to eons of erosion. Just this year scientists announced that an impactor about 1650 feet (50 meters) wide smashed into Scotland near the city of Ullapool about 1.2 billion years ago, gouging out a crater about 6 miles (10 kms) in diameter. Over time sandstone debris covered the crater, rendering it unrecognizable as such. Those that land in water can be even harder to detect. If only James Michener had known about the 53-mile-wide crater buried under Chesapeake Bay when he wrote his blockbuster novel "Chesapeake"!

The physics of large impacts fascinates those who study them. After all, how strange to contemplate that huge chunks of frozen gases near absolute zero - the stuff of comets - can create massive fireballs. But as everybody who has studied high school physics knows, energy cannot be created or destroyed but it can be transformed into different forms. The kinetic energy of a frozen chunk of ice traveling at seven miles or more per second is enormous. When such an object hits our atmosphere, divinely-ordained laws of physics come into play and work their miraculous transforming alchemy, turning rushing chunks of bitter coldness into raging infernos. Unbelievable.

With all the negative press given to impactors because of their potential for destruction, the truth is that they have served as marvelous tools in God's hands in making our planet the wondrous place it is, extinctions notwithstanding. For the first day or two of creation, impacts were commonplace, kneading earth's surface as a baker kneads his dough. In those days, impacts were a billion times more common than today, their numbers decreasing progressively with the passage of time. How amazing that evolution got its timing just right for the appearance of man.