Researchers from the University of Southampton have presented new data that challenge previous assumptions about Earth's climate during the harshest ice age, known as "Snowball Earth." It was previously believed that during this period, the planet's climate system nearly ceased its activity, with massive ice sheets covering almost the entire surface, reaching as far as the tropics. Exchanges between the atmosphere and oceans were thought to be minimal, and any short-term climate fluctuations were suppressed for millions of years.

New Insights into the "Snowball Earth" Climate

A recent study published in the journal Earth and Planetary Science Letters shows that even at the height of the Sturtian glaciation—the most intense episode of "Snowball Earth," which lasted about 57 million years during the Cryogenian period (720–635 million years ago)—the climate continued to change on yearly, decadal, and centennial scales. These changes resembled modern climate patterns.

The discovery is based on the analysis of exceptionally well-preserved layered rocks—varves—found on the Garvellach Islands off the west coast of Scotland. Each of the 2,600 studied layers in the Port Askaig Formation corresponds to one year of sediment accumulation, allowing scientists to reconstruct ancient climate conditions year by year.

Evidence of Climate Variability

Professor Thomas Gernon, a co-author of the study, notes: “These rocks record the full spectrum of climate rhythms we know today—annual seasons, solar cycles, and interannual variations. All of this occurred even during 'Snowball Earth.' It’s remarkable and suggests that the climate system has an inherent tendency to fluctuate, even under extreme conditions, whenever the slightest opportunity arises.”

Microscopic analysis revealed that the layers formed as a result of seasonal cycles of freezing and thawing in calm, deep waters beneath the ice cover. Statistical analysis of the differences in layer thickness revealed distinct repeating patterns similar to modern climate cycles, such as El Niño and solar cycles.

Short-Term Bursts of Activity

Despite these findings, scientists emphasize that such variability was likely the exception rather than the rule for the entire "Snowball Earth" period. Professor Gernon explains: “The background state of 'Snowball Earth' was extremely cold and stable. What we see here is probably a short-term disruption lasting thousands of years against the backdrop of a deeply frozen planet.”

The Role of Open Water Areas

To understand the causes of these changes, the team conducted climate modeling. The models showed that if the oceans were completely covered by ice, most climate fluctuations would be suppressed. However, if at least 15% of the ocean surface remained ice-free, interactions between the atmosphere and ocean could resume, leading to short-term bursts of climate activity.

Dr. Minmin Fu, who led the modeling, notes: “Our models show that even limited areas of open water in the tropics can allow climate regimes similar to modern ones to operate, creating the very signals we see in the rocks.”

The Importance of Scottish Rocks

The Garvellach Islands have played a key role in reconstructing ancient climate history. Dr. Elias Rugen, who has worked on the islands for the past five years, emphasizes: “These deposits are among the best-preserved 'Snowball Earth' rocks in the world. Through them, we can literally read the climate history of a frozen planet year by year.”

The Significance of the Discovery for Understanding Climate

Understanding Earth's climate behavior during "Snowball Earth" offers insights that go far beyond this ancient era. Professor Gernon concludes: “This work helps us understand just how stable and sensitive the climate system really is. Even in the most extreme conditions Earth has ever experienced, the system could be set in motion. This has profound implications for how planets respond to major upheavals, including our own in the future.”