Climate Rhythms in a Frozen World
During Snowball Earth's Sturtian glaciation (720-635 million years ago), ice sheets reached the tropics. Yet ancient rocks on Scotland's Garvellach Islands preserve 2,600 annual layers — varves — that reveal the planet still had climate rhythms. Scientists found El Nino-like oscillations, decadal patterns, and solar cycle signatures. These signals only appear in a "slushball" state where ~15% of the ocean remains ice-free, allowing atmosphere-ocean interactions. Tropical oases may have sheltered early life through Earth's most extreme ice age.
Griffin, Rugen, Fu & Gernon — Earth and Planetary Science Letters, 2026
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