(meteorobs) Larger variety fireball occurrence rates

[Thomas Ashcraft]

"On average, an NEO roughly a half-mile wide or larger hits the Earth 
roughly every 500,000 years, "so we're not expecting one anytime soon," 
Yeomans explained.

"For 500 meters (1,640 feet), we're talking a mean interval of about 
100,000 years," he added. "When you get down to 50 meters, the mean 
interval is about 700 years, and for 30 meters (98 feet), about 140 
years or so, but by then you're getting down to a size where you won't 
expect any ground damage, as they burn up in the atmosphere at about 25 
meters (82 feet) in diameter and smaller, probably for an impressive 
fireball event."

When it comes to truly monstrous NEOs 
<http://www.space.com/scienceastronomy/planetearth/asteroid_jello_001122.html> 
some 10 kilometers (6.2 miles) or larger, of the size thought to have 
helped kill off the dinosaurs, "that's a 100 million year event, and in 
fact, I don't think there is anything like that we see right now," 
Yeomans said."


Above extracted from:

http://www.foxnews.com/story/0,2933,535090,00.html?test=latestnews