Longest Ice Age

Geological evidence suggests that the Earth endured several severe ice ages early in its history. The longest and most severe was between 2.3 and 2.4 billion years ago, and lasted around 70 million years. During this period, the entire Earth was probably covered in ice, possibly to a depth of 1 km (0.6 mile). In March 2007 research was published which suggests that Snowball Earth actually experienced periods of warmth, casting doubt on whether or not the ice coverage ever actually reached 100%.