A rock formation spanning Scotland and Ireland could hold secrets about one of the most dramatic periods in Earth's history—a time when the planet was nearly covered by ice. This fascinating discovery revolves around the Port Askaig Formation, consisting of rock layers up to 1.1 kilometers thick, which scientists believe were formed between 662 and 720 million years ago during the Sturtian glaciation.
The Sturtian glaciation marked the first of two significant global freezes theorized to have played a role in the emergence of complex life. According to the recent studies, one exposed section of rock on the Garvellachs islands showcases the transition from warmer, tropical conditions to the icy landscapes of snowball Earth.
Notably, the unique nature of these rocks lies in their ability to capture the transition, something that's absent from similar age rocks found elsewhere, including parts of North America and Namibia. Researchers are convinced their findings may represent the most comprehensive record of snowball Earth, which suggests the oceans and land were iced over from pole to pole during at least two major cooling events stretching between 2.4 billion and 580 million years ago.
Senior researcher Professor Graham Shields from University College London (UCL) states, "These rocks record a time when Earth was covered in ice." He adds, "All complex, multicellular life, such as animals, arose out of this deep freeze, with the first evidence in the fossil record appearing shortly after the planet thawed."
The study is led by PhD candidate Elias Rugen, who stressed the novel age constraints set for the rocks. He explained how most global formations have lost the tropical layers marking the transition due to glacial forces scraping them away, except for the fortunate occurrences seen in Scotland.
With the Sturtian glaciation lasting around 60 million years, it was one of the critical cold snaps during the Cryogenian Period, which lasted from 635 to 720 million years ago. Before this era, life predominantly consisted of single-celled organisms and algae, with complex multicellular life only emerging following thawing periods after intense cold.
Some theories suggest the harsh conditions may have pushed single-celled organisms to work together, leading to the evolution of multicellular life. Add to this the fascinating dynamics of ice, where the retreat and advance occurred rapidly, likely due to what scientists call the albedo effect—more ice means more sunlight reflects back, and vice versa.
Professor Shields elaborates on the consequences of warming by saying, "The retreat of the ice would have been catastrophic. Life had been used to tens of millions of years of deep freezing, so as soon as the world warmed, all known life had to adapt rapidly to new conditions."
The research team took samples from the Port Askaig Formation, including those from the underlying Garbh Eileach Formation, which is 70 meters thick. They believe this newfound knowledge about the rock's age could be pivotal for designations as a Global Boundary Stratotype Section and Point (GSSP), otherwise known as a golden spike, which marks significant geological boundaries.
These sites are not just scientific landmarks; they can attract visitors from around the globe intrigued by Earth’s geological history. The study's findings were published recently in the Journal of the Geological Society of London, marking an important milestone not only for the researchers but for our collective comprehension of Earth's icy past.
