Earth hasn't always been a hospitable place to live. During several ice ages, the planet's surface was almost completely frozen over, creating what has been dubbed "Snowball Earth."

Liquid water appears to be the most important ingredient for life on any planet, raising the question: how did anything survive such frosty, brutal times?

A group of scientists said Thursday that they had found an astonishing diversity of microorganisms in tiny pools of melted ice in Antarctica, suggesting that life could have ridden out Snowball Earth in similar ponds.