According to a new scientific model, ancient continents may have emerged from the sea much earlier than previously thought, but were eventually destroyed, leaving little traces for us to find today.
According to a new radioactivity model of our planet’s ancient continents, we ought to question the current models for the formation of Earth’s continent crusts.
Scientists argue that ancient continents may have risen from the oceans much earlier than previously thought, although they were destroyed leaving behind little evidence of their existence.
This is according to a group of experts from the University of Adelaide who have presented two new studies on a model of rock radioactivity over billions of years. The new papers argue that our planets continental crust may have been much thicker, and existed earlier than current models predict, with continents existing on our plant dating back as far as 4 billion years.
“We use this model to understand the evolving processes from early Earth to the present, and suggest that the survival of the early crust was dependent on the amount of radioactivity in the rocks – not random chance,” revealed Dr. Derrick Hasterok, from the University of Adelaide’s Department of Earth Sciences and Mawson Centre for Geoscience.
“If our model proves to be correct, it may require revision to many aspects of our understanding of the Earth’s chemical and physical evolution, including the rate of growth of the continents and possibly even the onset of plate tectonics,” Dr. Hasterok added.
After gathering more than 75,800 geochemical samples of igneous rocks, Dr. Hasterock and Ph.D. student Matthew Gard estimated radioactivity in these rocks today and came up with a model of average radioactivity dating back from around 4 billion years all the way to the present era.
“All rocks contain natural radioactivity that produces heat and raises temperatures in the crust when it decays – the more radioactive a rock the more heat it produces, explains Dr. Hasterok.
“Rocks typically associated with the continental crust have higher radioactivity than oceanic rocks. A rock four billion years old would have about four times as much radioactivity when it was created compared with today.”
The study revealed an unexpected discovery; the researchers noted an unexpected deficit in the radioactivity level in rockers that are older than 2 billion years.
After correcting for much greater heat production, due to an estimated higher radioactivity present at the time, the deficits they encountered disappeared.
“We think there would have been more granite-like – or continental-type – rocks around but because of the higher radioactivity, and therefore higher heat, they either melted or were easily destroyed by tectonic movement. That’s why these continental crusts don’t show in the geological record,” the researchers revealed.
“Our prevailing models suggest that continents eventually grew out of the oceans as the crust thickened. But we think there may have been a significant amount of, albeit very unstable, continental crust much earlier.”