Evidence of Annual Climate Cycles Challenges ‘Snowball Earth’ Narrative
Scientists have uncovered evidence suggesting that Earth’s climate, even during the most extreme ice age known as “Snowball Earth,” wasn’t a static, frozen block. New analysis of ancient rocks from the Garvellach Islands off the west coast of Scotland reveals climate oscillations occurred on annual, decadal and centennial timescales during the Sturtian glaciation, a period lasting approximately 57 million years between and years ago.
The prevailing theory of Snowball Earth posits that during periods of intense glaciation, the planet was almost entirely covered in ice, with little to no liquid water exposed at the surface. This extreme state was thought to have effectively shut down the Earth’s climate system, suppressing short-term variability for millions of years. However, the new research, published in Earth and Planetary Science Letters, challenges this view.
The breakthrough stems from a detailed examination of laminated rocks, known as varves, within the Sturtian Port Askaig Formation. These varves are formed by the annual deposition of sediment, creating a layered record of past environmental conditions. Researchers from the University of Southampton analyzed over 2,600 individual layers, each representing a single year of deposition.
“These rocks preserve the full suite of climate rhythms we know from today — annual seasons, solar cycles, and interannual oscillations — all operating during a Snowball Earth. That’s jaw dropping,” said Professor Thomas Gernon, Professor of Earth and Planetary Science at Southampton and a co-author of the study. “It tells us the climate system has an innate tendency to oscillate, even under extreme conditions, if given the slightest opportunity.”
Decoding Ancient Climate Signals
The microscopic analysis revealed that the layers likely formed through seasonal freeze-thaw cycles in a calm, deep-water environment beneath ice. By statistically analyzing variations in layer thickness, the team discovered repeating climate cycles operating on timescales ranging from a few years to decades. Some of these cycles bear a striking resemblance to modern climate patterns, including oscillations similar to El Niño and solar cycles.
“We found clear evidence for repeating climate cycles operating every few years to decades,” explained Dr. Chloe Griffin, also from the University of Southampton. “Some of these closely resemble modern climate patterns, such as El Niño-like oscillations and solar cycles.”
However, the researchers emphasize that these climate cycles were likely not the norm during Snowball Earth. The study suggests that these oscillations represent short-lived disturbances, lasting thousands of years, against a backdrop of an otherwise deeply frozen planet. “Our results suggest that this kind of climate variability was the exception, rather than the rule,” Professor Gernon clarified. “The background state of Snowball Earth was extremely cold and stable.”
The ‘Slushball Earth’ Hypothesis Gains Traction
To understand how these climate cycles could operate within a Snowball Earth scenario, the team ran climate simulations. The simulations showed that a completely ice-sealed ocean would indeed suppress most climate oscillations. However, if even a small fraction – around 15% – of the ocean surface remained ice-free, familiar atmosphere-ocean interactions could resume.
“Our models showed that you don’t need vast open oceans,” said Dr. Minmin Fu, also from the University of Southampton. “Even limited areas of open water in the tropics can allow climate modes similar to those we see today to operate, producing the kinds of signals recorded in the rocks.”
This finding lends support to the “slushball Earth” hypothesis, which proposes that during Snowball Earth events, the planet wasn’t entirely frozen but instead featured small patches of open ocean, sometimes referred to as “waterbelt” states. These areas of open water would have allowed for some degree of atmospheric and oceanic circulation, enabling the observed climate oscillations.
Implications for Understanding Early Earth and Climate Resilience
The discovery has significant implications for our understanding of Earth’s early climate and the conditions that may have fostered the evolution of complex life. The Snowball Earth episodes occurred before the Cambrian explosion, a period of rapid diversification of life forms. Understanding the climate dynamics during these periods could provide insights into the environmental pressures that drove evolutionary change.
the research highlights the inherent resilience of the climate system. Even under the most extreme conditions, the Earth’s climate appears to have a tendency to oscillate and adapt. This finding could inform our understanding of climate change today and the potential for unexpected feedback loops and resilience mechanisms within the modern climate system.
Dr. Griffin emphasized the unique value of the Scottish rock formations: “These rocks are extraordinary. They act like a natural data logger, recording year-by-year changes in climate during one of the coldest periods in Earth’s history. Until now, we didn’t know whether climate variability at these timescales could exist during Snowball Earth, because no one had found a record like this from within the glaciation itself.”
