A recent study conducted by researchers from UCL (University College London) has found that a rock formation spanning Ireland and Scotland may be the most complete record of “snowball Earth,” a crucial moment in planetary history when the globe was covered in ice. The Port Askaig Formation, which consists of layers of rock up to 1.1km thick, is believed to have been laid down between 662 to 720 million years ago during the Sturtian glaciation. This period marked the first of two global freezes that are thought to have led to the development of complex, multicellular life on Earth.
One unique aspect of the Port Askaig Formation is that it shows the transition into “snowball Earth” from a previously warm, tropical environment. This transition is missing in other rocks that formed around the same time in different parts of the world, such as North America and Namibia. The exposed outcrop of the formation on the Scottish islands of Garvellachs provides valuable insights into the conditions that existed during this critical period in Earth’s history.
The Sturtian glaciation lasted approximately 60 million years and was one of two major freezes that occurred during the Cryogenian Period between 635 and 720 million years ago. Prior to this period, life on Earth consisted mainly of single-celled organisms and algae. The extreme cold of the glaciation may have prompted the emergence of complex life forms through the development of altruism, as single-celled organisms learned to cooperate with each other, leading to the evolution of multicellular life.
The study involved the analysis of samples of sandstone from the Port Askaig Formation as well as from the older Garvh Eileach Formation underneath. By studying tiny, durable minerals called zircons in the rock, which contain the radioactive element uranium, the researchers were able to accurately date the rocks to between 662 and 720 million years ago. These new age constraints may provide the evidence needed for the site to be declared as a marker for the start of the Cryogenian Period, known as a Global Boundary Stratotype Section and Point (GSSP) or “golden spike.”
GSSPs are important markers in geological history and can attract visitors from around the world to study and learn about significant events in Earth’s past. A group from the International Commission on Stratigraphy visited the Garvellachs in July to assess the site for a potential golden spike designation. Currently, the islands are only accessible by boat, sailing, or kayaking. The research team involved in the study included researchers from UCL, the University of Milano-Bicocca in Italy, and Birkbeck University of London, with funding from the Natural Environment Research Council (NERC).
