HONG KONG: The second ice age during the Cryogenian period was not followed by the sudden and chaotic melting-back of the ice as previously thought, but ended with regular advances and retreats of the ice, according to research published by scientists from the University of Birmingham in the journal Nature Geoscience today.
The researchers also found that the constant advance and retreat of ice during this period was caused by the Earth wobbling on its axis.
These ice ages are explained by a theory of Snowball Earth, which says that they represent the most extreme climatic conditions the world has ever known and yet they ended quite abruptly 635 million years ago. Little was known about how they ended – until now.
For the study, the scientists analysed sedimentary rocks from Svalbard, Norway that were laid down in that ice age. The deposits preserved a chemical record which showed high levels of CO2 were present in the atmosphere. Carbon dioxide was low when the ice age started, and built up slowly over millions of years when the whole Earth was very cold – this period is represented only by frost-shattered rubble under the sediments.
Eventually the greenhouse warmth in the atmosphere from carbon dioxide caused enough melting for glaciers to erode, transport and deposit sediment. The sedimentary layers showed ice retreat and advance as well as cold arid conditions. They reveal a time when glacial advances alternated with even more arid, chilly periods and when the glaciers retreated, rivers flowed, lakes formed, and yet simple life survived.
As theory predicts, this icy Earth with a hot atmosphere rich in carbon dioxide had reached a ‘Goldilocks’ zone – too warm to stay completely frozen, too cold to lose its ice, but just right to record more subtle underlying causes of ancient climate change.
