The Irish-Scottish rock formation may be a rare record of the 'Snowball Earth’ period Geography

A rock formation spanning Ireland and Scotland may be a rare record of a „Snowball Earth” — a pivotal moment in planetary history when the globe was covered in ice.

The research suggests that the Port Askig Formation, composed of 1.1 km (0.7 mi) thick layers of rock, was probably laid down between 662 m and 720 m years ago during the Sturtian glaciation. It was the first of two global freezes thought to have triggered the development of complex life.

According to the study, a section of exposed rock found in Scotland’s Carvellaux Islands is unique because it shows the transition from a previously warm, tropical environment to a snowball Earth. Other rocks formed at the same time, some in North America and Namibia, do not show this change.

As such, the researchers believe their findings may be the most complete record of the snowball Earth’s history – during at least two extreme cooling events between 2.4bn and 580m when Earth’s oceans and land surfaces were covered in ice from the poles to the equator. years ago.

Senior author Professor Graham Shields of Earth Sciences, University College London (UCL), said: „These rocks record a time when Earth was covered in ice. All complex, multicellular organisms such as animals arose from this deep freeze, with the first evidence in the fossil record appearing shortly after the planet thawed.

First author Elias Rugen, PhD candidate in UCL Earth Sciences, said: „Our study provides the first firm age constraints for these Scottish and Irish rocks, confirming their global importance.”

Much of the world is missing layers of rock that record tropical climates and indicate change because ancient glaciers eroded away the underlying rocks. „But in Scotland, by some miracle, we may see change,” Rugan said.

Lasting about 60 Ma, the Sturtian Glacier was one of two major glaciations that occurred during the Cryogenian Period, between 635 Ma and 720 Ma. For billions of years before this, life consisted only of single-celled organisms and algae. After this period, complex life emerged rapidly, and most animals today resemble in basic ways life forms that evolved more than 500 million years ago.

One theory is that the hostile nature of extreme cold may have prompted single-celled organisms to cooperate with one another, creating multicellular life.

Because of the albedo effect, the advance and retreat of ice across the planet is thought to have happened relatively quickly, over thousands of years—that is, the more ice, the more sunlight reflected back into space, and vice versa. .

Shields said: „The retreat of the ice would have been catastrophic. Life was used to the deep freeze for tens of thousands of years. As the world warmed, all life would have had to compete in an arms race to adapt. The survivors were the ancestors of all animals.

For the study, the research team analyzed samples of sandstones from the Port Askig Formation and the underlying, older, 70-meter-thick Curb Eleach Formation.

The researchers said the new age constraints for the rocks could provide the evidence they need for the site, which has been heralded as a marker for the start of the Cryogenian period. Known as the Global Boundary Stratum Section and Point (GSSP), this marker is sometimes referred to as a golden spike – a golden spike driven into the rock to mark the boundary – and these sites attract visitors from around the world.

The study, led by UCL researchers, is published in the Journal of the Geological Society of London.