A new radioactivity model of the Earth's ancient rocks is calling into question current models for the formation of the Earth's continental crust, suggesting that continents rose from the sea much earlier than thought, but were destroyed and left few traces.
University of Adelaide scientists have published over two billion years two studies on a model of rock radioactivity, which found that the Earth's crust could have been thicker, much earlier than current models suggest, with continents possibly already four Billions of years.
"We use this model to understand the evolution of processes from early Earth to the present, suggesting that the survival of the early crust depended on the amount of radioactivity in the rocks ̵
"If our model proves correct, many aspects of our understanding of Earth's chemical and physical evolution may need to be revised, including the rate of growth of the continents and possibly even the onset of plate tectonics."
Dr. Hasterok and his Ph.D. Student Matthew Gard compiled 75,800 geochemical samples of magmatic rocks (such as granite) with valued educated ages from all continents. They estimated the radioactivity in these rocks today and created a model of average radioactivity from four billion years ago to today.
"All rocks contain natural radioactivity, which generates heat and raises temperatures in the crust as they decay – the more radioactive a rock is, the more heat it produces," says Dr. Hasterok. "Rocks that are typically associated with the continental crust have higher levels of radioactivity than oceanic rocks, and a four-billion-year-old rock would have about four times more radioactivity than it does today."
Radioactivity in rocks older than about two billion years. If they corrected for higher heat generation, the deficit disappeared due to the higher levels of radioactivity that would have been present.
"We believe that there were more granite or continental rocks, but due to the higher radioactivity and thus higher heat melted or were easily destroyed by tectonic movements, which is why these continental crust do not occur in the geological records.
However, we believe that much earlier there has been a significant amount of, albeit very unstable, continental crust. "
Co-author Professor Martin Hand, also from the University of Adelaide, says the new model important implications for monitoring the impact could be global warming.
"With this new model we can predict the radioactivity of rocks in places where we have few or no samples, as in the Antarctic, where we have no access to samples, which is very important for the assessment of stability "The researchers say that the new radioactivity model can also be helpful in the search for hot rocks with geothermal potential and geothermal energy," said Martin Hand, Professor of Earth Sciences, to use more accurate models of oil maturation in sedimentary basins.  The studies were published in the journals Precambrian Research and Li thos .
Researchers discover missing ingredients from the earth's crust
D. Hasterok et al. A 4-Ga Record of Granite Heat Generation: Implications for Early Earth Geodynamic Evolution and Crustal Composition, Precambrian Research (2019). DOI: 10.1016 / j.precamres.2019.105375
M. Gard et al. Variations in Continental Heat Generation from 4 Ga to Present: Hints from Geochemical Data, Lithos (2019). DOI: 10.1016 / j.lithos.2019.05.034
New Model Proposes Lost Continents for Early Earth (2019, July 1)
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