Continents would have emerged much earlier than what was estimated to date in the geological evolution of the Earth, but would have quickly disappeared without a trace, shows a new model of the formation of the continental crust of the planet.
This hypothesis is that of Australian geologists at the University of Adelaide, whose model of the radioactivity of the ancient rocks of the Earth calls into question some of our current theories of continental crust formation.
Landmarks
- Earth was formed 4.6 billion years ago (at the same time as the solar system);
- At first, its surface consisted mainly of partially or completely melted rocks, which then solidified;
- Liquid water would have appeared on its surface barely 100 million years after its formation;
- The continental crust corresponds to the parts of the earth’s crust that form the continents;
- Several supercontinents have formed during the evolution of the Earth: Rodinia, Columbia, Pannotia and Pangea.
Continental dance
The two studies published by geoscientist Derrick Hasterok and his colleagues reveal that the continental crust of the Earth has increased in thickness much earlier than current models indicate, so continents may have formed sooner.
We use this model to understand the evolution of processes from the beginning of the Earth to the present day, and we believe that the survival of a primitive terrestrial crust depended at that time on the amount of radioactivity that it contained, and it was not the result of chance.
Derrick Hasterok, Mawson Geoscience Center, University of Adelaide
“If our model proves to be accurate, we will have to revisit many aspects of our understanding of the chemical and physical evolution of the Earth, particularly with respect to the evolution of continents and perhaps even the beginning of the plate tectonics, “explains the researcher.
To arrive at this hypothesis, the Australian team analyzed not less than 75,800 geochemical samples of igneous rocks (magmatic rocks), whose formation age was estimated on all continents. They calculated the radioactivity in these rocks in order to build a model representing the average radioactivity during the last 4 billion years.
All rocks contain natural radioactivity that produces heat and increases the temperature in the crust as it decays. Thus, the more radioactive a rock is, the more heat it produces.
Derrick Hasterok, Mawson Geoscience Center, University of Adelaide
A geological anomaly
However, researchers have noted that the level of radioactivity of rocks more than 2 billion years old is lower than what they expected.
However, when they adjusted their data to account for a rise in heat caused by higher radioactivity, this difference faded.
Scientists believe that crusts have melted or have been washed away by the tectonic movement. For this reason, not all continental crusts appear in the harvested geological data.
Our models suggest that continents emerged from the oceans as the crust thickened. Continental crusts that, although very unstable, appeared earlier, but soon disappeared thereafter.
Derrick Hasterok, Mawson Geoscience Center, University of Adelaide
Did you know?
In 2017, scientists claimed that New Zealand is at the heart of an eighth continent that could eventually emerge from the ocean.
A model for the future
The authors of this work published in the newspapers Precambrian Research (New Window) and Lithos (New Window ) believe that their new model could have important implications for monitoring the effects of global warming.
What this new model allows us to do is predict the radioactivity of rocks where we have few or no samples, as in Antarctica, where we do not have access to samples.
Martin Hand, Mawson Geoscience Center, University of Adelaide
“It could help us assess ice sheet stability and the threshold of temperature changes necessary for global warming to influence glacial melt,” says Martin Hand.
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