Beware the Stones from Heaven

by Michael Hofferber. Copyright © 1998. All rights reserved.

The moon is full and rising over the plain, saturating our town's quiet streets with its milky glow. I can feel its light against my skin. It casts shadows behind me.

Against the hush of this lunar glare a red fireball arches across heaven. The gaseous atmosphere makes it burn, whirling and sparking and breaking apart on its way to earth. In the stillness I think I hear it crackle and pop. Then it's gone.

Twenty years ago a group of scientists -- Luis Alvarez, Walter Alvarez, Frank Asaro, and Helen Michel -- suggested that a giant meteorite slammed into Earth 65 million years ago, causing the extinction of the dinosaurs and other species.

The murderer's fingerprint, they claimed, had been left behind in the Earth's geologic record. A metallic element called iridium is rare on Earth but common in meteorites. Dig deep enough and in the right places and you'll find significant amounts of iridium deposited in 65-million-year-old layers of rock all over the planet.

Before the iridium shows up in the geologic record, dinosaurs populated the Earth. After the iridium layer, the dinosaurs are gone.

The Alvarezs' claim shook up the scientific community. Trained to see gradual geologic and biological changes occurring across eons of time, few scientists could accept the idea of a "global catastrophe" disfiguring the planet and causing mass extinctions. Many still don't.

But the evidence is all about. The moon above beams down its own witnesses. The basalt-filled mares, dark areas staring down from its full face, are craters of ancient meteorite collisions.

Earth has been pocked too, many times. More than 3,000 meteorites hit the ground, or the ocean, every year. Most are small, insignificant. But on occasion, perhaps once in a hundred million years, something bigger comes flying through space.

In 1993, a huge comet called Shoemaker-Levy 9 nearly collided with Jupiter. As it passed through the planet's gravitational field it broke apart into more than a dozen pieces before continuing on its way. Astronomers who discovered it then said it looked "like pearls on a string."

Later, on its return trip through the solar system, those pearls collided one after another with Jupiter, creating a grand spectacle witnessed by people at telescopes all over the Earth.
This year, two major motion pictures have examined the consequences of a similar collision with our planet. Could the asteroids hurling toward us be diverted? Could we survive the impact? Would it spell the end of life on Earth?

It wasn't that long ago that our forefathers were certain that the Earth was a stable place and unmoving, and that we were situated at the center of the universe. The sun existed to give light to our daily affairs and each star, in European folklore, was illuminated to represent a living person and would go out when that person died.

Some folks were born under "a lucky star" and others were suffered to live unlucky. When a meteor went streaking across the night sky, we made wishes on it, quickly, before its light was consumed.

Today we live with the knowledge that the Earth beneath our feet is but one planet among many, twisting and turning and racing through space at incredible speed. Our planet revolves around the center of a galaxy that is being propelled away from some central location like debris from a great explosion.

And those falling stars we have been wishing upon are actually huge chunks of rock and ice being thrown our way from the depths of space.

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