Dienstag, 14. April 2015

Planet Earth deep frozen

     It is probable that for several times planet earth was completely covered by ice, geologists say. From a distance, it would have looked like a huge snowball. A new study from the University of Göttingen now confirms that the Earth went through episodes of extremely cold climates millions and billions years ago. In so-called “Snowball Earth” periods, glaciers even covered equatorial regions. Geologist Dr. Daniel Herwartz has reconstructed the oxygen isotopic compositions of ancient (sub) tropical glaciers. The results are published in Proceedings of the National Academy of Sciences of the USA (PNAS) on April 13, 2015.


New Study confirms periods with extremely cold climate – Glaciers covered even equatorial regions

(pug) It is probable that for several times planet earth was completely covered by ice, geologists say. From a distance, it would have looked like a huge snowball. A new study from the University of Göttingen now confirms that the Earth went through episodes of extremely cold climates millions and billions years ago. In so-called “Snowball Earth” periods, glaciers even covered equatorial regions. Geologist Dr. Daniel Herwartz has reconstructed the oxygen isotopic compositions of ancient (sub) tropical glaciers. “The oxygen isotope composition of the glaciers can provide information about the climate conditions on an earth totally covered by ice”, says Dr. Herwartz, who is the lead author of the study in Göttingen and who now works at the University of Cologne. The results are published in Proceedings of the National Academy of Sciences of the USA (PNAS) on April 13, 2015.
The studied rocks, 2.4 billion and 700 million years old, were samples from north-western Russia and China. At the time, both regions were located close to the equator. There, the rocks interacted with melt water from (sub) tropical glaciers and stored the provided isotopic information for hundreds of millions years.

The reconstructed oxygen isotope composition for the glaciers of the 2.4 billion year event is similar to one that is nowadays only observed in the coldest place of our planet: in central Antarctica with mean annual temperatures of minus 40 degree Celsius. “To imagine places like Egypt or Florida with mean annual tem-peratures of minus 40 degree Celsius is just mind-boggling, but that is what the data suggests” says Dr. Herwartz. The 700 million year old rocks from China conform to climates similar to southern Greenland today and suggest a much warmer climate than the 2.4 billion year old rocks from north-western Russia. The scientists were able to reconstruct the glacial water isotopic compositions by analysing the 17O isotope with a highly precise method.

The “Snowball Earth” hypothesis poses that the entire earth was frozen with all oceans covered under sev-eral hundred meter thick sea-ice. At low CO2 levels ice caps extend to lower latitudes and once, a critical part of the Earth’s surface is covered by ice, reflection of sunlight leads to a further decrease in temperature and ends in an entirely frozen planet. Only the raise of atmospheric CO2 through continuing volcanic activity could enforce a competing greenhouse effect and released the Earth from it’s frozen state. “’Snowball Earth’ events are critical intervals in the evolution of life. While an entirely frozen planet restricts live to small enclaves like hot springs, the times after such events often show an unseen explosion of live.” says co-author Prof. Dr. Andreas Pack from the University of Göttingen.

Original publication:
Herwartz D., Pack A., Xiao Y., Muhlenbachs K., Sengupta S. and Di Rocco T.(2015): Revealing the climate of snowball Earth from Δ17O systematics of hydrothermal rocks. Proceedings of the National Academy of Sciences of the USA. Doi: 10.1073/pnas.1422887112
Romas Bielke ÖffentlichkeitsarbeitGeorg-August-Universität Göttingen


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