Scottish rocks could hold clues about Earth's past as a snowball

A recent study confirms a European rock formation that extends from Scotland to Ireland likely holds clues about what was once a "snowball Earth."

More specifically, according to a recent statement from the University College London (UCL), researchers are confident the Port Askaig Formation holds a record from Earth's history dating back hundreds of millions of years ago. Scientists believe that, at this time, Earth more or less resembled a snowball due to its climate.

Per the team's analysis, the formation is made up of rock layers as thick as 1.1 kilometers (0.7 miles that date back to the Sturtian glaciation, which occurred between 662 to 720 million years ago. During this period, it's believed that the first of a pair of global freezes occurred, which ultimately led to the creation of multicellular life.

Interestingly, on the island of Garvellachs in the U.K., the researchers say there's a part of the formation that stands out above the others, in that it documents the transition from Earth being more of a tropical planet to an arctic tundra.

Related: Our luscious blue Earth used to be a frozen snowball

"These rocks record a time when Earth was covered in ice," Graham Shields, an Earth Sciences professor at UCL, said in the release. "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 also indicated that the rocks found in the formation fill in a huge piece of our globe's historic jigsaw puzzle.

"The layers of rock exposed on the Garvellachs are globally unique. Underneath the rocks laid down during the unimaginable cold of the Sturtian glaciation are 70 meters [230 feet] of older carbonate rocks formed in tropical waters. These layers record a tropical marine environment with flourishing cyanobacterial life that gradually became cooler, marking the end of a billion years or so of a temperate climate on Earth," Elias Rugen, the study's first author and a Ph.D. candidate at UCL Earth Sciences, said in the statement. "Most areas of the world are missing this remarkable transition because the ancient glaciers scraped and eroded away the rocks underneath, but in Scotland by some miracle the transition can be seen."

Based on the findings, the transition period between the ice's advance and retreat was a process that happened relatively fast (across more than thousands of years) as a result of the albedo effect. For example, if there's more ice, there's an increased amount of sunlight that gets sent back to space.

"The retreat of the ice would have been catastrophic," Shields said. "Life had been used to tens of millions of years of deep freeze. As soon as the world warmed up, all of life would have had to compete in an arms race to adapt. Whatever survived were the ancestors of all animals."

Samples were taken of two layers of sandstone; one from the top of the Port Askaig Formation and a second from the next layer down, the Garbh Eileach Formation. The researchers found highly durable minerals like uranium, known as zircons, within the rock. With this evidence — and after locating other geochemical traces within — the team was able to date the rocks back to more than 60 million years ago. The researchers also now consider this formation as one dedicated to the time when the Cryogenian Period began.

The study was published on Aug. 16 in the Journal of the Geological Society of London.