The research indicates that the Port Askaig Formation, which features rock layers that can reach up to 1.1 km in thickness, was likely formed during the Sturtian glaciation, between 662 and 720 million years ago. This event is recognized as the first of two significant global ice ages that are believed to have contributed to the emergence of complex multicellular life.
A geological formation that stretches across Ireland and Scotland might hold the most extensive evidence of “snowball Earth,” a vital chapter in Earth’s history when the planet was enveloped in ice, according to a recent study conducted by researchers at UCL (University College London).
Published in the Journal of the Geological Society of London, the study reveals that the Port Askaig Formation consists of rock layers up to 1.1km thick, likely deposited during the Sturtian glaciation approximately 662 to 720 million years ago, marking a time of significant global cooling believed to be crucial for the rise of complex, multicellular life.
One significant rock outcrop located on the Garvellachs, a group of Scottish islands, uniquely illustrates the shift into the “snowball Earth” phase from a previously warm, tropical climate.
In contrast, other rock formations from the same period in locations like North America and Namibia lack evidence of this transition.
Professor Graham Shields, a senior researcher at UCL Earth Sciences, remarked, “These rocks tell the story of a time when Earth was completely covered in ice. The complex multicellular organisms, including animals, emerged from this severe ice age, with fossil evidence appearing soon after the planet began to warm.”
Elias Rugen, the first author and a PhD student at UCL Earth Sciences, noted, “Our research provides the first definitive age benchmarks for these rocks in Scotland and Ireland, highlighting their global importance.”
“The rock layers visible on the Garvellachs are truly one of a kind. Beneath the layers formed in the extreme cold of the Sturtian glaciation lie 70 meters of older carbonate rocks made in tropical waters. These layers reflect a vibrant marine ecosystem that gradually became cooler, marking the end of a prolonged era of temperate climate on Earth.”
“Many regions around the world lack this extraordinary transition, as ancient glaciers have eroded the underlying rocks; however, this exceptional transition can be observed in Scotland, almost like a miracle.”
The Sturtian glaciation stretched over about 60 million years and is one of two significant ice ages that occurred during the Cryogenian Period, approximately between 635 and 720 million years ago. Before this era, life was primarily made up of single-celled organisms and algae.
Following this glaciation, complex life forms arose relatively quickly in geological terms, and many modern animals share fundamental traits with life forms that developed over 500 million years ago.
One hypothesis suggests that the harsh conditions of extreme cold may have driven the development of altruism, as single-celled organisms began to cooperate, leading to the evolution of multicellular organisms.
The advance and retreat of global ice were likely swift, taking place over thousands of years due to the albedo effect—where the presence of ice reflects more sunlight back into space and vice versa.
Professor Shields elaborated: “The ice retreat would have been catastrophic. Life had adapted to millions of years in a freezing environment, and as the planet warmed, all life forms would have been pressured to compete for survival. The organisms that persevered are ancestors to all animals today.”
In this study, the research team gathered sandstone samples from the 1.1 km thick Port Askaig Formation and the older 70-meter thick Garbh Eileach Formation underneath it.
They examined tiny, durable minerals known as zircons within the rock, which can be accurately dated due to their radioactive uranium content, which decays into lead at a constant rate. The zircons, combined with other geochemical data, indicate that the rocks were deposited between 662 and 720 million years ago.
According to the researchers, these new age estimates for the rocks could serve as critical evidence for recognizing the site as a benchmark for the beginning of the Cryogenian Period.
This benchmark, referred to as a Global Boundary Stratotype Section and Point (GSSP), is often called a golden spike because a gold spike is inserted into the rock to define the boundary.
GSSPs draw international attention, and in some cases, museums are established at these locations.
A team from the International Commission on Stratigraphy, part of the International Union of Geological Sciences, visited the Garvellachs in July to evaluate the site for potential designation as a golden spike. At present, the islands can only be accessed by chartering a boat or by sailing or kayaking to them.
The research was carried out by teams from UCL, the University of Milano-Bicocca in Italy, and Birkbeck University of London, with funding provided by the Natural Environment Research Council (NERC).
