Around 700 million years ago, the Earth cooled so much that scientists believe massive ice sheets encased the entire planet like a giant snowball. This global deep freeze, known as Snowball Earth, endured for tens of millions of years.

Geologists found evidence in the way enigmatic sandstones called Tava formed in the Rocky Mountains hundreds of millions of years ago.

Ever since the term “Snowball Earth” was first proposed in a 1992 paper, it has prompted substantial debate among scientists.