While just about everyone knows Arizona's Meteor Crater was formed by, well, a meteor impact, what's not widely known is there's been something of a mystery surrounding it. Models of the impact predicted the tremendous pressure and heat should have melted most of the rock, but geologists couldn't find it. Now scientists think they may know why:

A new computer model, reported in the March 10 issue of the journal Nature, shows the incoming object would have slowed considerably during its plunge through the atmosphere, part of it breaking into a pancake-shaped cloud of iron fragments prior to impact.

About half the original 300,000-ton bulk remained intact, smacking the planet at about 26,800 mph (12 km/sec), said the study's lead researcher, Jay Melosh of the University of Arizona.

Which still means you didn't want to be anywhere near that spot when it happened. Since even the most optimistic date for the earliest human migration to the new world is ~ 25,000 years ago, it would seem no one was. Which leads to an amusing spin on an old riddle:

If a meteor smacks the earth hard enough to carve out a crater nearly a mile across and nobody is around to hear it, does it make a noise?

The best answer is, of course, "why does it matter?"