New study shows ancient ‘Snowball Earth’ was not entirely frozen over

GLASGOW, Scotland — Earth’s climate system did not completely shut down during the planet's most extreme ice age, according to new research from the University of Southampton.

The study challenges the long-held "Snowball Earth" theory regarding the period between 720 and 635 million years ago. Scientists previously believed that massive ice sheets covered the entire globe during this era, effectively paralyzing the planet's climate.

The new findings, published in the journal Earth and Planetary Science Letters, are based on an analysis of well-preserved sedimentary rock layers called "varves" located on Scotland's Garvellach Islands. Researchers examined 2,600 individual layers, each representing a single year of geological history.

The analysis revealed repeating climate cycles that mirror modern weather systems. These patterns include solar cycles and fluctuations similar to the modern El Niño phenomenon.

The results indicate that the climate continued to shift on an annual and decadal basis, at least during certain stages of the cryogenic period. Computer simulations included in the study suggest that only about 15% of the ocean surface needed to remain ice-free to sustain these atmospheric and oceanic interactions.

This discovery transcends mere geological academicism; it necessitates a fundamental reconfiguration of our understanding of one of Earth’s most cataclysmic eras. The "Snowball Earth" hypothesis has long been characterized as a period of static, planetary stasis—a dead world locked in a multi-million-year deep freeze. This latest research dismantles that monochromatic narrative, revealing instead a dynamic climate system with an innate propensity for oscillation, even under the most extreme environmental pressures.

The implications of this shift are twofold and profound. First, it provides a more robust framework for the persistence of the biological record. A globally sealed, frozen ocean would have presented a near-insurmountable barrier to early organisms. However, the existence of localized, transient thawing cycles—creating "oases" of open water—would have provided the necessary refugia for microbial life to survive and evolve. This suggests that the foundations for the later explosion of complex life were laid not in spite of the freeze, but within its hidden fluctuations.

Second, the findings offer a critical directive for contemporary climate science and policy modeling. The revelation that the Earth’s climate can "reboot" sophisticated feedback loops, such as El Niño cycles, with only a fraction of the ocean surface ice-free, underscores both the sensitivity and the systemic resilience of the planet. It confirms that the global climate does not operate as a simple binary or an "on-off" switch. Rather, even marginal shifts in the global energy equilibrium can trigger non-linear, complex, and cyclical responses—a reality that must be central to how we model and mitigate climate volatility today.