¿Was the Earth a “snowball”? This theory, named precisely like this: Snowball Earthpredicts that between 720 and 635 million years ago our planet was completely frozen, with ice sheets miles thick from the poles to the equator. However, consistent facts supporting this thesis have been lacking, at least until now. Last week, a team of geologists at the University of Colorado Boulder claimed to have found the first physical evidence of Snowball Earth: “filaments” of ‘Tava sandstone’ (a particular type of rock) that appear to have been forced into the granite from the Front Range of the Rocky Mountains, in Colorado, USA. The study public in the magazine Proceedings of the National Academy of Sciences.
At one time, experts explain, Colorado was not in North America, but was part of an ancient continent called Laurentiaand was located in equatorial latitudes. Therefore, studying its geology could reveal the secrets of our planet’s long existence, even before life developed.
Looking in particular at the rocks of Pikes Peak, the highest peak in the Front Range, the researchers wanted to know the origin of the so-called ‘Tava injections’, that is, veins of solidified sand inside the granite typical of this area. They look, in effect, like infiltrations, as if this foreign material had been injected at very high pressure. The scientists’ hypothesis is not far from this image: it is possible that a mixture of sand and water from the surface was pushed into the granite by the pressure developed by the thick layers of ice above. Something similar continues to happen today under the ice of Antarctica, for example.
This is a fascinating idea, but when would they have been formed these injections? To date them, geologists had to resort to an indirect method. They identified filaments of ferruginous minerals that crossed the Tava injectites at different points and dated them using a technique called ablation mass spectrometry laser. Iron minerals (they explain the authors in The Conversation) contain very low amounts of naturally occurring radioactive elements, such as uraniumwhich slowly decomposes into lead at a known rate. Measuring the proportion of uranium and lead isotopes, it was possible to trace the age of formation of the crystals and thus define a time interval for the formation of injectites of tava. This time interval is It dates back to 690 and 660 million years ago.when Colorado was at the equator, and thus supports the Snowball Earth theory.
The work is not finished; If these injections formed in Colorado during the Snowball Earth phase, they probably also formed in other places of North America. “We want to spread the word,” said Liam Courtney-Davies, lead author of the study, “so that others can try to find these features and help us build a more complete picture of Snowball Earth.”
Article originally published in WIRED Italy. Adapted by Mauricio Serfatty Godoy.
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