Pervasive nanodiamonds indicative of a widespread high temperature impulse lend credence to the hypothethis that a comet breakup over North Americer caused megafauna mass extinctions and brought on the Younger Dyras cold era.

"Something dramatic happened about 12,900 years ago, and the continent of North America was never the same. A thriving culture of Paleo-Americans, known as the Clovis people, vanished seemingly overnight. Gone, too, were most of the largest animals: horses, camels, lions, mammoths, mastodons, saber-toothed cats, ground sloths and giant armadillos.

Scientists have long blamed climate change for the extinctions, for it was 12,900 years ago that the planet's emergence from the Ice Age came to a halt, reverting to glacial conditions for 1,500 years, an epoch known as the Younger Dryas.

The wide distribution of the nanodiamonds could be a sign that the comet broke into pieces in space and that the fragments burned up explosively over a broad area of North America. The heat and pressure from the event transformed carbon on the planet's surface into the tiny diamonds, the scientists said.

"Imagine these fireballs exploding in the air. A Clovis hunter standing and looking at these things would have seen a canopy of fire as these things came in and exploded," said Allen West, a geophysicist and one of the paper's co-authors. "There would have been no sound. There would have been massive explosions. Brilliant light, brighter than the sun. There would have been radiant heat -- it would have been capable, at the very least, of giving him serious burns and, at the maximum, of incinerating him."

Skeptics cite lack of a crater, but tell me where is the Tunguska impact crater?