In just a few years, according to this hypothesis, these frigid and sweltering climatic extremes caused the extinction of not just the dinosaurs, but of up to 70 percent of all plants and animals living at the time.

For months, scientists conclude, dense clouds of dust blocked the sun's rays, darkening and chilling Earth to deadly levels for most plants and, in turn, many animals. Then, when the dust finally settled, greenhouse gases created by the impact caused temperatures to skyrocket above pre-impact levels.

According to scientists who maintain that dinosaur extinction came quickly, the impact must have spelled the cataclysmic end.

It is widely agreed that such an object -- 10 kilometers across -- struck just off the coast of the Yucatan peninsula 65 million years ago.

Did a collision with a giant asteroid or comet change the shape of life on Earth forever?