Researchers have discovered evidence for an ancient glaciation in old Caledonian rocks – a previously undiscovered finding which indicates that the planet froze over during the ‘Snowball Earth’ period nearly 700 million years ago.
The discovery, by geologists at the University of St Andrews, is the first proof that the archetypal Snowball Earth (Cyrogenian) period affected areas in Britain and Ireland.
The Snowball Earth theory, a term coined by geologists in 1992, proposed that the Earth was completely covered in ice for as long as ten million years. Signs of extensive glaciers at sea level in the tropics over 600 million years ago, which appear to defy current understanding of climate change, have perplexed geologists for decades and the theory is hotly contested by scientists.
Drs Tony Prave and Ian Alsop, alongside research student Gillian McCay (now at Edinburgh University), made the discovery of Snowball Earth glaciations during fieldwork in Donegal, Ireland, an area that is part of the ‘Caledonian chain’ forming the Scottish-Irish Highlands.
Dr Prave said, “This work represents the first documentation of the archetypal Snowball Earth glaciation in that region and thus places Eire-UK firmly into the global network of regions in which evidence for this event has been found.”
The broad band of ancient rocks, which are part of a much larger ancient mountain belt that formed some 400-450 million years ago, record the evolution of the Earth during “Deep Time” approximately 700 million years ago. The remnants of the Caledonian chain occur along the North East margin of North America, through the north of Ireland and northern Britain and into Scandinavia. The Snowball Earth model has been the subject of lively debate over the past decade because, if accurate, it reveals that the Earth System experienced unprecendented periods of cold climates followed by ultra greenhouses.
Dr Prave explained, “This glaciation was global in extent, vastly exceeding the glaciations in Earth’s recent history. The period of time during which this occurred is the focus of intense international research because some of the most profound events to shape the modern Earth System happened then, including the advent and evolution of multicellular life, extraordinarily severe climate change and wholesale plate tectonic reorganisation of Earth’s land surface.
He continued, “Documenting these key events is crucial to enhance understanding of Earth System behaviour in general and to the nature of extreme climate change during Deep Time. Even though this all happened a long time ago, it provides a case study of how the Earth System responds to periods of extreme environmental change and can thereby provide clues as to what drives the climate system in lieu of the potential effect that humans have in influencing climate change.”
The discovery is published in the November issue of the prestigious international journal Geology.
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