Scientists find evidence that entirety of Earth was once covered in ice

Even the balmy tropics may have once been crushed by colossal masses of ice.

A severe ice age dominated Earth, some 720 to 635 million years ago, well before dinosaurs stalked the land. But it's uncertain if the entire world froze over during the glaciations of this long-lived, extreme episode, dubbed "Snowball Earth." Now, new evidence from Colorado, an area that once was located in the tropics, suggests mighty glaciers sprawled over even Earth's warmest regions.

"This study presents...