posted on Apr, 19 2014 @ 08:07 PM
a reply to: FlyersFan
Yes we've been lucky, but the luck isn't completely blind.
The Tunguska impact in 1908 would have devastated a city but it instead leveled the forest in a remote area. In fact amazingly we don't know of even a
single death from it.
It helps that most of the Earth is covered by water and not land, and also that large areas of land are uninhabited.
I'm not sure what percentage of the land mass is occupied by cities, but let's say 4% (anyone has a better guess or figure let me know). Factor in the
percentage of ocean and this leaves roughly a 1% chance that a city killer like the Tunguska impactor would actually impact a city.
It was thought that the Tunguska type impact happened say every 500 years or so. I'm not completely convinced the data in the article shows that it
happens 10x more often, but assume this is true and they happen every 50 years. Once you factor in the 1%, this means a city would be leveled once
every 5000 years.
In any case, the fact that Earth is at risk from city killers shouldn't be surprising to anybody who has followed NASA's press releases about their
search for Earth crossing orbits which states they don't know the orbits for most objects below a certain size, which happens to include city
To the people who said there's nothing we can do, it depends on how much warning we get but if it's sufficient we could at least evacuate the city,
which wouldn't save the buildings but could at least save the people.
edit on 19-4-2014 by Arbitrageur because: clarification