For nearly 60 million years, our home planet would have been frozen like a giant snowball.
Now scientists have discovered evidence of how Earth transformed from a tropical underwater world teeming with photosynthetic bacteria to a frozen wasteland, all preserved within the massive rock formations that make up the islands of Scotland and Ireland.
A team led by researchers at University College London (UCL) examined more than 2,000 zircon grains from 11 sandstone samples taken from depths of up to 200 metres in the 1.1 kilometre (0.7 mile) thick Port Askaigs Formation and the 70 metre-thick, older Gharb Eleh Formation beneath it.
These formations are part of: Daladian Supergroup A geological chain extending from Donegal in Scotland and Ireland to Ireland Northeast line The researchers found evidence starting in central Scotland, exposed on the surface in places like the Scottish island of Garve Eilech.
Zircon grains deposited in sedimentary layers can be used to determine the age of the rock layer. As zircons are formed, Reject all lead While embedded in the structure, it always contains a certain amount of uranium, so it eventually decays to lead at a certain rate, even if it is embedded in zircon, which hates lead.
So the lead found in the zircon represents the decay of uranium, which is a wonderful record of the passage of time.
The technique revealed that the rocks in the Port Askaig and Gharb Eleh formations were deposited between 720 and 662 million years ago, during a time when the Earth experienced rapid climate change known as the Stutt Ice Age.
This was the first of two ‘freezes’ that occurred worldwide. It may have signaled the beginning of multicellular life on EarthSo it’s exciting (not to mention convenient) to find a well-preserved geological archive from this era so close to the surface.
“Our study provides the first definitive age constraints on these Scottish and Irish rocks, confirming their global importance.” Say Elias Rugen, PhD student in Earth Sciences at UCL.
Older layers of carbonate rock formed in tropical seas before the upper layers of rock were deposited during the “unimaginable cold” of the Sturtian Ice Age, which some believe was a Snowball Earth event. explain.
“These layers record a tropical marine environment that was home to a thriving blue-green algae lifeform, and a gradual cooling that marks the end of Earth’s temperate climate, which lasted about a billion years.” Say.
“In most parts of the world, this amazing transformation is not happening because ancient glaciers have scraped and eroded the rock underneath. But in Scotland, the transformation has been miraculous.”
The age limit defined for this rock means that the site can be marked as an official starting point. Cryogenian period.
“These rocks record a time when the Earth was covered in ice. All complex multicellular life, such as animals, arose from this deep freeze, and the first evidence of the fossil record appears shortly after the Earth thawed.” Say UCL geochemist Graham Shields.
“If the ice had retreated, it would have been catastrophic. Life had been accustomed to extreme cold for tens of millions of years. As soon as the world warmed, all life would have had to compete in an arms race to adapt. The ones who survived were the ancestors of all animals.” Say shield.
This study was published in: Journal of the Geological Society of London.
