Earth has been visited by meteorites many times. More than 140 meteorite craters demonstrate that. These scars are usually thousands or millions of years old. The most famous one is the Barringer crater in Arizona (age 40,000, size 1200 meters, depth 180 meters). South Africa owns the oldest dated meteorite hole on Earth. The Vredefort crater spans 140 kilometres and is almost 2,000,000,000 years old.
Regarding the earth's age, the number of craters seems quite low. But many impacts have already faded away or are invisibly hidden on the bottom of the ocean. Extra-large bangs are really exclusive however. The most striking that we know of is that of 65 million years ago, when the dinosaurs became extinct. A 10 kilometres wide planetoid crashed onto earth, causing a collision comparable to an explosion of hundreds of nuclear bombs. Off the Yucatan coast (Mexico) a 180-km crater was formed. Dust and vapour formed a veil around the Earth, blocking out the sunlight. Most plants and animals died. No more than twenty percent of all life forms on Earth survived, including some small mammals, among which the predecessors of the human race.
These disastrous impacts are very rare. Scientists have calculated that rocks of this size collide with earth once every 100 million to 1 billion years. The smaller ones however seem to visit our region more often. For example on December 9, 1994: a meteoroid with the size of a house neared our planet at 100,000 kilometres. This seems a lot, but astronomically speaking you could feel the wind while it was passing. On crashing with earth, this rock would have caused an impact almost similar to the Hiroshima bomb.
On October 26, 2028, the near-Earth asteroid 1997 XF11 will make a close approach to our planet. Initial reports indicated an extremely close passage. At that time the error margin was still so large that an impact could be possible. The current analyses predict an approach distance of 0.00636 AU (951,000 km) or about 2.5 times farther than the moon. The probability that the asteroid will impact the Earth is effectively zero.