We live in a shooting gallery, here in the inner solar system. If it were not for the erosion effects of the atmosphere and plant life, earth's surface would look like the Moon's. But if you know where to look, lots of crater remnants can be found on earth.
The late Eugene Shoemaker, of the U.S. Geological Survey, said that a meteorite that produces an explosion at least equivalent to the Hiroshima nuclear blast impacts earth at least once a year. These are not widely noticed because most of the earth's surface is open ocean, most of the land is uninhabited wilderness, and for some reason many of the meteorites explode in the upper atmosphere, producing little effect that reaches the earth's surface other than sometimes a thundering roar and flash of light. He may in fact have underestimated the frequency of these meteorite "hits."
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