Scottish sediments challenge long-held view of static climate during planet’s most extreme ice age
Scientists have discovered that Earth’s climate continued to fluctuate during the planet’s most severe ice age, challenging decades of assumptions about the frozen world that existed more than 650 million years ago.
New research from the University of Southampton reveals that even when Earth was locked in a global deep freeze with ice sheets reaching the tropics SciTechDaily, the climate system maintained rhythmic patterns remarkably similar to those observed today.
The breakthrough comes from analyzing ancient layered rocks called varves found on the remote Garvellach Islands off Scotland’s west coast. These sediments formed during the Sturtian glaciation, the most severe Snowball Earth event that lasted 57 million years SciTechDaily, part of the broader Cryogenian Period between 720 and 635 million years ago.
A Natural Data Logger
Lead researcher Dr. Chloe Griffin described the rocks as extraordinary natural archives. The team examined 2,600 individual layers within the Port Askaig Formation, with each thin layer representing a single year of sediment buildup—offering an unprecedented year-by-year record of ancient climate conditions.
Under microscopic analysis, the layers likely formed through seasonal freezing and thawing in a quiet, deep water environment beneath ice SciTechDaily. When researchers applied statistical methods to variations in layer thickness, they uncovered surprising patterns.
Dr. Griffin explained that the team found clear evidence for repeating climate cycles operating every few years to decades, some of which closely resemble modern climate patterns, such as El Niño-like oscillations and solar cycles SciTechDaily.
Climate’s Innate Tendency to Oscillate
Professor Thomas Gernon, a co-author of the study, emphasized the significance of the findings. The rocks preserve what he calls the full suite of climate rhythms known from today—annual seasons, solar cycles, and interannual oscillations—all operating during a Snowball Earth SciTechDaily.
For decades, scientists believed that during Snowball Earth, when the planet resembled a white sphere from space, the climate system essentially shut down. With oceans largely sealed beneath ice, experts assumed atmospheric and oceanic exchanges nearly ceased, preventing short-term climate variations for millions of years.
The new study, published in the journal Earth and Planetary Science Letters, presents a different picture—at least for certain intervals during this frozen epoch.
Not the Norm, But a Window Into Climate Dynamics
The researchers caution that these oscillations were likely exceptional rather than typical. Professor Gernon noted that the background state of Snowball Earth was extremely cold and stable, with this climate variability probably representing a short-lived disturbance lasting thousands of years against the backdrop of an otherwise deeply frozen planet SciTechDaily.
To understand how such variability could occur, the team ran climate simulations. Dr. Minmin Fu, who led the modeling work, found that the models showed conditions needed for these patterns to emerge. According to the research, if even a small portion of the ocean surface—approximately 15 percent—remained ice-free, interactions between ocean and atmosphere could resume, allowing climate oscillations to develop.
Implications for Understanding Climate Resilience
The findings extend beyond ancient history. Professor Gernon emphasized that understanding Earth’s behavior during Snowball Earth reveals important insights about climate system resilience and sensitivity.
The work demonstrates that even in the most extreme conditions Earth has ever seen, the system could be kicked into motion, which has profound implications for how planets respond to major disturbances, including our own in the future SciTechDaily.
Dr. Elias Rugen, who has worked on the Garvellach Islands for five years, called the deposits some of the best-preserved Snowball Earth rocks anywhere in the world, allowing researchers to read climate history one year at a time.
The research was supported by the WoodNext Foundation and represents a significant advance in understanding one of the most dramatic periods in Earth’s climate history—a time that immediately preceded the emergence of the first multicellular organisms and, eventually, the first animals.
As scientists continue to grapple with modern climate change, these ancient Scottish rocks offer a sobering reminder of Earth’s capacity for extreme climate states, while also revealing the climate system’s remarkable ability to maintain dynamic patterns even under the most hostile conditions.