Scientists from the University of Southampton have discovered evidence that during the most extreme ice age, called Snowball Earth in the Cryogenian period (720 to 635 million years ago), the Earth's climate system did not completely stop.[1] The rocks under study act as a natural recorder, recording annual climate changes during one of the coldest phases of Earth's history.[1] The microscopic layers in these rocks were formed by seasonal cycles of freezing and thawing in calm deep waters beneath the ice sheet.[1] Statistical analysis of the differences in the thickness of the layers revealed repeated climatic cycles lasting several years to decades.[1] Some of these cycles resemble contemporary patterns, such as El Niño-like oscillations and solar cycles.[1] However, this climate variability was not the rule, but the exception—probably a short-term disturbance lasting thousands of years against the background of the extremely cold and stable state of the planet.[1]