Impact!

An asteroid several miles in diameter slams into Earth along the edge of the present-day Yucatán Peninsula in this artist's impression. The impact, which took place 65 million years ago, gouged a crater almost 200 miles in diameter, killed everything within hundreds of miles, and caused a "nuclear winter" that may have led to the demise of the dinosaurs and most other life on Earth. Such giant impacts are rare, but collisions with smaller space rocks are more common. [Don Davis/NASA]