Marshall Brain's Blog

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According to The Asteroid Tugboat:

On an average night, more than 100 million pieces of interplanetary debris enter Earth's atmosphere. Luckily, most of these bits of asteroids and comets are no bigger than small pebbles; the total weight of the 100 million objects is only a few tons."

Over the course of a billion years, 3 tons of debris a day would add up to a trillion tons. Sand weighs about 100 pounds per cubic foot. A trillion tons of sand would be enough sand to cover an area 3,000 x 3,000 miles with approximately one inch of sand.

Every century, there is a two percent or so chance of a asteroid 100 meters across (or more) hitting earth. So one of these hits earth, with the force of 100 megatons of TNT, approximately once every 40,000 years.

Every century, there is a 0.02 percent or so chance of a asteroid 1,000 meters across (or more) hitting earth. It would hit with the force of 100,000 megatons of TNT, and should happen once every 4,000,000 years or so.