Study Suggests

Imagine a time when Earth wasn’t the lush, vibrant planet we know today but a frozen wasteland, entirely encased in ice. For nearly 60 million years, our planet may have been locked in what scientists call a “Snowball Earth” state. Now, researchers have uncovered the best evidence yet for this period of deep freeze, preserved in the rocks of a remote Scottish island chain

The Discovery: Rocks That Tell the Story

Led by scientists from University College London, a research team examined over 2,000 grains of zircon found in the sandstone layers of the Port Askaig and Garbh Eileach formations, part of the Dalradian Supergroup in Scotland and Ireland. Using uranium-lead dating methods, they determined that these rocks were deposited between 720 and 662 million years ago—a time when Earth underwent the Sturtian glaciation, one of two global freezes that may have been responsible for kick-starting multicellular life.

These layers of rock reveal the transition from a warm, tropical Earth teeming with photosynthetic bacteria to an icy wasteland. The gradual shift, preserved in layers untouched by ancient glaciers, provides a rare glimpse into a transformative period in Earth’s history.

Why Is This Important?

The evidence of Snowball Earth has significant implications for understanding how life on Earth evolved. According to the researchers, the Sturtian glaciation likely played a critical role in setting the stage for the emergence of complex, multicellular life forms. As the ice retreated, life that had survived the freeze faced a new, warmer environment, sparking an evolutionary arms race. The ancestors of all animals, including humans, emerged from this frozen epoch.

“This discovery gives us the clearest timeline yet of Earth’s deep freeze,” says Elias Rugen, a PhD candidate in Earth sciences at UCL. “These rocks record a time when Earth was covered in ice, and the retreat of the ice would have been catastrophic for life.”

A Rare Geological Find

What makes this discovery particularly exciting is the preservation of the rocks. In most parts of the world, glaciers scraped away ancient layers, leaving little evidence of the transition. But in Scotland, by some geological miracle, the transition from tropical seas to Snowball Earth is still visible.

“This site could become the official starting point of the Cryogenian Period, marking the beginning of one of Earth’s most extreme climatic events,” explains UCL geochemist Graham Shields.

The research, published in the Journal of the Geological Society of London, provides a groundbreaking look at one of the most important events in Earth’s history—when a frozen Earth began to thaw, giving rise to the rich diversity of life we see today.