Telltale Craters, Explosions, and Collisions

It is not difficult to believe that our planet has been hit by large objects raining down from space in the past. Proof of these impacts can be found in the more than 150 discovered craters that pockmark earth’s surface. Some of them are clearly visible, others can be seen only from aircraft or satellites, and still others have long been buried or are on the ocean floor.

One of the most famous of these craters, known as Chicxulub, produced a scar on earth’s surface 110 miles [180 km] in diameter. Located near the northern tip of Mexico’s Yucatán Peninsula, this huge crater is believed to be the impact site of a six-mile [10 km]-wide comet or asteroid. Some claim that the climate changes triggered by this impact caused the extinction of the dinosaurs and of other land and sea animals.

In Arizona, U.S.A., an iron meteorite gouged out the spectacular Meteor Crater—a hole nearly 4,000 feet [1,200 m] across and 600 feet [200 m] deep. What would the casualties be if a meteorite like that hit a city? A popular display at the American Museum of Natural History, in New York City, shows that if such an object were to hit Manhattan, that crowded borough would be completely destroyed.

On June 30, 1908, an asteroid or a chunk of a comet estimated to be less than 300 feet [100 m] across roared into the atmosphere and exploded some five miles [10 km] above the largely unpopulated Tunguska region of Siberia, as mentioned in the introduction. The blast, estimated at 15 megatons, devastated an area of 800 square miles [2,000 sq km], knocking down trees, starting fires, and killing reindeer. How many people would have died if ground zero of that explosion had been a densely populated area?

Disaster Scenarios

With trepidation, scientists have considered the dire consequences that a comet or asteroid impact would have on our planet. This is how they envision the immediate results of a major collision. First would come an explosive plume of rock and dust. The falling debris would produce a meteor shower that would turn the sky red-hot and ignite forests and grasslands, killing most land life. Dust remaining suspended in the atmosphere for a longer period would block sunlight, causing temperatures to plummet and halting photosynthesis on the darkened surface below. Suppression of photosynthesis would also lead to a breakdown in the oceanic food chain, condemning to death most marine creatures. According to this scenario, the environmental disaster would be rounded out by global acid rain and the destruction of the ozone layer.

Were such an asteroid to hit the ocean, it would produce tidal waves, tsunamis, with tremendous potential for destruction. Tsunamis would travel much farther from the impact site than the initial shock wave and would produce widespread destruction in coastal areas thousands of miles away. Says astronomer Jack Hills: “Where cities stood, there would be only mud flats.”

However, one must be careful about such assertions. Much of this theorizing is mere speculation. Obviously, nobody has seen or studied an asteroid colliding with the earth. Also, today’s hype-crazy media are quick to come up with sensational headlines, based on incomplete or even inaccurate information. (See the box above.) Actually, it is said that the chance of being killed by an object falling from the sky is significantly less than the chance of being killed in a car accident.