How common are meteorite strikes?

A meteor exploded in the sky above Russiaon Friday, causing a shockwave that blew out windows injuring hundreds of people and sending fragments falling to the ground in the Ural Mountains. Here's a look at those objects in the sky:

What's the difference between a meteor and a meteorite?

Meteors are pieces of space rock, usually from larger comets or asteroids, which enter the Earth's atmosphere. Many are burned up by the heat of the atmosphere, but those that survive and strike the Earth are called meteorites. They often hit the ground at tremendous speedup to 30,000 kilometers an hour, according to the European Space Agency. That releases a huge amount of force.

How common are meteorite strikes?

Experts say smaller strikes happen five to 10 times a year. Large impacts such as the one Friday in Russia are rarer but still occur about every five years, according to Addi Bischoff, a mineralogist at the University of Muenster in Germany. Most of these strikes happen in uninhabited areas where they don't cause injuries to humans.

What caused the damage in Russia?

Alan Harris, a senior scientist at the German Aerospace Center in Berlin, said most of the damage would have been caused by the explosion of the meteor as it broke up in the atmosphere. The explosion caused a shockwave that sent windows and loose objects flying through the air in a radius of several kilometers. By the time the remaining fragments hit the ground they would have been too small to cause significant damage far from the site of impact, he said.

Is there any link to the asteroid fly-by taking place later Friday?

No, it's just cosmic coincidence, according to European Space Agency spokesman Bernhard Von Weyhe, who says Asteroid 2012DA14 is unrelated to the meteorite strike in Russia.

When was the last comparable meteorite strike?

In 2008, astronomers spotted a meteor heading toward Earth about 20 hours before it entered the atmosphere. It exploded over the vast African nation of Sudan, causing no known injuries. The largest known meteorite strike in recent times was the "Tunguska event" that hit Russia in 1908. Even that strike, which was far bigger than the one that happened over Russia on Friday, didn't injure anyone. Scientists believe that an even larger meteorite strike may have been responsible for the extinction of the dinosaurs about 66 million years ago. According to that theory, the impact would have thrown up vast amounts of dust that blanketed the sky for decades and altered the climate on Earth.

What can scientists learn from Friday's strike?

Bischoff says scientists and treasure hunters are probably already racing to find pieces of the meteorite. Some meteorites can be very valuable, selling for up to (euro) 500 ($670) per gram depending on their exact composition. Because meteors have remained largely unchanged for billions of years -- unlike rocks on Earth that have been affected by erosion and volcanic outbreaks -- scientists will study the fragments to learn more about the origins of matter. Harris, of the German Aerospace Center, says some meteorites are also believed to carry organic material and may have influenced the development of life on Earth.

What would happen if a meteorite hit a major city?

Scientists hope never to find out, but they're still trying to prepare for such an event. Von Weyhe, the European Space Agency spokesman, says experts from Europe, the United States and Russia are already discussing how to spot potential threats sooner and avert them. But don't expect a Hollywood style mission to fly a nuclear bomb into space and blow up the asteroid.

"It's a global challenge and we need to find a solution together," he said. "But one thing's for sure, the Bruce Willis Armageddon method won't work."