Earth absorbs trucks sized asteroids daily. But most of them are too big to get bent out of shape by the Earth's atmosphere.

The smallest asteroid that can harm the planet is about 30 meters [98 feet], but according to a NASA research, these huge asteroids have a chance of hitting the Earth once in every 200 years on an average.

NASA's Near Earth Object (NEO) Program Office makes efforts to identify and track large asteroids in the near-Earth space, including rocks more than a kilometre (0.6 miles) across, which can cause global consequences.

These usually hit the earth in million-year intervals. Larger asteroids, like the ten kilometre one which supposedly killed all dinosaurs 65 million years ago, can plunge the earth into a state of apocalyptic winter for many years. Fortunately though, these impact the earth at an even less frequency of one per tens of millions of years.

The smaller the asteroid, the more they are. Research has discovered 90% of the total over-one kilometre asteroids and none of them pose a threat.

It is simply the increasing knowledge about the position of the asteroids that has reduced the odds of them hitting the earth by 10 fold.