The geodynamic setting leading to the formation of Earth’s first continents remains debated. The University of Illinois Chicago‘s David Hernández Uribe used computer models to shed new light on the leading theory of continent formation. They studied the formation of magmas that hold clues to the continents’ origin.
Hernández Uribe looked at magmas with a compositional signature similar to that of zircons dating back to the Archaean period, 2.5 to 4 billion years ago.
Zircons in Archaean granitoid rocks show that the magma originated from a source that was both wet and oxidized. This suggests that subduction (where one tectonic plate moves under another) might have started on Earth between 4.0 and 3.6 billion years ago, during the Eoarchaean era.
Last year, Chinese and Australian scientists argued that Archaean zircons might have originated from subduction. Subduction still happens today, causing earthquakes and volcanic eruptions and reshaping the coasts of continents.
Hernández Uribe, in this study, found that subduction was not necessary to create Archaean zircons. Instead, he discovered that the minerals could form under high pressure and temperature from melting the Earth’s thick primordial crust.
Hernández Uribe said, “Using my calculations and models, you can get the same signatures for zircons and even provide a better match through the partial melting of the bottom of the crust. So based on these results, we still do not have enough evidence to say which process formed the continents.”
The findings also raise uncertainty about when plate tectonics started on Earth. If subduction caused the formation of continents, continents started moving between 3.6 to 4 billion years ago. However, the alternative theory of melting crust forming the first continents means that subduction and tectonics could have started much later.
“Our planet is the only planet in the solar system with active plate tectonics as we know it,” Hernández Uribe said. “And this relates to the origin of life because how the first continents moved controlled the weather, it controlled the chemistry of the oceans, and all that is related to life.”
Journal Reference:
- Hernández-Uribe, D. Generation of Archaean oxidizing and wet magmas from mafic crustal overthickening. Nat. Geosci. (2024). DOI: 10.1038/s41561-024-01489-z