Earth once went through a phase known as Snowball Earth, when glaciers spread so far they coated continents closer to the equator.

A closer look

Earth once went through a phase known as Snowball Earth, when glaciers spread so far they coated continents closer to the equator. Imagine nearly the entire planet locked in ice. This happened over 600 million years ago, and remarkably, it may have paved the way for complex life. Extreme cold likely triggered oceans to stockpile nutrients, and when the ice finally melted, conditions were perfect for an explosion of biodiversity. Today, while we face global warming instead of freezing, this history reminds us how fragile and dynamic Earth’s climate system can be. The lesson: our planet has swung between extremes, but current changes are driven by us—and happening much faster.