Scientists from University of Southampton have uncovered remarkable new evidence showing that Earth’s climate did not completely shut down during its most extreme ice age, Snowball Earth. This period occurred in the Cryogenian, roughly 720–635 million years ago, when ice sheets stretched to the tropics and the planet may have appeared fully frozen from space. For decades, scientists assumed that such conditions would have largely halted atmosphere–ocean interactions, suppressing short-term climate variability for millions of years.
However, a new study published in Earth and Planetary Science Letters challenges this long-held view. By analyzing exceptionally preserved layered sediments on the Garvellach Islands off Scotland’s west coast, researchers discovered that climate oscillations continued even during this deep freeze. These rocks, deposited during the Sturtian glaciation—the longest and most severe of the Snowball Earth episodes—record annual layers known as varves, allowing scientists to reconstruct climate changes year by year.
The team examined more than 2,600 individual layers from the Port Askaig Formation, with each layer representing a single year of sediment deposition beneath ice. Microscopic analysis suggests these formed through seasonal freeze–thaw processes in calm, deep waters. When researchers applied statistical techniques to variations in layer thickness, they found clear evidence of repeating climate cycles occurring over years to decades. Some of these patterns closely resemble modern climate rhythms, including El Niño–like oscillations and solar-driven cycles.
Lead researchers describe the rocks as a natural “data logger,” capturing seasonal, interannual, and even centennial variability during one of the coldest intervals in Earth’s history. This discovery shows that the climate system retains an intrinsic tendency to oscillate—even under extreme conditions—if given the slightest opportunity. In other words, Snowball Earth was not necessarily a static, lifeless deep freeze at every moment.
Climate simulations helped explain how this could have happened. Models indicate that if the oceans were completely sealed by ice, most climate variability would be suppressed. But if even about 15% of the ocean surface—particularly in tropical regions—remained ice-free, familiar atmosphere–ocean interactions could resume. These small openings would have been enough to generate the kinds of climate signals observed in the Scottish rocks. This supports the idea that Snowball Earth may have been punctuated by short-lived “slushball” or “waterbelt” phases, when limited areas of open water briefly reactivated the climate system.
Importantly, the researchers emphasize that such variability was likely the exception rather than the rule. The background state remained extremely cold and stable, with these oscillations representing temporary disturbances lasting thousands of years against a frozen planetary backdrop.
Beyond illuminating Earth’s deep past, the findings carry broader implications. They reveal how resilient—and sensitive—the climate system can be, showing that even during Snowball Earth, Earth’s climate could be nudged back into motion. This insight helps scientists better understand planetary climate resilience and offers perspective on how Earth, and potentially other worlds, respond to major environmental shocks.
https://phys.org/news/2026-02-snowball-earth-ancient-scottish-reveal.html