Earth wasn’t always a covered with lush greenery and glorious blue oceans teeming with life.
In fact, around 700 million years ago it was a shimmering ‘snowball’, an ice planet worthy of Star Wars.
Now scientists say geological relics of ‘Snowball Earth’ still exist across Scotland and the north of Ireland.
Rocks along a massive 200-mile formation – which straddles the North Channel – date back to the Snowball Earth era, they claim.
After about 60 million years as an ice planet, Earth eventually unfroze, allowing the right conditions for life as we know it today to thrive.
Roughly 700 million years ago, our planet plunged into a dramatic deep freeze that lasted millions of years, creating what’s come to be known as ‘Snowball Earth’ (artist’s impression)
Around 700 million years ago, Earth was a shimmering ‘snowball’, an ice planet worthy of Star Wars. Pictured, the planet ‘Hoth’ from ‘Star Wars – The Empire Strikes Back’ (1980)
‘These rocks record a time when Earth was covered in ice,’ said Graham Shields, a professor of geology at University College London.
‘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.’
Earth’s ‘big freeze’ around 700 million years ago – which gave it the appearance of a giant ‘snowball’ – is an event known as the Sturtian glaciation.
This frigid transformation was likely triggered by historically low carbon dioxide emissions from volcanoes, scientists think – essentially leading to the reverse of today’s ongoing greenhouse effect.
Port Askaig Formation – composed of layers of rock up to 0.68 miles (1.1km) thick – was likely ‘laid down’ during the Sturtian glaciation, the authors of this study say.
‘The Port Askaig Formation is a sedimentary rock formation so was deposited as horizontal layers,’ co-author Elias Rugen, a PhD candidate at UCL, told MailOnline.
‘Sedimentary rocks, such as those deposited beneath glaciers, are deposited (or laid down) horizontally.’
This map locates the main outcrops of the Port Askaig Formation as red dots. Port Askaig Formation sits within a much larger volume of rock called the Dalradian Supergroup (shaded in green) that contains rocks that are both older and younger than the Port Askaig Formation
One exposed outcrop of Port Askaig Formation is found on Scottish islands called the Garvellachs (pictured)
For the study, the researchers collected samples of sandstone from Port Askaig Formation and analysed tiny, extremely durable minerals in the rock called zircons.
These can be precisely dated as they contain the radioactive element uranium, which converts (decays) to lead at a steady rate.
The zircons together with other geochemical evidence suggest the Port Askaig rocks were deposited between 662 and 720 million years ago – coinciding with the estimated date range for the Sturtian glaciation.
‘These are the first direct ages we have for these rocks which places the deposition of the Port Askaig Formation during a snowball Earth glaciation episode in Earth’s history,’ Professor Shields told MailOnline.
Port Askaig not only offers the first rocky evidence of ‘Snowball Earth’ in Britain, but it may also be the world’s most complete record of the global freeze.
Anthony Spencer, co-author of the latest study, stands on glacial till (sediment deposited by a glacier) of the Port Askaig Formation on Garbh Eileach, the largest of Scotland’s Garvellach islands
Of course, Snowball Earth eventually melted as carbon emissions gradually increased as volcanic activity increased again.
‘Once the snowball melted, there would have been a catastrophic change in circumstance for all forms of life that had adapted to the extreme cold,’ Professor Shields told MailOnline.
‘Among the winners of that arms race would have been the early ancestors of all animal life on Earth today.
‘Other forms of complex multicellullar life (modern types of algae, for instance) also emerged around this time.
‘So this juncture represents the transition out of microbially-dominated ecosystems into a more complex, modern-seeming living world.’
The study has been published in the Journal of the Geological Society of London.
