Out for "Snowball Earth"?

New evidence of open water and warm periods in supposedly global cooling

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Was there a time when the whole earth was covered in ice? According to the hitherto common theory of the "Snowball Earth" this was the case some 850 to 544 million years ago. However, new data published in the journal Geology have revealed the existence of warm periods even during this long ice age.

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Using the method of the so-called chemical alteration index, Swiss and British scientists investigated the chemical and mineral composition of sedimentary rocks in Oman. The formations of the Huqf group date back to the so-called cryogenic period 850 to 544 million years ago. The index provides information on climatic changes through the chemical weathering of the rocks: weathering at the soil surface is more intense in warm humid periods, and the original rock composition remains virtually unchanged under cold, dry conditions.

Warm periods despite the cold period

The scientists found three periods with extremely low weathering rates in these analyzes and thus clear evidence of phases of great cold. But these chill times alternated with periods when the chemical weathering was obviously much higher - an indication of interglacial phases with warmer climates. Apparently at that time in some areas open, not frozen ocean existed. Thus, these data are in contradiction to the snowball theory, according to which the earth's surface should be completely frozen and covered by glaciers and ice.

"If the earth had been completely frozen for a long time, these climatic cycles would not exist - the earth would have turned into a barren world with almost no weather. Because there would be no evaporation from the sea and little snowfall, "explains the lead author of the study, Professor Philip Allen of Imperial College in London. "Once completely frozen, it's actually hard to create the right conditions that would allow melting. Because the incident solar radiation would be reflected by snow and ice. The evidence of climatic changes is therefore a contradiction to the theory of the snowball earth. "Display

Climate system under extreme conditions

"This is not just about the past. We live in a time of climate change and there is a big debate about how far the natural variability of the climate goes, "said Allen. "The knowledge of climate change in primeval times gives us clues about how our climate system works under extreme conditions."

In his view, however, these extreme conditions were not a complete freezing of the entire earth at that time. "The challenge of snowball theory opens up fascinating questions about how Earth managed to get so close to a global climate catastrophe, but then escaped it, " Allen said. Obviously, open water played a crucial role in the tropical seas.

"It was the strongest glaciation the planet has experienced in the last billion years and the big question is: how could the ice have reached the tropics and then not covered everything?" The researcher explains. "The total icing that we came so close to at that time would have given an extreme blow to early life and probably set the course for a completely different evolutionary path. The reasons for this near-disaster remain one of the questions that science still has to answer. "

(Imperial College London, 26.03.2007 - NPO)