A new study published in the journal Nature by Penn State scientists presents a new theory on how ancient tracts of continental crust called cratons formed some 3 billion years ago, contributing to the stability of Earth’s continents. The researchers suggest that rather than the continents emerging as stable landmasses with granite-enriched upper crusts, exposure of fresh rock to weathering processes triggered geological processes that stabilized the crust. This new understanding may offer insights into how potentially habitable, Earth-like planets evolve.
Cratons, which extend deep into the Earth’s mantle like a keel of a boat, play a crucial role in keeping continents stable over billions of years. This stability is maintained by a combination of weathering processes that concentrated heat-producing elements like uranium, thorium, and potassium in the shallow crust, allowing the deeper crust to cool and harden. This mechanism created a thick, hard layer of rock that protected the bottoms of the continents from deformation, making them characteristic features of cratons.
Collisions between tectonic plates buried sedimentary rocks high in heat-producing elements deep in the Earth’s crust, where they triggered melting of the lower crust. The resulting melts ascended back to the upper crust, trapping these elements in rocks like granite and allowing the lower crust to cool and harden. The process likely occurred between 3 and 2.5 billion years ago, a time when radioactive elements decayed at a faster rate, releasing more heat than today and contributing to the formation of cratons.
The emergence of continents and the formation of cratons possibly played a significant role in Earth’s evolution and the development of habitable environments for life. By creating stable tracts of continental crust close to sea level, these processes may have paved the way for the propagation of life on Earth. The researchers analyzed rock samples from the Archean period to assess radiogenic heat productivity and create thermal models of craton formation, linking rock-based heat production to the emergence of continents.
Cratons, typically found in the interior of continents, contain some of the oldest rocks on Earth but remain challenging to study due to their deep underground origins. While mountain belt formation can bring buried rocks to the surface in tectonically active areas, the core of cratons remains inaccessible. Future research will involve sampling ancient interiors of cratons and drilling core samples to test the model proposed by the researchers. By unlocking the archive of metamorphosed sedimentary rocks that have melted and produced granites, scientists hope to validate their predictions for the flight path of continental crust.
Overall, the study sheds new light on the formation of cratons and the stabilization of Earth’s continents, highlighting the importance of radiogenic heat-producing elements in creating stable tracts of continental crust. The research offers a new perspective on planetary evolution and the role of continents in creating habitable environments for life. Funding for the study was provided by Penn State and the U.S. National Science Foundation.
