(Submitted April 19, 1998)
Did an asteroid ever hit Earth?
Yes, it is virtually certain that asteroids have hit earth.
First of all, earlier in the history of the solar system there
were probably many more asteroids than there are now, so the
odds of a collision were greater. More recently a large asteroid
impact is credited with having led to the extinction of the
dinosaurs. Other planets and their moons show many craters,
which provide evidence for asteroid impacts. On earth these are
destroyed by weathering. The June 1997 issue of Sky and Telescope has
an article on this subject in which they estimate that a
very large asteroid impact occurs once every 100 million - 1 billion
years (the earth is 4 billion years old), and a large
asteroid impacts once every 1 - 100 million years.
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