New evidence for "Snowball Earth"
Detection of ice in the tropics 716.5 million years agoRead out
There was probably a time when the earth was almost completely iced - a so-called "snowball earth" event. This is confirmed by new rock analyzes, which American geologists have now introduced in "Science". The data shows for the first time that our planet was covered with ice 716.5 million years ago, far into the tropics.
For a long time, geologists and climatologists have been arguing about the hypothesis of a "snowball earth". According to that, in the age of the earth, in a time phase about 750 to 600 million years ago, almost the entire earth was covered with ice for some time. The evidence for this, however, are so far very contentious. Now scientists from several American universities have supplied new, sensational data. The researchers studied rock strata from the Earth Antiquity in northwestern Canada and discovered glacial deposits and other signs of icing, such as formations with typical furrows, ice debris and deformation of soft sediments. Dating revealed an age of 716.5 million years for these strata.
Icy to the tropics
But the sensational thing was magnetic measurements and further analyzes. They revealed that these rocks were not at the Arctic Circle at the time, but in the tropics. "This is the first time that the Sturt icing has been detected in tropical latitudes, " explains Francis A. Macdonald, lead author of the study and assistant professor of geosciences at Harvard University. "This provides direct evidence that this icing was a 'snowball earth' event. Our data also indicate that the Sturtic Ice Age lasted at least five million years. "
"Because of the high albedo of the ice, climate models have long predicted that the entire ocean would freeze very quickly when sea ice develops within the 30-degree latitude to the equator, " the researcher continued. "Therefore, our result indicates very strongly that there must have been ice in all latitudes in the Sturt icing."Yukon Territory in Canada Francis A. Mcdonald / Harvard University
Volcanism as the trigger or end point?
It is not yet known exactly what triggered this icing period and what ended it, but in the opinion of Macdonald volcanic forces may have played a role. The 716.5 million year now identified as icing is relatively in line with that of a vast volcanic area, a so-called "large igniteous province" that spans more than 1, 000 kilometers Alaska to Ellesmere Iceland in northeastern Canada. Thus, the icing may have been triggered or terminated by this volcanic activity. display
Eukaryotes survived icing
However, the conditions must have enabled the survival of eukaryotic creatures virtually our distant ancestors during the great icing. Because that is proven by fossil finds. It is also known that animal life developed immediately after the end of this icing. "Fossil findings indicate that all large groups of eukaryotes, with the exception of animals, existed before icing, " Macdonald said. This leads to the question: If there was a snowball earth, how did these eukaryotes survive? Sturt icing may even have stimulated the evolution and development of animals?
According to the researchers, the development of organisms during this period shows that there must have been sunlight and liquid water somewhere in the earth during the period of icing. Even in the case of a snowball, according to Macdonald, there must have been temperature gradients, and presumably the ice has also been dynamic: flowing, expanding, and in places with open spaces that represented a sanctuary for life.
(Harvard University, 10.03.2010 - NPO)