Cosmic Dust Supports a Snowball Earth.

This article presents views of paleoclimatologists about Earth's climate. Indeed, the revival of the Snowball Earth hypothesis almost 7 years ago has bogged down of late, as paleoclimatologists have failed to turn up unequivocal evidence that ice enrobed the planet. A group of geochemists offers a new snowball marker: the element iridium, which continually rains down on us from space. They say they found so much iridium deposited at the end of a glaciation 635 million years ago that the planet must have been frozen pretty much solid for 12 million years straight.