15,000 to 11,000 years ago Earth experienced a series of climatic fluctuations... there was a short cold spell, known as the Younger Dryas, before the final warming and... end of the last ice age. Based on Greenland ice core data, the Younger Dryas began... 10,900 B.C., and its ending... circa 9700 B.C. and may have occurred within an incredible three years... I once hypothesized that comets were responsible. A comet hitting the land or a shallow ocean, or exploding above the land's surface, scattering dust and debris into the atmosphere, would cause global cooling... This pattern fits well with the...