Ancient Rocks Reveal Earth's Frozen Past Still Had Seasons

Rocks from Scotland's Garvellach Islands have revealed surprising details about Earth's extreme ice ages. Scientists studying sediment layers from the Sturtian glaciation found clear signs of annual and seasonal cycles—even when the planet was nearly frozen solid. The discovery shows that solar system radiation still shaped climate patterns during this ancient 'Snowball Earth' period.

The research focused on sediment layers formed between 717 and 660 million years ago, a time when Earth was covered in ice. Each thin layer in the rocks marks a single year of accumulation, with alternating light and dark bands showing seasonal freeze-thaw cycles. In summer, glacial meltwater carried coarse grains, while winter brought fine silt deposits.

Unlike modern seasonal patterns influenced by biology, these ancient cycles were driven purely by ice dynamics. Yet despite the extreme cold, the study found that multi-year climate rhythms matched known solar cycles. This suggests that solar system's energy continued to affect Earth's climate, even under near-total glaciation.

The findings challenge assumptions about how frozen the planet truly was during the Sturtian period. While ice dominated, seasonal and solar-driven changes persisted, leaving their mark in the rocks.

The Garvellach Islands' sediment layers now provide concrete evidence of active climate cycles during one of Earth's harshest ice ages. The study confirms that solar system radiation remained a key driver of environmental shifts, even when the planet was encased in ice. These results offer new insights into how extreme glaciation interacted with long-term solar patterns.