Snowball Earth Had Surprisingly Active Climate, Ancient Rocks Reveal

Even during the most extreme ice age in Earth’s history – a period known as “Snowball Earth” – the planet’s climate wasn’t entirely frozen or static, according to new research published in April 1, 2026 in Earth and Planetary Science Letters. Scientists have uncovered evidence of annual, decadal, and centennial climate cycles persisting even when much of the Earth was covered in ice, challenging previous assumptions about the stability of the climate during this period.

The research, led by Dr. Chloe Griffin of the University of Southampton, focuses on rocks from the Garvellach Islands off the west coast of Scotland. These rocks, formed during the Sturtian glaciation – the most severe phase of Snowball Earth, lasting from approximately 717 to 658 million years ago – exhibit remarkably well-preserved layers, known as varves. These layers provide a unique window into the past climate.

“Everyone thought that the climate system would be really quite stable due to global ice coverage,” explained Dr. Griffin. However, the analysis of these varves reveals a surprisingly active climate, with evidence of an at least partially open ocean.

Varves are formed by the seasonal deposition of sediment. During warmer months, glacial meltwater carries coarser sediments into bodies of water. As temperatures drop and meltwater decreases, finer clays are deposited. This creates distinct layers, with each pair of layers potentially representing a single year. The Sturtian rocks examined by Dr. Griffin’s team contain approximately 2,600 of these layer pairs, offering a record spanning 2,600 years.

“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, also from the University of Southampton and a co-author of the study. The preservation of such detailed annual records from this period is considered “unprecedented” by researchers.

The thickness of each layer provides clues about the prevailing weather conditions. Thicker layers suggest greater glacial activity and erosion during warmer periods, while thinner layers indicate calmer, colder conditions. By mathematically analyzing these variations, the researchers identified four repeating cycles. These cycles occurred approximately every 4 to 4.5 layers, 9 layers, 13.7 to 16.9 layers, and 130 to 150 layers.

Remarkably, these cycles correspond to known climate patterns observed today. The 4- to 4.5-year cycle closely resembles the El Niño-Southern Oscillation (ENSO), a climate pattern in the tropical Pacific Ocean characterized by alternating warm (El Niño) and cool (La Niña) phases. The presence of this cycle suggests that some form of heat transport between the ocean and atmosphere was occurring in the tropics, implying the existence of open water, likely near the equator, even during Snowball Earth.

The remaining three cycles are believed to represent variations in the sun’s intensity. While the exact mechanisms driving these cycles during Snowball Earth remain under investigation, the findings suggest that even under extreme glacial conditions, the climate system retained a degree of inherent variability.

Geologist Tony Prave of the University of St. Andrews in Scotland, who was not involved in the study, agrees that the findings are compelling. He notes that the varves from the Garvellach Islands are remarkably similar to those found in modern glacial lakes. “You could go to a glacial lake in Switzerland, look at a core that’s taken out of that lake, and it’ll look exactly like what is preserved in the Garvellach Islands,” he said.

The research contributes to an ongoing debate about the extent and severity of Snowball Earth. Some evidence supports the idea of a completely frozen planet, with minimal interaction between the oceans and atmosphere. However, findings from sites like the Garvellach Islands suggest a more dynamic climate, with localized areas of open water and ongoing climate cycles.

The researchers speculate that short-term warming events, potentially triggered by volcanic activity or asteroid impacts, may have contributed to the observed climate variability. It’s also possible that the analyzed rocks represent periods at the beginning or end of the Sturtian glaciation, when the Earth was partially thawed.

The Sturtian glaciation lasted for approximately 59 million years, and the analyzed layers represent only a small fraction of that time. Further research is needed to determine whether the observed climate cycles were consistent throughout the entire period or were limited to specific intervals. Nevertheless, the findings provide compelling evidence that even during the most extreme ice age in Earth’s history, the climate system was not entirely dormant, and familiar climate patterns continued to operate.