How many asteroids have hit earth?

People have been worrying about cosmic collisions for a long time, but the field only gained scientific legitimacy in the 1980s when the extinction of the dinosaurs was pinned on a single strike of a comet or asteroid. read more

If a rocky meteoroid larger than 25 meters but smaller than one kilometer ( a little more than 1/2 mile) were to hit Earth, it would likely cause local damage to the impact area. We believe anything larger than one to two kilometers (one kilometer is a little more than one-half mile) could have worldwide effects. read more

A study done in 1996 (looking at the number of meteorites found in deserts over time) calculated that for objects in the 10 gram to 1 kilogram size range, 2900-7300 kilograms per year hit Earth. However, unlike the number above this does not include the small dust particles. read more

2000 -- NASA's Near-Earth Asteroid Tracking System announces new data about large asteroids. "Until now, scientists thought the population of large, near-Earth asteroids was between 1,000 and 2,000, but we've downgraded that number significantly," said David Rabinowitz, now at Yale University. read more

NASA has made efforts to track asteroids, but they haven't been as aggressive as the B612 scientists would like. In 1998, NASA established the Near-Earth Object Program Office to detect potentially hazardous comets and asteroids. read more