A study led by Curtin University in Australia has found new evidence that earth’s first continents were not created by subduction under conditions similar to modern plate tectonics, as previously thought, but by entirely different processes.
In the paper, published in the journal Geology, the team measured isotopes of iron and zinc in rocks taken from central Siberia and South Africa and determined that their composition was likely formed in a non-subduction environment.
The first continents formed early in Earth’s history, more than 3 billion years ago, but how they formed is still up for debate, said lead author Dr Luk-serge Dousay, from curtin University’s School of Earth and Planetary Sciences’ Geodynamics research unit.
“Previous research has shown that the earliest supercontinents formed through subduction and plate tectonics, in which the earth’s plates moved with each other to form mountains and oceans,” Says Dusser.
“The study found that the chemical composition of these rock fragments is not consistent with what we would normally see in a subduction environment,” he said. “If these continents were formed by subduction and plate tectonics, the iron and zinc isotopic ratios would be expected to be very high or very low, but our analysis shows that these isotopic ratios are similar to those found in non-subducted rocks.”
Dusser said his team used a relatively new technique, the unconventional method of stable isotopes, which has been used to determine the formation of continental and mantle rocks.
“Our study provides a new theory of the unknown about how the continents formed on Earth more than three billion years ago,” he said. Further research is needed to determine a specific explanation.”