The Port Askaig Formation, spanning Ireland and Scotland, contains a remarkably complete record of the 'Snowball Earth' period.
The formation consists of rock layers up to 1.1 kilometers thick.
The rocks were deposited between 662 and 720 million years ago during the Sturtian glaciation.
It was the first of two global freezing events believed to have spurred the evolution of complex life.
Unlike other rocks from the same period, the Port Askaig Formation provides a continuous record of this crucial transition.
Snowball Earth is a geological hypothesis suggesting that at least twice in Earth's history, the entire planet's surface became nearly entirely frozen over, with ice extending from the poles to the equator.
This extreme cooling event is believed to have occurred during the Cryogenian period, approximately 720 to 635 million years ago.
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