New findings suggest that an ice-covered world can still undergo seasonal changes, climatic fluctuations, and solar-driven rhythms. For a long time, scientists envisioned the “Snowball Earth” scenario as a protracted stall in climate history, where movement and alteration were effectively frozen in place. The outcomes of this fresh investigation are featured in the journal Earth and Planetary Science Letters.
During one of our planet’s coldest eras, ice blanketed continents, oceans, and even tropical latitudes, implying that significant climatic shifts would be all but impossible.
Conversely, a recent piece of research conducted at the University of Southampton paints a much more dynamic picture.
Ancient rock strata unearthed in Scotland display recurring climatic patterns that persisted even amid profound global glaciation, indicating that the climate system never completely ceased activity.
The term “Snowball Earth” refers to the extreme glacial episodes of the Cryogenian Period (roughly 720–635 million years ago), when ice sheets stretched to low latitudes, causing nearly worldwide ocean freezing.
Previously, academics theorized these frozen conditions would cut off interaction between the atmosphere and the ocean, thereby stifling seasonal variations and short-term climate cycles across millions of years.
Researchers tested this assumption by examining thinly layered rocks from the Garvellach Islands, situated off Scotland’s west coast, which originated throughout the Sturtian glaciation—a global deep freeze lasting approximately 57 million years.
Each fine layer, known as a varve, represents sedimentary deposits accumulated over a single year, establishing one of the longest continuous annual climate records discovered from the “Snowball Earth” glaciation period.
By measuring 2,640 layers within the Port Askaig Formation site, the team reconstructed annual environmental conditions, uncovering compelling evidence that climatic rhythms persisted despite the intense global cooling.
“These rocks preserve the full suite of rhythms we recognize today—seasons, solar cycles, and year-to-year variability—all functioning during the Snowball Earth times,” stated Professor Tom Gernon. “This informs us that the climate system has an inherent propensity for fluctuation, even under extreme duress, whenever the slightest opportunity arises.”
Microscopic scrutiny reveals an alternation between lighter and darker bands. The light layers formed from coarser sediments deposited during warmer, melting seasons.
Dark layers stemmed from finer particles settling out during the colder months. This structure aligns with seasonal freeze-thaw cycles.
Beneath the thick ice cover, the water remained tranquil and deep. Floating ice released sediment as it underwent partial thawing. The ice also transported grains that had fallen into the water as melting commenced.
Such consistent patterns strongly support the assertion that sedimentation occurred annually rather than randomly.
“These rocks are extraordinary. They function as a natural data logger, recording climate shifts year after year during one of the coldest periods in Earth’s history,” remarked lead author Chloe Griffin. “Until now, we didn’t know if climate variability could exist at these scales during a Snowball Earth event because no one had found such evidence within the glaciated zone itself.”
Statistical appraisal of the layers’ thickness uncovered recurring climatic cycles, ranging from spans of a few years up to decades and even centuries.
Many of these patterns closely match known solar cycles, including rhythms governed by sunspots, while others resemble oceanic and atmospheric oscillations akin to modern El Niño-like systems.
The solar energy reaching Earth alters minutely over time as cycles of solar activity modify the incoming radiation. Even small variations can impact temperature, ice melt, and sediment movement.
The geological record displays distinct markers corresponding to both decadal and centennial solar rhythms, suggesting that sunlight continued to shape Earth’s climate even during the severe global chill.
Taken together, these findings demonstrate that climatic changes did not vanish but continued, albeit on a reduced scale beneath the ice.
Various “Snowball Earth” scenarios were tested using climate models. A fully frozen ocean suppressed the majority of climatic movement. However, even small patches of exposed tropical water allowed climatic variability to reemerge.
“Our models showed that you don’t need vast open oceans for this. Even restricted areas of open water in the tropics can permit climate regimes similar to what we see today to operate, generating the signals captured in the rocks,” commented study co-author Minmin Fu.
The open water facilitated energy exchange between the air and the ocean. This interaction induced temperature fluctuations and circulation patterns analogous to current climate systems.
Climate change was not the dominant feature of Snowball Earth. The existing evidence points to brief periods of activity lasting perhaps a few thousand years. The vast majority of the Snowball Earth remained intensely cold and steady.
“Our results indicate that this sort of climate variability was the exception rather than the rule,” Gernon explains. “The background state of Snowball Earth was ferociously cold and stable. What we are likely seeing is a fleeting perturbation, lasting millennia, superimposed on a planet that was otherwise deeply frozen.”
The rock formations on Garvella Island represent some of the best-preserved examples globally of “Snowball Earth” geology. Their clear stratification and minimal disturbance allow scientists to examine the climate history of the frozen planet on a near-annual basis.
“These deposits are amongst the best-preserved rock samples characteristic of the Snowball Earth era,” says Elias Rügen. “Thanks to them, we can read the climate history of a frozen planet—in this instance, year by year.”
Gaining insight into such extreme ancient climatic conditions aids scientists in assessing the resilience of planetary climate systems. Even near-total global freezing did not completely halt climatic processes, offering crucial lessons for the future.
“This work helps us understand how resilient, yet simultaneously sensitive, the climate system truly is,” Gernon suggests. “It shows that even under the most extreme conditions the Earth has ever experienced, the system can be set into motion.”
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