When an Asteroid Hits -- a Killer Crash

An asteroid colliding with Earth: It's the largest global disaster that has ever happened, and scientists say with 100 percent certainty that it will happen again. The question is not if but when.

Scientists have located more than 100,000 asteroids. Some are tiny, others as large as the state of Texas, and sooner or later, a huge one will crash with Earth.

Astronomers already have their eyes fixed on an asteroid called Apophis, which is scheduled for a close encounter with Earth in 2029.

Scientists have calculated that, on April 13, 2029, Apophis will pass so close to Earth it will actually fly underneath our communication satellites. Depending on the path of the asteroid, scientists say there is a small chance Apophis could collide with Earth on its return orbit in 2036.

If a large enough asteroid did collide with Earth, we would first feel a huge shock wave caused by the asteroid hitting the atmosphere. As the asteroid hurtles through the atmosphere even before impact, the ground in an area hundreds of miles around would be flattened. Seconds later, the asteroid would strike the ground and explode into a fiery ball, packing more energy than the entire nuclear arsenal of all the world's countries.

The last time one of these "civilization busters" hit the planet was 65 million years ago, and it helped wipe out an entire species of dinosaurs. Could the dinosaurs' fate ultimately be ours?